Electro Voice Computer Monitor 1252 User Manual
Nexus  
1250 /1252  
High Performance SCADA Monitor  
Installation & Operation Manual  
Version 1.25  
November 13, 2006  
Doc # E107706 V1.25  
Electro Industries/GaugeTech  
1800 Shames Drive  
Westbury, New York 11590  
Tel: 516-334-0870 ꢀ Fax: 516-338-4741  
[email protected] ꢀ www.electroind.com  
“The Leader in Web Accessed Power Monitoring and Control”  
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Nexus 1250/1252  
Installation and Operation Manual  
Revision 1.25  
Published by:  
Electro Industries/GaugeTech  
1800 Shames Drive  
Westbury, NY 11590  
All rights reserved. No part of this  
publication may be reproduced or  
transmitted in any form or by any  
means, electronic or mechanical,  
including photocopying, recording,  
or information storage or retrieval  
systems or any future forms of  
duplication, for any purpose other  
than the purchaser’s use, without  
the expressed written permission of  
Electro Industries/GaugeTech.  
© 2006  
Electro Industries/GaugeTech  
Printed in the United States of  
America.  
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Customer Service and Support  
Customer support is available 9:00 am to 4:30 pm, eastern standard time, Monday through Friday.  
Please have the model, serial number and a detailed problem description available. If the problem  
concerns a particular reading, please have all meter readings available. When returning any merchandise  
to EIG, a return materials authorization number is required. For customer or technical assistance, repair  
or calibration, phone 516-334-0870 or fax 516-338-4741.  
Product Warranty  
Electro Industries/GaugeTech warrants all products to be free from defects in material and workmanship  
for a period of four years from the date of shipment. During the warranty period, we will, at our option,  
either repair or replace any product that proves to be defective.  
To exercise this warranty, fax or call our customer-support department. You will receive prompt  
assistance and return instructions. Send the instrument, transportation prepaid, to EIG at 1800 Shames  
Drive, Westbury, NY 11590. Repairs will be made and the instrument will be returned.  
Limitation of Warranty  
This warranty does not apply to defects resulting from unauthorized modification, misuse, or use for any  
reason other than electrical power monitoring. Nexus 1250/1252 is not a user-serviceable product.  
OUR PRODUCTS ARE NOT TO BE USED FOR PRIMARY OVER-CURRENT PROTECTION. ANY  
PROTECTION FEATURE IN OUR PRODUCTS IS TO BE USED FOR ALARM OR SECONDARY  
PROTECTION ONLY.  
THIS WARRANTY IS IN LIEU OF ALL OTHER WARRANTIES, EXPRESSED OR IMPLIED,  
INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY OR FITNESS FOR A  
PARTICULAR PURPOSE. ELECTRO INDUSTRIES/GAUGETECH SHALL NOT BE LIABLE FOR  
ANY INDIRECT, SPECIAL OR CONSEQUENTIAL DAMAGES ARISING FROM ANY AUTHO-  
RIZED OR UNAUTHORIZED USE OF ANY ELECTRO INDUSTRIES/GAUGETECH PRODUCT.  
LIABILITY SHALL BE LIMITED TO THE ORIGINAL COST OF THE PRODUCT SOLD.  
Statement of Calibration  
Our instruments are inspected and tested in accordance with specifications published by Electro  
Industries/GaugeTech. The accuracy and a calibration of our instruments are traceable to the National  
Institute of Standards and Technology through equipment that is calibrated at planned intervals by  
comparison to certified standards.  
Disclaimer  
The information presented in this publication has been carefully checked for reliability; however, no  
responsibility is assumed for inaccuracies. The information contained in this document is subject to  
change without notice.  
This symbol indicates that the operator must refer to an explanation in the operating  
instructions. Please see Chapter 3, Hardware Installation, for important safety  
information regarding installation and hookup of the Nexus 1250/1252 Meter.  
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About Electro Industries/GaugeTech  
Electro Industries/GaugeTech was founded in 1973 by Dr. Samuel Kagan. Dr. Kagan’s first innovation,  
an affordable, easy-to-use AC power meter, revolutionized the power-monitoring field. In the 1980s Dr.  
Kagan and his team at EIG developed a digital multifunction monitor capable of measuring every aspect  
of power.  
EIG further transformed AC power metering and power distribution with the Futura+ device, which  
supplies all the functionality of a fault recorder, an event recorder and a data logger in one single meter.  
Today, with the Nexus 1250/1252,1262/1272 and the Shark, EIG is a leader in the development and  
production of power monitoring products. All EIG products are designed, manufactured, tested and  
calibrated at our facility in Westbury, New York.  
Applications:  
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Multifunction power monitoring  
Single and multifunction power monitoring  
Power quality monitoring  
On board data logging for trending power usage and quality  
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Disturbance analysis  
Futura+ Series Products:  
Q
Power quality monitoring  
High-accuracy AC metering  
On board data logging  
On board fault and voltage recording  
Q
Q
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DM Series Products:  
Q
Three-phase multifunction monitoring  
Wattage, VAR and amperage  
Modbus, Modbus Plus, DNP 3.0 and Ethernet protocols  
Analog retransmit signals (0–1 and 4–20mA)  
Q
Q
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Single-Function Meters:  
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AC voltage and amperage  
DC voltage and amperage  
AC wattage  
Single-phase monitoring with maximum and minimum demands  
Transducer readouts  
Q
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Portable Analyzers:  
Q
Power quality analysis  
Energy analysis  
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Table of Contents  
Chapter 1: Three-Phase Power Measurement  
1.1: Three-Phase System Configurations . . . . . . . . . . . . . . . . . . . . . 1-1  
1.1.1: Wye Connnection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1  
1.1.2: Delta Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3  
1.1.3: Blondell’s Theorem and Three Phase Measurement . . . . . . . . . . . . . 1-4  
1.2: Power, Energy and Demand . . . . . . . . . . . . . . . . . . . . . . . . 1-6  
1.3: Reactive Energy and Power Factor . . . . . . . . . . . . . . . . . . . . . 1-8  
1.4: Harmonic Distortion . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-10  
1.5: Power Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-13  
Chapter 2: Nexus Overview  
2.1: The Nexus System . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1  
2.2: DNP V3.00 Level 1 and Level 2 . . . . . . . . . . . . . . . . . . . . . . 2-2  
2.3: Flicker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2  
2.4: INP2 Internal Modem with Dial-In/Dial-Out Option . . . . . . . . . . . . . . 2-3  
2.4.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3  
2.4.2: Dial-In Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3  
2.4.3: Dial-Out Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3  
2.5: Total Web Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4  
2.5.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4  
2.5.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4  
2.6: Measurements and Calculations . . . . . . . . . . . . . . . . . . . . . . . 2-6  
2.7: Demand Integrators . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10  
2.8: Nexus External I/O Modules (Optional) . . . . . . . . . . . . . . . . . . . 2-12  
2.9: Nexus 1250/1252 Meter Specifications . . . . . . . . . . . . . . . . . . . 2-13  
2.10: Nexus P40N, P41N, P43N External Display Specifications . . . . . . . . . . 2-14  
2.11: Nexus P60N Touch Screen Display Specifications . . . . . . . . . . . . . . 2-14  
Chapter 3: Hardware Installation  
3.1: Mounting the Nexus 1259/1252 Meter . . . . . . . . . . . . . . . . . . . . 3-1  
3.2: Mounting the Nexus P40N, P41N, P43N External Displays . . . . . . . . . . . 3-3  
3.3: Mounting the Nexus P60N Touch Screen External Display . . . . . . . . . . . 3-4  
3.4: Mounting the Nexus External I/O Modules . . . . . . . . . . . . . . . . . . 3-6  
Chapter 4: Electrical Installation  
4.1: Wiring the Monitored Inputs and Voltages . . . . . . . . . . . . . . . . . . 4-1  
4.2: Fusing the Voltage Connections . . . . . . . . . . . . . . . . . . . . . . . 4-1  
4.3: Wiring the Monitored Inputs -VRef . . . . . . . . . . . . . . . . . . . . . 4-1  
4.4: Wiring the Monitored Inputs - VAux . . . . . . . . . . . . . . . . . . . . . 4-1  
4.5: Wiring the Monitored Inputs - Currents . . . . . . . . . . . . . . . . . . . 4-1  
4.6: Isolating a CT Connection Reversal . . . . . . . . . . . . . . . . . . . . . 4-2  
4.7: Instrument Power Connections . . . . . . . . . . . . . . . . . . . . . . . 4-2  
4.8: Wiring Diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3  
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Chapter 5: Communication Wiring  
5.1: Communication Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5-1  
5.2: RS-232 Connection-Nexus Meter to a Computer . . . . . . . . . . . . . . . 5-5  
5.3: RS-485 Wiring Fundamentals (with RT Explanation) . . . . . . . . . . . . . . 5-5  
5.4: RS-485 Connection- Nexus Meter to a Computer or PLC . . . . . . . . . . . . 5-8  
5.5: RJ-11 (Telephone Line) Connection- Nexus with Internal Modem Option to PC . . 5-8  
5.6: RJ-45 Connection- Nexus with Internal Network Option to multiple PC’s . . . . . 5-8  
5.7: RS-485 Connection- Nexus to an RS-485 Master (Unicom or Modem Manager) . . 5-9  
5.7.1: Using the Unicom 2500 . . . . . . . . . . . . . . . . . . . . . . . . . 5-9  
5.8: RS-485 Connectiion- Nexus Meter to P40N, P41N, P43N External Display . . . 5-11  
5.9: RS-485 Connectiion- Nexus Meter to P60N External Display . . . . . . . . . 5-12  
5.10: Communication Ports on the Nexus I/O Modules . . . . . . . . . . . . . . 5-13  
5.11: RS-485 Connection—Nexus Meter to Nexus I/O Modules . . . . . . . . . . 5-14  
5.12: Steps to Determine Power Needed . . . . . . . . . . . . . . . . . . . . . 5-15  
5.13: I/O Modules’ Factory Settings and VA Ratings . . . . . . . . . . . . . . . 5-15  
5.14: Linking Multiple Nexus Devices in Series . . . . . . . . . . . . . . . . . 5-16  
5.15: Networking Groups of Nexus Meters . . . . . . . . . . . . . . . . . . . 5-17  
5.16: Remote Communication Overview . . . . . . . . . . . . . . . . . . . . 5-18  
5.17: Remote Communication- RS-232 . . . . . . . . . . . . . . . . . . . . . 5-21  
5.18: Remote Communication- RS-485 . . . . . . . . . . . . . . . . . . . . . 5-21  
5.19: Programming Modems for Remote Communication . . . . . . . . . . . . . 5-22  
5.20: Selected Modem Strings . . . . . . . . . . . . . . . . . . . . . . . . . 5-23  
5.21: High Speed Inputs Connection . . . . . . . . . . . . . . . . . . . . . . 5-23  
5.22: Five Modes of Time Synchronization . . . . . . . . . . . . . . . . . . . 5-24  
5.23: IRIG-B Connections . . . . . . . . . . . . . . . . . . . . . . . . . . 5-25  
Chapter 6: Using the Nexus External Displays  
6.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1  
6.2: Nexus P40N, P41N, P43N LED External Display . . . . . . . . . . . . . . . 6-1  
6.2.1: Connect Multiple Displays . . . . . . . . . . . . . . . . . . . . . . . . 6-2  
6.2.2: Nexus P40N Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2  
6.3: Dynamic Readings Mode . . . . . . . . . . . . . . . . . . . . . . . . . 6-3  
6.4: Navigational Map of Dynamic Readings Mode . . . . . . . . . . . . . . . . 6-5  
6.5: Nexus Information Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6  
6.6: Navigational Map of Nexus Information Mode . . . . . . . . . . . . . . . . 6-7  
6.7: Display Features Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8  
6.8: Navigational Map of Display Features Mode . . . . . . . . . . . . . . . . . 6-9  
6.9: Nexus P60N Touch Screen External Display . . . . . . . . . . . . . . . . . 6-10  
6.10: Navigational Map for P60N Touch Screen External Display . . . . . . . . . 6-18  
Chapter 7: Transformer Loss Compensation  
7.1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1  
7.2: Nexus 1250/1252 Transformer Loss Compensation . . . . . . . . . . . . . . 7-3  
7.2.1: Loss Compensation in Three Element Installations . . . . . . . . . . . . . . 7-4  
7.2.1.1: Three Element Loss Compensation Worksheet . . . . . . . . . . . . . . . 7-5  
Chapter 8: Nexus Time-of-Use  
8.1: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1  
8.2: The Nexus TOU Calendar . . . . . . . . . . . . . . . . . . . . . . . . . 8-1  
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8.3: TOU Prior Season and Month . . . . . . . . . . . . . . . . . . . . . . . 8-2  
8.4: Updating, Retrieving and Replacing TOU Calendars . . . . . . . . . . . . . . 8-2  
8.5: Daylight Savings and Demand . . . . . . . . . . . . . . . . . . . . . . . 8-2  
Chapter 9: Nexus External I/O Modules  
9.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1  
9.1.1: Port Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-2  
9.2: Installing Nexus External I/O Modules . . . . . . . . . . . . . . . . . . . 9-3  
9.2.1: Power Source for I/O Modules . . . . . . . . . . . . . . . . . . . . . . 9-4  
9.3: Using PSIO with Multiple I/O Modules . . . . . . . . . . . . . . . . . . . 9-5  
9.3.1: Steps for Attaching Multiple I/O Modules . . . . . . . . . . . . . . . . . 9-5  
9.4: Factory Settings and Reset Button . . . . . . . . . . . . . . . . . . . . . 9-6  
9.5: Analog Transducer Signal Output Modules . . . . . . . . . . . . . . . . . . 9-7  
9.5.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-7  
9.5.2: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-8  
9.6: Analog Input Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9  
9.6.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-9  
9.6.2: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-10  
9.7: Digital Dry Contact Relay Output (Form C) Module . . . . . . . . . . . . . 9-11  
9.7.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-11  
9.7.2: Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12  
9.7.3: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-12  
9.8: Digital Solid State Pulse Output (KYZ) Module . . . . . . . . . . . . . . . 9-13  
9.8.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-13  
9.8.2: Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14  
9.8.3: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-14  
9.9: Digital Status Input Module . . . . . . . . . . . . . . . . . . . . . . . . 9-15  
9.9.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15  
9.9.2: Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-15  
9.9.3: Normal Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16  
9.10: Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-16  
Chapter 10: Nexus Monitor with INP2 - Internal Modem Option  
10.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1  
10.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2  
10.3: Dial-In Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2  
10.4: Dial-Out Function . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-2  
Chapter 11: Nexus Monitor with Internal Network Option  
11.1: Hardware Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1  
11.2: Hardware Connection . . . . . . . . . . . . . . . . . . . . . . . . . . 11-3  
Chapter 12: Flicker  
12.1: Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1  
12.2: Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 12-1  
12.3: Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-3  
12.4: Software - User Interface . . . . . . . . . . . . . . . . . . . . . . . . 12-4  
12.5: Logging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7  
12.6: Polling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7  
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12.7: Log Viewer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-7  
12.8: Performance Notes . . . . . . . . . . . . . . . . . . . . . . . . . . . 12-8  
Appendix A: Transformer Loss Compensation Excel Spreadsheet with Examples  
A.1: Calculating Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1  
A.2: Excel Spreadsheet with Example Numbers . . . . . . . . . . . . . . . . . A-1  
Glossary of Terms  
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Chapter 1  
Three-Phase Power Measurement  
This introduction to three-phase power and power measurement is intended to provide only a brief  
overview of the subject. The professional meter engineer or meter technician should refer to more  
advanced documents such as the EEI Handbook for Electricity Metering and the application standards  
for more in-depth and technical coverage of the subject.  
1.1: Three-Phase System Configurations  
Three-phase power is most commonly used in situations where large amounts of power will be used  
because it is a more effective way to transmit the power and because it provides a smoother delivery  
of power to the end load. There are two commonly used connections for three-phase power, a wye  
connection or a delta connection. Each connection has several different manifestations in actual use.  
When attempting to determine the type of connection in use, it is a good practice to follow the  
circuit back to the transformer that is serving the circuit. It is often not possible to conclusively  
determine the correct circuit connection simply by counting the wires in the service or checking  
voltages. Checking the transformer connection will provide conclusive evidence of the circuit  
connection and the relationships between the phase voltages and ground.  
1.1.1: Wye Connection  
Q
The wye connection is so called because when you look at the phase relationships and the winding  
relationships between the phases it looks like a wye (Y). Figure 1.1 depicts the winding relationships  
for a wye-connected service. In a wye service the neutral (or center point of the wye) is typically  
grounded. This leads to common voltages of 208/120 and 480/277 (where the first number represents  
the phase-to-phase voltage and the second number represents the phase-to-ground voltage).  
Phase B  
Phase C  
Phase A  
Figure 1.1: Three-Phase Wye Winding  
o
Q
The three voltages are separated by 120 electrically. Under balanced load conditions with unity  
o
power factor the currents are also separated by 120 . However, unbalanced loads and other  
o
conditions can cause the currents to depart from the ideal 120 separation.  
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Three-phase voltages and currents are usually represented with a phasor diagram. A phasor diagram  
for the typical connected voltages and currents is shown in Figure 1.2.  
Fig 1.2: Phasor Diagram Showing Three-phase Voltages and Currents  
o
Q
The phasor diagram shows the 120 angular separation between the phase voltages. The phase-to-  
phase voltage in a balanced three-phase wye system is 1.732 times the phase-to-neutral voltage. The  
center point of the wye is tied together and is typically grounded. Table 1.1 shows the common  
voltages used in the United States for wye-connected systems.  
Phase-to-Ground Voltage  
120 volts  
Phase-to-Phase Voltage  
208 volts  
277 volts  
480 volts  
2,400 volts  
4,160 volts  
7,200 volts  
12,470 volts  
13,200 volts  
7,620 volts  
Table 1.1: Common Phase Voltages on Wye Services  
Q
Usually a wye-connected service will have four wires; three wires for the phases and one for the  
neutral. The three-phase wires connect to the three phases (as shown in Figure 1.1). The neutral wire  
is typically tied to the ground or center point of the wye (refer to Figure 1.1).  
In many industrial applications the facility will be fed with a four-wire wye service but only three  
wires will be run to individual loads. The load is then often referred to as a delta-connected load but  
the service to the facility is still a wye service; it contains four wires if you trace the circuit back  
to its source (usually a transformer). In this type of connection the phase to ground voltage will be  
the phase-to-ground voltage indicated in Table 1, even though a neutral or ground wire is not  
physically present at the load. The transformer is the best place to determine the circuit connection  
type because this is a location where the voltage reference to ground can be conclusively identified.  
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1.1.2: Delta Connection  
Q
Delta connected services may be fed with either three wires or four wires. In a three-phase delta  
service the load windings are connected from phase-to-phase rather than from phase-to-ground.  
Figure 1.3 shows the physical load connections for a delta service.  
Phase C  
Phase A  
Phase B  
Figure 1.3: Three-Phase Delta Winding Relationship  
In this example of a delta service, three wires will transmit the power to the load. In a true delta  
service, the phase-to-ground voltage will usually not be balanced because the ground is not at the  
center of the delta.  
Figure 1.4 shows the phasor relationships between voltage and current on a three-phase delta circuit.  
In many delta services, one corner of the delta is grounded. This means the phase to ground voltage  
will be zero for one phase and will be full phase-to-phase voltage for the other two phases. This is  
done for protective purposes.  
Vca  
Ic  
Vbc  
Ia  
Ib  
Vab  
Figure 1.4: Phasor Diagram, Three-Phase Voltages and Currents Delta Connected.  
Q
Another common delta connection is the four-wire, grounded delta used for lighting loads. In this  
connection the center point of one winding is grounded. On a 120/240 volt, four-wire, grounded  
delta service the phase-to-ground voltage would be 120 volts on two phases and 208 volts on the  
third phase. Figure 1.5 shows the phasor diagram for the voltages in a three-phase, four-wire delta  
system.  
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Fig 1.5: Phasor Diagram Showing Three-phase, Four-wire Delta Connected System  
1.1.3: Blondell’s Theorem and Three Phase Measurement  
In 1893 an engineer and mathematician named Andre E. Blondell set forth the first scientific basis  
for poly phase metering. His theorem states:  
Q
If energy is supplied to any system of conductors through N wires, the total power in the system is  
given by the algebraic sum of the readings of N wattmeters so arranged that each of the N wires  
contains one current coil, the corresponding potential coil being connected between that wire and  
some common point. If this common point is on one of the N wires, the measurement may be made  
by the use of N-1 wattmeters.  
The theorem may be stated more simply, in modern language:  
Q
In a system of N conductors, N-1 meter elements will measure the power or energy taken provided  
that all the potential coils have a common tie to the conductor in which there is no current coil.  
Q
Three-phase power measurement is accomplished by measuring the three individual phases and  
adding them together to obtain the total three phase value. In older analog meters, this  
measurement was accomplished using up to three separate elements. Each element combined the  
single-phase voltage and current to produce a torque on the meter disk. All three elements were  
arranged around the disk so that the disk was subjected to the combined torque of the three elements.  
As a result the disk would turn at a higher speed and register power supplied by each of the three  
wires.  
Q
According to Blondell's Theorem, it was possible to reduce the number of elements under certain  
conditions. For example, a three-phase, three-wire delta system could be correctly measured with  
two elements (two potential coils and two current coils) if the potential coils were connected  
between the three phases with one phase in common.  
In a three-phase, four-wire wye system it is necessary to use three elements. Three voltage coils are  
connected between the three phases and the common neutral conductor. A current coil is required in  
each of the three phases.  
Q
In modern digital meters, Blondell's Theorem is still applied to obtain proper metering. The  
difference in modern meters is that the digital meter measures each phase voltage and current and  
calculates the single-phase power for each phase. The meter then sums the three phase powers to a  
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single three-phase reading.  
Some digital meters calculate the individual phase power values one phase at a time. This means the  
meter samples the voltage and current on one phase and calculates a power value. Then it samples the  
second phase and calculates the power for the second phase. Finally, it samples the third phase and  
calculates that phase power. After sampling all three phases, the meter combines the three readings to  
create the equivalent three-phase power value. Using mathematical averaging techniques, this method  
can derive a quite accurate measurement of three-phase power.  
More advanced meters actually sample all three phases of voltage and current simultaneously and  
calculate the individual phase and three-phase power values. The advantage of simultaneous sampling  
is the reduction of error introduced due to the difference in time when the samples were taken.  
C
Phase B  
Phase C  
B
Node “n”  
A
Phase A  
N
Figure 1.6:  
Three-Phase Wye Load illustrating Kirchhoff’s Law  
and Blondell’s Theorem  
Blondell's Theorem is a derivation that results from Kirchhoff's Law. Kirchhoff's Law states that the  
sum of the currents into a node is zero. Another way of stating the same thing is that the current into a  
node (connection point) must equal the current out of the node. The law can be applied to measuring  
three-phase loads. Figure 1.6 shows a typical connection of a three-phase load applied to a three-  
phase, four-wire service. Krichhoff's Laws hold that the sum of currents A, B, C and N must equal zero  
or that the sum of currents into Node "n" must equal zero.  
If we measure the currents in wires A, B and C, we then know the current in wire N by Kirchhoff's  
Law and it is not necessary to measure it. This fact leads us to the conclusion of Blondell's Theorem  
that we only need to measure the power in three of the four wires if they are connected by a common  
node. In the circuit of Figure 1.6 we must measure the power flow in three wires. This will require  
three voltage coils and three current coils (a three element meter). Similar figures and conclusions  
could be reached for other circuit configurations involving delta-connected loads.  
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1.2: Power, Energy and Demand  
Q
It is quite common to exchange power, energy and demand without differentiating between the  
three. Because this practice can lead to confusion, the differences between these three  
measurements will be discussed.  
Q
Power is an instantaneous reading. The power reading provided by a meter is the present flow of  
watts. Power is measured immediately just like current. In many digital meters, the power value is  
actually measured and calculated over a one second interval because it takes some amount of time to  
calculate the RMS values of voltage and current. But this time interval is kept small to preserve the  
instantaneous nature of power.  
Q
Energy is always based on some time increment; it is the integration of power over a defined time  
increment. Energy is an important value because almost all electric bills are based, in part, on the  
amount of energy used.  
Q
Typically, electrical energy is measured in units of kilowatt-hours (kWh). A kilowatt-hour  
represents a constant load of one thousand watts (one kilowatt) for one hour. Stated another way, if  
the power delivered (instantaneous watts) is measured as 1,000 watts and the load was served for a  
one hour time interval then the load would have absorbed one kilowatt-hour of energy. A different  
load may have a constant power requirement of 4,000 watts. If the load were served for one hour it  
would absorb four kWh. If the load were served for 15 minutes it would absorb ¼ of that total or  
one kWh.  
Q
Figure 1.7 shows a graph of power and the resulting energy that would be transmitted as a result of  
the illustrated power values. For this illustration, it is assumed that the power level is held constant  
for each minute when a measurement is taken. Each bar in the graph will represent the power load  
for the one-minute increment of time. In real life the power value moves almost constantly.  
Q
The data from Figure 1.7 is reproduced in Table 2 to illustrate the calculation of energy. Since the  
time increment of the measurement is one minute and since we specified that the load is constant  
over that minute, we can convert the power reading to an equivalent consumed energy reading by  
multiplying the power reading times 1/60 (converting the time base from minutes to hours).  
Kilowatts  
100  
80  
60  
40  
20  
Time (minutes) Æ  
Figure 1.7: Power Use Over Time  
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Time Interval  
(Minute)  
Accumulated  
Energy (kWh)  
Power (kW)  
Energy (kWh)  
1
2
30  
50  
40  
55  
60  
60  
70  
70  
60  
70  
80  
50  
50  
70  
80  
0.50  
0.83  
0.67  
0.92  
1.00  
1.00  
1.17  
1.17  
1.00  
1.17  
1.33  
0.83  
0.83  
1.17  
1.33  
0.50  
1.33  
3
2.00  
4
2.92  
5
3.92  
6
4.92  
7
6.09  
8
7.26  
9
8.26  
10  
11  
12  
13  
14  
15  
9.43  
10.76  
12.42  
12.42  
13.59  
14.92  
Table 1.2: Power and Energy Relationship Over Time  
As in Table 1.2, the accumulated energy for the power load profile of Figure 1.7 is 14.92 kWh.  
Q
Demand is also a time-based value. The demand is the average rate of energy use over time. The  
actual label for demand is kilowatt-hours/hour but this is normally reduced to kilowatts. This makes  
it easy to confuse demand with power. But demand is not an instantaneous value. To calculate  
demand it is necessary to accumulate the energy readings (as illustrated in Figure 1.7) and adjust the  
energy reading to an hourly value that constitutes the demand.  
In the example, the accumulated energy is 14.92 kWh. But this measurement was made over a  
15-minute interval. To convert the reading to a demand value, it must be normalized to a 60-minute  
interval. If the pattern were repeated for an additional three 15-minute intervals the total energy  
would be four times the measured value or 59.68 kWh. The same process is applied to calculate the  
15-minute demand value. The demand value associated with the example load is 59.68 kWh/hr or  
59.68 kWd. Note that the peak instantaneous value of power is 80 kW, significantly more than the  
demand value.  
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Q
Figure 1.8 shows another example of energy and demand. In this case, each bar represents the  
energy consumed in a 15-minute interval. The energy use in each interval typically falls between 50  
and 70 kWh. However, during two intervals the energy rises sharply and peaks at 100 kWh in  
interval number 7. This peak of usage will result in setting a high demand reading. For each interval  
shown the demand value would be four times the indicated energy reading. So interval 1 would have  
an associated demand of 240 kWh/hr. Interval 7 will have a demand value of 400 kWh/hr. In the  
data shown, this is the peak demand value and would be the number that would set the demand  
charge on the utility bill.  
Kilowatt-hours  
100  
80  
60  
40  
20  
Intervals Æ  
Figure 1.8: Energy Use and Demand  
Q
As can be seen from this example, it is important to recognize the relationships between power,  
energy and demand in order to control loads effectively or to monitor use correctly.  
1.3: Reactive Energy and Power Factor  
Q
The real power and energy measurements discussed in the previous section relate to the quantities  
that are most used in electrical systems. But it is often not sufficient to only measure real power and  
energy. Reactive power is a critical component of the total power picture because almost all real-life  
applications have an impact on reactive power. Reactive power and power factor concepts relate to  
both load and generation applications. However, this discussion will be limited to analysis of  
reactive power and power factor as they relate to loads. To simplify the discussion, generation will  
not be considered.  
Q
Real power (and energy) is the component of power that is the combination of the voltage and the  
value of corresponding current that is directly in phase with the voltage. However, in actual practice  
the total current is almost never in phase with the voltage. Since the current is not in phase with the  
voltage, it is necessary to consider both the inphase component and the component that is at  
o
quadrature (angularly rotated 90 or perpendicular) to the voltage. Figure 1.9 shows a single-phase  
voltage and current and breaks the current into its in-phase and quadrature components.  
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IR  
V
Angle θ  
IX  
I
Figure 1.9: Voltage and Complex  
Q
The voltage (V) and the total current (I) can be combined to calculate the apparent power or VA.  
The voltage and the in-phase current (IR) are combined to produce the real power or watts. The volt-  
age and the quadrature current (IX) are combined to calculate the reactive power.  
The quadrature current may be lagging the voltage (as shown in Figure 1.9) or it may lead the  
voltage. When the quadrature current lags the voltage the load is requiring both real power (watts)  
and reactive power (VARs). When the quadrature current leads the voltage the load is requiring real  
power (watts) but is delivering reactive power (VARs) back into the system; that is VARs are  
flowing in the opposite direction of the real power flow.  
Q
Reactive power (VARs) is required in all power systems. Any equipment that uses magnetization to  
operate requires VARs. Usually the magnitude of VARs is relatively low compared to the real power  
quantities. Utilities have an interest in maintaining VAR requirements at the customer to a low value  
in order to maximize the return on plant invested to deliver energy. When lines are carrying VARs,  
they cannot carry as many watts. So keeping the VAR content low allows a line to carry its full  
capacity of watts. In order to encourage customers to keep VAR requirements low, most utilities  
impose a penalty if the VAR content of the load rises above a specified value.  
A common method of measuring reactive power requirements is power factor. Power factor can be  
defined in two different ways. The more common method of calculating power factor is the ratio of  
the real power to the apparent power. This relationship is expressed in the following formula:  
Total PF = real power / apparent power = watts/VA  
This formula calculates a power factor quantity known as Total Power Factor. It is called Total PF  
because it is based on the ratios of the power delivered. The delivered power quantities will include  
the impacts of any existing harmonic content. If the voltage or current includes high levels of  
harmonic distortion the power values will be affected. By calculating power factor from the power  
values, the power factor will include the impact of harmonic distortion. In many cases this is the  
preferred method of calculation because the entire impact of the actual voltage and current are  
included.  
A second type of power factor is Displacement Power Factor. Displacement PF is based on the  
angular relationship between the voltage and current. Displacement power factor does not consider  
the magnitudes of voltage, current or power. It is solely based on the phase angle differences. As a  
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result, it does not include the impact of harmonic distortion. Displacement power factor is calculated  
using the following equation:  
Displacement PF = cos θ, where θ is the angle between the voltage and the current (see Fig. 1.9).  
In applications where the voltage and current are not distorted, the Total Power Factor will equal the  
Displacement Power Factor. But if harmonic distortion is present, the two power factors will not be  
equal.  
1.4: Harmonic Distortion  
Q
Harmonic distortion is primarily the result of high concentrations of non-linear loads. Devices such  
as computer power supplies, variable speed drives and fluorescent light ballasts make current  
demands that do not match the sinusoidal waveform of AC electricity. As a result, the current  
waveform feeding these loads is periodic but not sinusoidal. Figure 1.10 shows a normal, sinusoidal  
current waveform. This example has no distortion.  
A Phase Current  
1500  
1000  
500  
0
1
33  
65  
-500  
-1000  
-1500  
Figure 1.10: Nondistorted Current Waveform  
Q
Figure 1.11 shows a current waveform with a slight amount of harmonic distortion. The waveform is  
still periodic and is fluctuating at the normal 60 Hz frequency. However, the waveform is not a  
smooth sinusoidal form as seen in Figure 1.10.  
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Total A Phase Current with Harmonics  
1500  
1000  
500  
0
1
33  
65  
-500  
-1000  
-1500  
Figure 1.11: Distorted Current Wave  
Q
The distortion observed in Figure 1.11 can be modeled as the sum of several sinusoidal waveforms  
of frequencies that are multiples of the fundamental 60 Hz frequency. This modeling is performed  
by mathematically disassembling the distorted waveform into a collection of higher frequency  
waveforms. These higher frequency waveforms are referred to as harmonics. Figure 1.12 shows the  
content of the harmonic frequencies that make up the distortion portion of the waveform in Figure  
1.11.  
Expanded Harmonic Currents  
250  
200  
150  
100  
50  
0
-50  
-100  
-150  
-200  
-250  
2 Harmonic Current  
7 Harmonic Current  
3 Harmonic Current  
ACurrent Total Hrm  
5 Harmonic Current  
Figure 1.12: Waveforms of the Harmonics  
The waveforms shown in Figure 1.12 are not smoothed but do provide an indication of the impact of  
combining multiple harmonic frequencies together.  
When harmonics are present it is important to remember that these quantities are operating at higher  
frequencies. Therefore, they do not always respond in the same manner as 60 Hz values.  
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Q
Inductive and capacitive impedance are present in all power systems. We are accustomed to thinking  
about these impedances as they perform at 60 Hz. However, these impedances are subject to  
frequency variation.  
XL = jωL and  
XC = 1/jωC  
th  
At 60 Hz, ω = 377; but at 300 Hz (5 harmonic) ω = 1,885. As frequency changes impedance  
changes and system impedance characteristics that are normal at 60 Hz may behave entirely  
different in presence of higher order harmonic waveforms.  
Traditionally, the most common harmonics have been the low order, odd frequencies, such as the  
rd th th  
th  
3 , 5 , 7 , and 9 . However newer, new-linear loads are introducing significant quantities of  
higher order harmonics.  
Q
Since much voltage monitoring and almost all current monitoring is performed using instrument  
transformers, the higher order harmonics are often not visible. Instrument transformers are designed  
to pass 60 Hz quantities with high accuracy. These devices, when designed for accuracy at low  
frequency, do not pass high frequencies with high accuracy; at frequencies above about 1200 Hz  
they pass almost no information. So when instrument transformers are used, they effectively filter  
out higher frequency harmonic distortion making it impossible to see.  
Q
However, when monitors can be connected directly to the measured circuit (such as direct  
connection to 480 volt bus) the user may often see higher order harmonic distortion. An important  
rule in any harmonics study is to evaluate the type of equipment and connections before drawing a  
conclusion. Not being able to see harmonic distortion is not the same as not having harmonic  
distortion.  
Q
It is common in advanced meters to perform a function commonly referred to as waveform capture.  
Waveform capture is the ability of a meter to capture a present picture of the voltage or current  
waveform for viewing and harmonic analysis. Typically a waveform capture will be one or two  
cycles in duration and can be viewed as the actual waveform, as a spectral view of the harmonic  
content, or a tabular view showing the magnitude and phase shift of each harmonic value. Data  
collected with waveform capture is typically not saved to memory. Waveform capture is a real-time  
data collection event.  
Waveform capture should not be confused with waveform recording that is used to record multiple  
cycles of all voltage and current waveforms in response to a transient condition.  
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1.5: Power Quality  
Q
Power quality can mean several different things. The terms "power quality" and "power quality  
problem" have been applied to all types of conditions. A simple definition of "power quality  
problem" is any voltage, current or frequency deviation that results in mis-operation or failure of  
customer equipment or systems. The causes of power quality problems vary widely and may  
originate in the customer equipment, in an adjacent customer facility or with the utility.  
In his book Power Quality Primer, Barry Kennedy provided information on different types of power  
quality problems. Some of that information is summarized in Table 1.3 below.  
Cause  
Disturbance Type  
Source  
Lightning  
Transient voltage disturbance,  
sub-cycle duration  
Electrostatic discharge  
Load switching  
Impulse Transient  
Capacitor switching  
Line/cable switching  
Capacitor switching  
Load switching  
Oscillatory transient  
with decay  
Transient voltage, sub-cycle  
duration  
RMS voltage, multiple cycle  
duration  
Sag / swell  
Remote system faults  
System protection  
RMS voltage, multiple second or Circuit breakers  
Interruptions  
longer duration  
Fuses  
Maintenance  
RMS voltage, steady state,  
multiple second or longer  
duration  
Motor starting  
Load variations  
Load dropping  
Undervoltage /  
Overvoltage  
Intermittent loads  
Motor starting  
Arc furnaces  
RMS voltage, steady state,  
repetitive condition  
Voltage flicker  
Steady state current or voltage, Non-linear loads  
long term duration System resonance  
Harmonic distortion  
Table 1.3: Typical Power Quality Problems and Sources  
Q
It is often assumed that power quality problems originate with the utility. While it is true that may  
power quality problems can originate with the utility system, many problems originate with  
customer equipment. Customer-caused problems may manifest themselves inside the customer  
location or they may be transported by the utility system to another adjacent customer. Often,  
equipment that is sensitive to power quality problems may in fact also be the cause of the problem.  
Q
If a power quality problem is suspected, it is generally wise to consult a power quality professional  
for assistance in defining the cause and possible solutions to the problem.  
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Chapter 2  
Nexus Overview  
2.1: The Nexus System  
Electro Industries’ Nexus 1250/1252 combines high-end revenue metering with sophisticated power  
quality analysis. Its advanced monitoring capabilities provide detailed and precise pictures of any  
metered point within a distribution network. The P60N, P40N, P41N and P43N displays are detailed in  
Chapter 6. Extensive I/O capability is available in conjunction with all metering functions. The optional  
Communicator EXT software allows a user to poll and gather data from multiple Nexus meters installed  
at local or remote locations (see the Communicator EXT User Manual for details). On board mass  
memory enables the Nexus to retrieve and store multiple logs. The Nexus Meter with Internal Modem  
(or Network) Option connects to a PC via standard phone line (or MODBUS/TCP) and a daisy chain of  
Nexus Meters via an RS-485 connection. See Chapters 10 and 11 for details.  
Modem/Ethernet  
Option  
Modem Gateway or  
Ethernet Gateway  
RS-485 Connection  
Computer  
or SCADA  
System  
Expandable I/O Modules  
Nexus  
Display  
Modem/Ethernet  
Option  
RJ-11 or RJ-45  
Connection  
Nexus Meter  
Figure 2.1: The Nexus 1250/1252 System  
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Q
Nexus 1250/1252 Revenue Metering:  
•
•
•
•
•
•
Delivers laboratory-grade 0.04% Watt-hour accuracy in a field-mounted device.  
Autocalibrates when there is a temperature change of more than 10 degrees centigrade.  
Exceeds all ANSI C-12 and IEC 687 specifications.  
Adjusts for transformer and line losses, using user-defined compensation factors.  
Automatically logs time-of-use for up to eight programmable tariff registers.  
Counts pulses and aggregates different loads.  
Q
Nexus 1250/1252 Power Quality Monitoring:  
•
•
•
•
•
Records up to 512 samples per cycle on an event.  
Records sub-cycle transients on voltage or current readings.  
Measures and records Harmonics to the 83rd order.  
Offers inputs for neutral-to-ground voltage measurements.  
Synchronizes with IRIG-B clock signal.  
Q
Nexus 1250/1252 Memory, Communication and Control:  
•
•
•
•
•
•
Up to 4 Meg NVRAM.  
4 High Speed Communication Ports.  
Multiple Protocols (see section below on DNP V3.00).  
Built-in RTU functionality.  
Built-in PLC functionality.  
90msec High Speed Updates for Control.  
2.2: DNP V3.00 Level 1 and Level 2  
Nexus 1250 supports DNP V3.00 Level 1.  
Nexus 1252 supports DNP V3.00 Level 2.  
DNP Level 2 Features:  
•
Up to 136 measurement (64 Binary Inputs, 8 Binary Counters, 64 Analog Inputs) can be mapped  
to DNP Static Points (over 3000) in the customizable DNP Point Map.  
Up to 16 Relays and 8 Resets can be controlled through DNP Level 2.  
Report-by-Exception Processing (DNP Events) Deadbands can be set on a per-point basis.  
Freeze Commands: Freeze, Freeze/No-Ack, Freeze with Time, Freeze with Time/No-Ack.  
Freeze with Time Commands enable the Nexus meter to have internal time-driven Frozen and  
Frozen Event data. When the Nexus meter receives the Time and Interval, the data will be  
created.  
•
•
•
•
For complete details, download the appropriate DNP User Manual from our website  
www.electroind.com.  
2.3: Flicker  
Nexus 1252 provides Flicker Evaluation in Instantaneous, Short Term and Long Term Forms.  
For a detailed explanation of Flicker, see Chapter 12 of this manual.  
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2.4: INP2 Internal Modem with Dial-In/Dial-Out Option  
2.4.1: Hardware Overview  
Q
The INP2 Option for the Nexus 1250/1252 meter provides a direct connection to a standard tele-  
phone line. No additional hardware is required to establish a communication connection between the  
meter and a remote computer. The RJ-11 Jack is on the face of the meter. A standard telephone RJ-  
11 plug can connect the meter to a standard PSTN (Public Switched Telephone Network).  
Q
The modem operates at up to 56k baud. The modem supports both incoming calls (from a remote  
computer) and automatic dial-out calls when a defined event must be automatically reported.  
With the device configured with the INP2 Option, the meter has dial-in capability and provides  
remote access to other Modbus-based serial devices via the meter’s RS-485 Gateway over your  
phone line. The meter will recognize and respond to a Modbus Address of 1. With any other  
address, the command will pass through the gateway and become a virtual connection between the  
Remote Modbus Master and any Modbus Slave connected to the RS-485 Gateway.  
2.4.2: Dial-In Function  
Q
The modem continuously monitors the telephone line to detect an incoming call. When an incoming  
call is detected, the modem will wait a user-set number of rings and answer the call.  
Q
The modem can be programmed to check for a password on an incoming call. If the correct  
password is not provided the modem will hang up on the incoming call. If several unsuccessful  
incoming call attempts are received in a set time period, the modem will lock out future incoming  
calls for a user-set number of hours.  
Q
When an incoming call is successfully connected, the control of communications is passed to the  
calling software program. The modem will respond to computer commands to download data or  
other actions authorized by the meter passwords.  
Refer to the Communicator EXT Software Manual for instructions on programming the modem.  
2.4.3: Dial-Out Function  
Q
The Dial-Out Function (INP2) is intended to allow the meter to automatically report certain  
conditions without user intervention. The modem is normally polling the meter to determine if any  
abnormal or reportable conditions exist. The modem checks programmed meter conditions and  
programmed events (set in Nexus Communicator) to determine if a call should be placed.  
If any of the monitored events exist, the modem will automatically initiate a call to a specified  
location to make a report or perform some other function. For log full conditions, the meter will  
automatically download the log(s) that are nearing the full state.  
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2.5: Total Web Solutions  
Q
The 10/100BaseT Ethernet Option (INP 100) is a fully customizable web server that uses XML to  
provide access to real time data via Internet Explorer. EIG’s name for this dynamic system is Total  
Web Solutions. The system incorporates a highly programmable network card with built-in memory  
that is installed in the 100BaseT Option meters. Each card can be programmed to perform an  
extensive array of monitoring functions and the system is much faster than the 10BaseT Ethernet  
Option.  
NOTE: Nexus meters with the INP10 Option do not support Total Web Solutions.  
2.5.1: Hardware Overview  
Q
The Nexus 1250/1252 with the 10/100BaseT Ethernet Option (INP 100) has all the components of  
the standard Nexus 1250/1252 PLUS the capability of connection to a network through an Ethernet  
LAN or through the Internet via Modbus TCP, HTTP, SMTP, FTP and/or DHCP.  
Q
The Internal Network Option of the Nexus Meter is an extremely versatile communication tool.  
•
•
•
•
•
Adheres to IEEE 802.3 Ethernet standard using TCP/IP.  
Utilizes simple and inexpensive 100BaseT wiring and connections.  
Plugs right into your network using built-in RJ-45 jack.  
Programmable to any IP address, subnet mask and gateway requirements.  
Communicates using the industry standard Modbus/TCP protocol.  
2.5.2: Hardware Connection  
Q
Use Standard RJ-45 10/100BaseT cable to connect with the Nexus. The RJ-45 line is inserted into  
the RJ-45 Port on the face of the Nexus with IMP100 Ethernet Option.  
Q
To make the software connection, use the following steps.  
1. Using Port 1 or Port 4 (RS-485 connection), connect a PC to the meter. An RS-232/RS-485  
Converter may be required (Example: Electro Industries Unicom 2500).  
2. Double click on Communicator EXT Software to open.  
3. Click the Quick Connect or the Connection Manager icon in the icon tool bar. Click the  
Serial Port button. Make sure data matches the meter then click Connect.  
Q
Set the Network Settings using the following steps:  
(Refer to Section 3.6 of the Communicator EXT User Manual for more details).  
1. From the Device Profile screen, double-click on the Communications Ports line, then  
double-click on any of the ports. The Device Profile Communications Settings screen appears.  
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2. If you are going to use DHCP, click the Advanced Settings Button:  
Click the tab at the top of the DHCP screen. Click Enable.  
DHCP will automatically enter the IP Address and some or all of the Interface Settings.  
Click OK at the bottom of the screen to return to the Device Profile: Communication Ports  
screen. You may have to manually enter DNS, Email, Gateway Setting and/or a Unique  
Computer Name. Click OK.  
3. If you are NOT using DHCP, in the Network Settings section, enter data provided by your  
systems manager:  
IP Address:  
10.0.0.1  
255.255.255.0 (Example)  
0.0.0.0 (Example)  
NETWORK (Example)  
(Example)  
Subnet Mask:  
Default Gateway:  
Computer Name:  
Q
Q
Enter the Domain Name Server and Computer Name.  
Customize Web Content, if desired. Default Pages with an extensive array of readings comes with  
the meter. The content of the pages can be customized using FTP Client.  
From the Device Profile: Communications Ports screen, click Advanced Settings. Click the FTP  
Client tab on the top of the folder. Using FTP, you can easily replace any file by using the  
SAME FILE NAME as the one you want to replace.  
Q
Enter the Email Server IP Address. The Default Settings store ONE Email Server IP Address for  
administrative purposes or to send an alarm, if there is a problem. An ADDITIONAL 8 can be con-  
figured with FTP Client.  
Q
Q
Update FIRMWARE, if needed, with TFTP protocol (see Appendix C).  
After the above parameters are set, Communicator EXT will connect via the network using a Device  
Address of “1” and the assigned IP Address using the following steps:  
1. Double click on Communicator EXT icon to open.  
2. Click the Connect icon in the icon tool bar. The Connect screen will appear.  
3. Click the Network button at the top of the screen. The screen will change to one requesting the  
following information:  
Device Address:  
Host:  
1
IP Address (per your network administrator).  
Example: 10.0.0.1  
502  
Modbus TCP  
Network Port:  
Protocol:  
4. Click the Connect button at the bottom of the screen. Communicator EXT connects to the  
Nexus with the Host IP Address via the Network.  
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2.6: Measurements and Calculations  
The Nexus 1250/1252 Meter measures many different power parameters. The following is a list of the  
formulas used to conduct calculations with samples for Wye and Delta services.  
Samples for Wye: v , v , v , i , i , i , i  
an bn cn a b c n  
Samples for Delta: v , v , v , i , i , i  
ab bc ca a b c  
Q
Root Mean Square (RMS) of Phase to Neutral Voltages: n = number of samples  
For Wye: x = an, bn, cn  
n
v2  
∑
x
(
t
)
t=  
1
VRMS  
=
x
n
Q
Root Mean Square (RMS) of Currents: n = number of samples  
For Wye: x=a, b, c, n  
For Delta: x = a, b, c  
n
i2  
∑
x
(
t
)
t=  
1
IRMS  
=
x
n
Q
Root Mean Square (RMS) of Phase to Phase Voltages: n = number of samples  
For Wye: x, y= an, bn or bn, cn or cn, an  
n
2
(v  
−
vy  
)
∑
x
(
t
)
(
t
)
t=  
1
VRMS  
=
xy  
n
For Delta: xy = ab, bc, ca  
n
v2  
∑
xy  
(
t
)
t=  
1
VRMS  
=
xy  
n
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Q
Power (Watts) per phase:  
For Wye: x = a, b, c  
n
v
xn(t) •ix(t)  
∑
t
=1  
WX =  
n
Q
Q
Q
Apparent Power (VA) per phase:  
For Wye: x = a, b, c  
VAx  
=
V
•
I
RMSXN  
RMSX  
Reactive Power (VAR) per phase:  
For Wye: x = a, b, c  
VARx  
=
VAx2  
−
Wattx2  
Power (Watts) Total:  
For Wye:  
WT  
=
Wa  
+
Wb  
+
Wc  
For Delta:  
n
(v  
•iA − vBC •iC )  
∑
AB(t )  
(t )  
(t )  
(t )  
t=  
1
WT =  
n
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Q
Reactive Power (VAR) Total:  
For Wye:  
VART =VARA +VARB +VARC  
For Delta:  
2
n
⎡
⎢
⎢
⎢
⎤
⎥
⎥
⎥
v
v
) •iA  
∑
AB  
(
t
(
t
)
2
t=  
1
VART (VRMS • IRMS ) −  
AB  
A
n
⎢
⎣
⎥
⎦
+
2
n
⎡
⎢
⎢
⎢
⎤
) •iC  
∑
BC  
(
t
(
t
)
⎥
⎥
⎥
2
t=  
1
(VRMS • IRMS ) −  
BC  
C
n
⎢
⎣
⎥
⎦
Q
Apparent Power (VA) Total:  
For Wye:  
VAT =VAA +VAB +VAC  
For Delta:  
VAT  
=
WT2 VART2  
+
Q
Power Factor (PF):  
For Wye: x = A, B, C, T  
For Delta: x = T  
Wattx  
PFx  
=
VAx  
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Q
Phase Angles:  
1
∠ = cos− (PF)  
Q
% Total Harmonic Distortion (%THD):  
For Wye: x = V , V , V , I , I , I  
AN BN CN A B C  
For Delta: x = I , I , I , V , V , V  
A B C AB BC CA  
127  
(RMS )2  
∑
xh  
h=  
2
THD =  
RMSx  
1
Q
K Factor: x = I , I , I  
A B C  
127  
(h• RMS )2  
∑
xh  
h=  
1
KFactor =  
127  
(RMS )2  
∑
xh  
h=1  
Q
Watt hour (Wh):  
n
WT  
(
t
)
Wh  
=
∑
3600  
t=  
1
sec/hr  
Q
VAR hour (VARh):  
n
VART  
(
t
)
VARh  
=
∑
3600  
t=  
1
sec/hr  
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2.7: Demand Integrators  
Power utilities take into account both energy consumption and peak demand when billing customers.  
Peak demand, expressed in kilowatts (kW), is the highest level of demand recorded during a set period  
of time, called the interval. The Nexus 1250/1252 supports the following most popular conventions for  
averaging demand and peak demand: Thermal Demand, Block Window Demand, Rolling Window  
Demand and Predictive Window Demand. You may program and access all conventions concurrently  
with the Communicator EXT software (see the Communicator EXT User Manual).  
Q
Thermal Demand: Traditional analog watt-hour (Wh) meters use heat-sensitive elements to  
measure temperature rises produced by an increase in current flowing through the meter. A pointer  
moves in proportion to the temperature change, providing a record of demand. The pointer remains  
at peak level until a subsequent increase in demand moves it again, or until it is manually reset. The  
Nexus 1250/1252 mimics traditional meters to provide Thermal Demand readings.  
Each second, as a new power level is computed, a recurrence relation formula is applied. This  
formula recomputes the thermal demand by averaging a small portion of the new power value with a  
large portion of the previous thermal demand value. The proportioning of new to previous is  
programmable, set by an averaging interval. The averaging interval represents a 90% change in  
thermal demand to a step change in power.  
Q
Block (Fixed) Window Demand: This convention records the average (arithmetic mean) demand  
for consecutive time intervals (usually 15 minutes).  
Example: A typical setting of 15 minutes produces an average value every 15 minutes (at 12:00,  
12:15. 12:30. etc.) for power reading over the previous fifteen minute interval (11:45-12:00, 12:00-  
12:15, 12:15-12:30, etc.).  
Q
Rolling (Sliding) Window Demand: Rolling Window Demand functions like multiple overlapping  
Block Window Demands. The programmable settings provided are the number and length of  
demand subintervals. At every subinterval, an average (arithmetic mean) of power readings over the  
subinterval is internally calculated. This new subinterval average is then averaged (arithmetic  
mean), with as many previous subinterval averages as programmed, to produce the Rolling Window  
Demand.  
Example: With settings of 3 five-minute subintervals, subinterval averages are computed every 5  
minutes (12:00, 12:05, 12:15, etc.) for power readings over the previous five-minute interval (11:55-  
12:00, 12:00-12:05, 12:05-12:10, 12:10-12:15, etc.). Further, every 5 minutes, the subinterval aver-  
ages are averaged in groups of 3 (12:00. 12:05, 12:10, 12:15. etc.) to produce a fifteen (5x3) minute  
average every 5 minutes (rolling (sliding) every 5 minutes) (11:55-12:10, 12:00-12:15, etc.).  
Q
Predictive Window Demand: Predictive Window Demand enables the user to forecast average  
demand for future time intervals. The Nexus uses the delta rate of change of a Rolling Window  
Demand interval to predict average demand for an approaching time period. The user can set a relay  
or alarm to signal when the Predictive Window reaches a specific level, thereby avoiding  
unacceptable demand levels. The Nexus 1250/1252 calculates Predictive Window Demand using the  
following formula:  
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Example: Using the previous settings of 3 five-minute intervals and a new setting of 120%  
prediction factor, the working of the Predictive Window Demand could be described as follows:  
At 12:10, we have the average of the subintervals from 11:55-12:00, 12:00-12:05 and 12:05-12:10.  
In five minutes (12:15), we will have an average of the subintervals 12:00-12:05 and 12:05-12:10  
(which we know) and 12:10-12:15 (which we do not yet know). As a guess , we will use the last  
subinterval (12:05-12:10) as an approximation for the next subinterval (12:10-12:15). As a further  
refinement, we will assume that the next subinterval might have a higher average (120%) than the  
last subinterval. As we progress into the subinterval, (for example, up to 12:11), the Predictive  
Window Demand will be the average of the first two subintervals (12:00-12:05, 12:05-12:10), the  
actual values of the current subinterval (12:10-12:11) and the predistion for the remainder of the  
subinterval, 4/5 of the 120% of the 12:05-12:10 subinterval.  
# of Subintervals = n  
Subinterval Length = Len  
Partial Subinterval Length = Cnt  
Prediction Factor = Pct  
Sub  
Sub  
Sub  
...  
Partial  
Cnt  
Predict  
Len  
n
1
0
Len  
Len  
Len  
Len  
−1  
Value  
∑
i
i
=0  
Sub =  
Len  
Cnt−  
1
Value  
∑
i
i=  
0
Partial  
=
Cnt  
n−  
2
⎡
⎢
⎤
⎥
⎥
⎥
Value  
∑
i
⎡
⎤
⎥
⎦
⎡
Len  
−
Cnt  
⎤
⎡
⎤
i=  
0
⎢
⎢
Partial  
+
+
×
1
−
×
×
×
Pct  
Pct  
⎢
⎣
⎢
⎣
⎥
⎦
⎢
⎣
⎥
⎦
n
Len  
⎢
⎣
⎥
⎦
n−  
2
⎡
⎢
⎢
⎢
⎤
⎥
⎥
⎥
Sub  
∑
i
Sub0  
−
Subn−  
1
⎡
Len  
−
Cnt  
⎤
⎡
⎤
i=  
0
+
⎢
⎣
⎥
⎦
⎢
⎣
⎥
⎦
n
−
1
2x(n  
−
1)  
Len  
⎢
⎣
⎥
⎦
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2.8: Nexus External I/O Modules (Optional)  
The following multiple analog or digital I/O modules mount externally to the Nexus 1250/1252 Monitor.  
The Nexus 1250/1252 Monitor supports up to four I/O modules using internal power. Use the additional  
power supply, EIG PSIO, to extend I/O capability. See section 3.4 for mounting diagrams. See Chapter  
9 for details on installation and usage of the Nexus External I/O Modules.  
Q
Analog Transducer Signal Outputs (Up to two modules can be used with the Nexus 1250/1252.)  
•
•
•
•
1mAON4: 4 Analog Outputs, self powered, scalable, bidirectional.  
1mAON8: 8 Analog Outputs, self powered, scalable, bidirectional.  
20mAON4: 4 Analog Outputs, self powered, scalable.  
20mAON8: 8 Analog Outputs, self powered, scalable.  
Q
Analog Transducer Inputs (Multiple modules can be used.)  
•
•
•
•
8AI1: 8 Analog Inputs 0–1mA, scalable and bidirectional.  
8AI2: 8 Analog Inputs 0–20mA, scalable.  
8AI3: 8 Analog Inputs 0–5V DC.  
8AI4: 8 Analog Inputs 0–10V DC.  
Q
Q
Q
Q
Digital Dry Contact Relay Outputs (Multiple modules can be used.)  
4RO1: 4 Relay Outputs 10 Amps, 125V AC, 30V DC, Form C.  
•
Digital Solid State Pulse Outputs (Multiple modules can be used.)  
4PO1: 4 Solid State Pulse Outputs, Form A KYZ pulses.  
•
Digital Inputs (Multiple modules can be used.)  
8DI1: 8 Digital status inputs Wet/Dry Auto Detect, up to 300V AC/DC.  
•
Other I/O Accessories  
•
PSIO: Additional power supply for up to six I/O modules. This unit is necessary if you are  
connecting more than four I/O modules to a Nexus 1250/1252 Monitor.  
MBIO: Bracket for surface-mounting I/O modules to any enclosure.  
•
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2.9: Nexus 1250/1252 Meter Specifications  
Specification  
Nexus Meter  
Option D: 24V DC (-20%) – 48V DC (+20%)  
Option D2: 120V AC/DC (-20%) – 230V AC (+20%)  
150 Volts Phase to Neutral (Standard; for use with PTs)  
300 Volts Phase to Neutral (Option -G)  
10A Maximum (Programmable to any CT Ratio)  
Current: Continuous 200% Rated  
Control Power Requirements  
Input Voltage Range  
Input Current Range  
Input Withstanding Capabilities  
Current: Surge 10x maximum input for 3 seconds  
Surge Withstanding Per IEEE C37.90.1  
Voltage: 0.05VA @ 120V rms  
Burden  
Current: 0.002VA @ 5A rms  
I/O Isolation  
Sensing Method  
Update Time  
2500V DC, 60 Hz  
RMS  
90 msec  
Fundamental 20–65 Hz  
Frequency Range  
Up to 83rd Harmonic Measuring Capability  
3.4 x 7.3 x 10.5 inches / 8.6 x 18.5 x 26.6 centimeters  
40 watts (with optional modules and display)  
Approximately 12 watts (without optional modules and display)  
-40°C to +80°C / -40°F to +176°F  
15–20 V DC at 50–200mA  
Dimensions (HxWxL)  
Maximum Power Consumption  
Nominal Power Consumption  
Operating Temperature  
Auxiliary Output Power Voltage  
Maximum Auxiliary Power Current 1.6A (short protected)  
1244*  
UL Listing  
*Not evaluated for accuracy, reliability or capability to perform intended function.  
Flicker (1252)  
Evaluation per IEC 61000-4-15  
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2.10: Nexus P40N, P41N, P43N LED External Display Specifications  
Specification  
Nexus P40N, P41N, P43N LED External Display  
Maximum Input Voltage  
30V DC  
7V DC  
Minimum Input Voltage  
Maximum Power Consumption  
Nominal Power Consumption  
Operating Temperature Range  
Overall Dimensions (HxWxL)  
8 Watts  
Approximately 6 Watts  
-40°C to + 80°C / -40°F to +176°F  
2.2 x 4.4 x 4.4 in / 5.9 x 11.1 x 11.1 cm  
2.11: Nexus P60N Touch Screen Display Specifications  
Specification  
Nexus P60N Touch Screen Display  
Maximum Input Voltage  
30V DC  
10V DC  
Minimum Input Voltage  
Maximum Power Consumption  
Nominal Power Consumption  
Operating Temperature Range  
Overall Dimensions (HxWxL)  
5 Watts  
Approximately 4.5 Watts  
0°C to + 50°C / +32°F to +122°F  
1.6 x 5.4 x 8.0 in / 4.0 x 13.7 x 20.3 cm  
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Chapter 3  
Hardware Installation  
3.1: Mounting the Nexus 1250/1252 Meter  
Q
The Nexus 1250/1252 Meter is designed to mount against any firm, flat surface. Use a #10 screw in  
each of the four slots on the flange to ensure that the unit is installed securely. For safety reasons,  
mount the Meter in an enclosed and protected environment, such as in a switchgear cabinet. Install  
a switch or circuit breaker nearby; label it clearly as the meter’s disconnecting mechanism.  
NOTE: The Nexus Meter with Internal Modem Option mounts the same way.  
Q
Maintain the following conditions:  
•
•
•
Operating Temperature: -40°C to +70°C / -40°F to +158°F  
Storage Temperature: -45°C to +85°C / -49°F to +185°F  
Relative Humidity: 5 to 95% non-condensing  
10.5” (26.67cm)  
2 x 3.25” (8.25cm)  
2x4.0” (10.16cm)  
7.25”  
(18.41cm)  
6.74”  
(17.11cm)  
4 x 0.221” (5.61mm) Thru Slot  
(For #10 Screw)  
Figure 3.1: Nexus Meter Mounting Diagram, Top View  
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Nexus Meter Mounting Diagram, Side View  
2.35” (5.96cm)  
3.40” (8.63cm) (MAX)  
Figure 3.2  
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3.2: Mounting the Nexus LED External Displays  
Q
The Nexus 1250/1252 LED Displays, Model # P40N, P41N and P43N, mount using a standard  
ANSI C39.1 drill plan.  
Q
Secure the four mounting studs to the back of the panel with the supplied nuts.  
Q
Six feet of RS-485 communication/power cable harness is supplied. Allow for at least a 1.25-inch  
(3.17cm) diameter hole in the back for the cable harness. See Chapter 5 for communication and  
power supply details.  
Q
The cable harness brings power to the display from the Nexus 1250/1252 Meter, which supplies  
15–20V DC. The P40N (or P41N or P43N) can draw up to 500 mA in display test mode.  
4.38”Sq.  
(11.12cm)  
.75” (19.05mm)  
1.438”  
(3.65cm)  
Nexus P40N Display, Side View  
Nexus P40N Display, Front View  
3.38” (8.58cm) Sq.  
4 X 0.198” (5.02mm)  
4.00” (10.16cm)  
+
ANSI C39.1 Drill Plan  
1.687” (14.28cm)  
Figure 3.3: Nexus P40N LED External Display Mounting Diagrams  
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3.3: Mounting the Nexus P60N Touch Screen External Display  
Figure 3.4: Nexus P60N Touch Screen Display Mounting Diagram  
Q
The Nexus 1250/1252 P60N Touch Screen Display mounts easily, using the diagrams above and on  
the next page. A bezel and a gasket are included with the P60N. Since the P60N employs an LCD  
display, the viewing angle must be considered when mounting. Install the P60N at a height and  
angle that make it easy for the operator to see and access the screen.  
Q
For optimum performance, maintain  
the following conditions where the  
Touch Screen Display is mounted:  
•
•
•
Operating Temperature: 0°C to  
+50°C / +32°F to +122°F  
Factory  
Test  
Connector  
Storage Temperature: -20°C to  
+70°C / -36°F to +158°F  
Relative Humidity: 25 to 65%  
non-condensing  
Connect  
to NEXUS  
Figure 3.5: Nexus P60N Back Detail  
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Figure 3.6: Cutout for Nexus P60N Touch Screen Display  
Q
Q
Q
To bezel mount the P60N, cut an opening in the mounting panel. Follow above cutout dimensions.  
Carefully “drop in” the P60N with bezel and gasket attached.  
Fasten the unit securely with the four 6-32 hex nuts supplied.  
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3.4: Mounting the Nexus External I/O Modules  
Q
Secure the mounting brackets to the I/O using the screws supplied (#440 pan-head screws). Next,  
secure the brackets to a flat surface using a #8 screw with a lock washer.  
Q
If multiple I/O modules are connected together, as shown in Figure 3.4, secure a mounting bracket to  
both ends of the group. One Nexus will supply power for up to four I/O modules. To connect more  
than four I/O modules, use an additional power supply, such as the EIG PSIO. Connect multiple I/O  
modules using the RS-485 side ports.  
Q
Six feet of RS-485 cable harness is supplied. The cable harness brings power to the display from the  
Nexus Meter, which supplies 15–20V DC at 50–200mA. See Chapter 5 for power supply and com-  
munication details.  
Mounting Bracket  
1.125” (2.85cm)  
2 x .625” (1.58cm)  
0.015” (.38mm)  
4.215” (10.70cm)  
Mounting Bracket  
Figure 3.7: Nexus I/O Modules Mounting Diagram, Overhead View  
Mounting Brackets (MBIO)  
Female RS-485 Side Port  
I/O Port  
Male RS-485 Side Port  
Figure 3.8: Nexus I/O Module Communication Ports  
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Nexus I/O Modules Mounting Diagram, Front View  
Mounting Bracket (MBIO)  
Mounting Bracket (MBIO)  
1.25” (3.17cm)+Y  
Per Module  
2.20” (5.58cm)  
3.41” (8.66cm)  
2x1.10” (2.79cm)  
Y
0.605” (1.53cm)  
1.235” (3.13cm)  
Figure 3.9  
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Chapter 4  
Electrical Installation  
4.1: Wiring the Monitored Inputs and Voltages  
Q
Select a wiring diagram from Section 4.8 that best suits your application. Wire the Nexus 1250/1252  
exactly as shown. For proper operation, the voltage connection must be maintained and must  
correspond to the correct terminal. Program the CT and PT Ratios in the Device Profile section of  
the Communicator EXT software; see the Communicator EXT User Manual for details.  
The cable required to terminate the voltage sense circuit should have an insulation rating greater than  
600V AC and a current rating greater than 0.1 Amp.  
Use a minimum of 14 AWG wire for all phase voltage and current connections.  
4.2: Fusing the Voltage Connections  
Q
For accuracy of the readings and for protection, EIG requires using 0.25-Amp rated fuses on all  
voltage inputs as shown in the wiring diagrams (see section 4.8).  
The Nexus Meter can handle a maximum voltage of 150V phase to neutral and 300V phase to phase.  
Potential Transformers (PTs) are required for higher voltages with the standard rating. With Option -  
G, the direct voltage input is extended to 300V phase to neutral and 600V phase to phase.  
4.3: Wiring the Monitored Inputs - VRef  
Q
The Voltage Reference connection references the monitor to ground or neutral.  
4.4: Wiring the Monitored Inputs - VAux  
Q
The Voltage Auxiliary connection is an auxiliary voltage input that can be used for any desired  
purpose, such as monitoring neutral to ground voltage or monitoring two different lines on a switch.  
4.5: Wiring the Monitored Inputs - Currents  
Q
Install the cables for the current at 600V AC minimum insulation. The cable connector should be  
rated at 10 Amps or greater and have a cross-sectional area of 14 AWG.  
Q
Mount the current transformers (CTs) as close as possible to the meter. The following table  
illustrates the maximum recommended distances for various CT sizes, assuming the connection is via  
14 AWG cable.  
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EIG Recommendations  
CT Size (VA)  
Maximum Distance from CT to Nexus (Feet)  
2.5  
5.0  
10  
15  
7.5  
30  
10.0  
15.0  
30.0  
40  
60  
120  
WARNING!!  
DO NOT leave the secondary of the CT open when primary current is flowing. This may  
cause high voltage, which will overheat the CT. If the CT is not connected, provide a  
shorting block on the secondary of the CT.  
Q
It is important to maintain the polarity of the CT circuit when connecting to the Nexus. If the  
polarity is reversed, the Nexus will not provide accurate readings. CT polarities are dependent upon  
correct connection of CT leads and the direction CTs are facing when clamped around the  
conductors. EIG recommends using shorting blocks to allow removal of the Nexus Meter from an  
energized circuit, if necessary. Shorting blocks are not required for proper meter operation.  
4.6: Isolating a CT Connection Reversal  
Q
For a WYE System, you may either:  
1. Check the current phase angle reading on the Nexus External Display (see Chapter 6). If it is  
negative, reverse the CTs.  
2. Or, go to the Phasors screen of the Communicator EXT software (see Communicator EXT  
User Manual). Note the Phase Relationship between the Current and Voltage; they should be in  
phase.  
Q
For a DELTA System:  
Go to the Phasors screen of the Communicator EXT software program. The current should be  
30 degrees off the phase-to-phase voltage.  
4.7: Instrument Power Connections  
Q
The Nexus requires a separate power source. To use AC power, connect the line supply wire to the  
L+ terminal and the neutral supply wire to the N- terminal on the Nexus. To use DC power, connect  
the positive supply wire to the L+ terminal and the negative (ground) supply wire to the N- terminal  
on the Nexus. Power supply options and corresponding suffixes are listed in the following table:  
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Control Power  
18-60 Volts DC  
Option Suffix  
D
90-276 Volts AC/DC  
D2  
Q
Q
Do not ground the unit through the negative of the DC supply. Separate grounding is required.  
Externally fuse the power supply with a 5 Amp fuse.  
4.8: Wiring Diagrams  
Q
Choose the diagram that best suits your application. Diagrams appear on the following pages. If the  
connection diagram you need is not shown, contact EIG for a custom Connection diagram.  
Q
NOTE: If you purchased a “G” Option Nexus for a 300 Volt secondary, be sure to enable the  
option on the CT and PT screen of the Communicator EXT software’s Device Profile (see the  
Communicator EXT User Manual for details).  
Figure #  
Description  
4.1  
4-Wire Wye, 3-Element Direct Voltage with 4 CTs  
4.2  
4.3  
4.4  
4.5  
4.6  
4.7  
4.8  
4-Wire Wye, 3-Element with 3 PTs and 4 CTs  
4-Wire Wye, 3-Element with 3 PTs and 3 CTs  
3-Wire, 2-Element Open Delta with 2 PTs and 3 CTs  
3-Wire, 2-Element Open Delta with 2 PTs and 2 CTs  
3-Wire, 2-Element Delta Direct Voltage with 3 CTs  
3-Phase, 4-Wire Wye, 2.5 Element with 2 PTs and 3 CTs  
4-Wire, 3-Element Grounded Delta with 4 CTs - G Option  
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0.25 A  
INPUT  
Figure 4.1: 4-Wire Wye, 3-Element Direct Voltage with 4 CTs  
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0.25A  
INPUT  
Figure 4.2: 4-Wire Wye, 3-Element with 3 PTs and 4 CTs  
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0.25 A  
INPUT  
Figure 4.3: 4-Wire Wye, 3-Element with 3 PTs and 3 CTs  
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0.25 A  
Figure 4.4: 3-Wire, 2-Element Open Delta with 2 PTs and 3 CTs.  
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0.25 A  
Figure 4.5: 3-Wire, 2-Element Open Delta with 2 PTs, 2 CTs.  
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0.25 A  
INPUT  
Figure 4.6: 3-Wire, 2-Element Delta Direct Voltage with 3 CTs.  
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0.25 A  
INPUT  
Figure 4.7: 3-Phase, 4-Wire Wye, 2.5 Element with 2 PTs, 3 CTs.  
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0.25 A  
INPUT  
Figure 4.8: 4-Wire, 3-Element Grounded Delta with 4 CTs - G Option.  
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Chapter 5  
Communication Wiring  
5.1: Communication Overview  
ꢀ
RS-232 communication is used to connect a single Nexus 1250/1252 Meter with another device,  
such as a computer, RTU or PLC. The link is viable for a distance up to 50 feet (15.2 m) and is  
available only through the Nexus 1250/1252 Meter’s Port 1. You must set the selector switch beneath  
the port to RS-232 (see Figure 5.3).  
ꢀ
RS-485 communication allows multiple Nexus Meters to communicate with another device at a local  
or remote site. The I/O modules and the Nexus Display use RS-485 to communicate with the Nexus  
Meter. All RS-485 links are viable for a distance up to 4000 feet (1220 m). Ports 1 through 4 on the  
Nexus 1250/1252 Meter are two-wire, RS-485 connections operating up to 115,200 baud. To use  
Port 1 for RS-485, set the selector switch to RS-485 (see Figure 5.3).  
1 device, 50 feet maximum, Nexus Port 1  
RS-232  
RS-485  
Nexus  
RS-232/485  
RS-232  
Converter  
Nexus  
Nexus  
Nexus  
(Unicom 2500)  
Up to 31 Devices, 4000 feet maximum (without a  
repeater), connected in series via RS-485 (daisy chain)  
MODEM  
RS-232  
Nexus  
Null Modem  
Telephone Line,  
Fiber Optic Link or  
Radio Link  
MODEM  
RS-485  
RS-232/485 Converter  
(Modem Manager)  
RS-232  
Nexus  
Nexus  
Nexus  
Figure 5.1: Communication Overview  
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ꢀ
RJ-11 Telephone Line allows a Nexus Meter with the Internal Modem Option to communicate with  
a PC. No other hardware is necessary for this easy-to-use connection. The Nexus 1250/1252 Meter  
with the Internal Modem Option can connect via RS-485 to other Nexus Meters in local or remote  
sites in a daisy chain configuration, as depicted below.  
The Nexus Meter with the Internal Modem Option has a unique label; Port 2 is labeled Modem  
Gateway. If you are going to use RS-485 to connect multiple Nexus 1250/1252 meters, you MUST  
use the Modem Gateway. For more details, see Chapter 10 of this manual.  
RS-485  
RJ-11  
Daisy Chain  
Originate Modem  
(or Internal to PC)  
PC  
Figure 5.2: RJ-11 Communication with Internal Modem Option  
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ꢀ
RJ-45 Network Connection allows a Nexus Meter with the Internal Network Option to  
communicate with multiple PC’s concurrently. No other hardware is necessary for this easy-to-use  
connection. The Nexus Meter with the Internal Network Option can connect via RS-485 to other  
Nexus Meters in local or remote sites in a daisy chain configuration, as depicted below.  
The Nexus 1250/1252 Meter with the Internal Network Option has a unique label; Port 2 is labeled  
Ethernet Gateway. If you are going to use RS-485 to connect multiple Nexus meters via the net-  
work, you MUST use the Ethernet Gateway. For more details, see Chapter 11 of this manual.  
10/100BaseT  
or 10BaseT  
RJ-45  
RS-485  
MODBUS/RTU  
MODBUS/TCP  
over Ethernet  
Daisy Chain  
Network  
Figure 5.3: RJ-45 Communication with Internal Network Option  
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For all communications: S=Shield. This connection is  
used to reference the Nexus port to the same  
potential as the source. It is not an earth-ground  
connection. You must also connect the shield to  
earth-ground at one point.  
I/O Modules and Display  
require power connections  
to the +/- voltage terminals  
(dashed lines).  
RS-232 Extension  
Cable  
(1 to 1 wiring)  
RS-485 Master  
Unicom or Modem Manager  
Nexus P40N External Display  
Nexus I/O Module  
–
–
+
+
G
A(+) B(-) S - V +  
A(+) B(-) S - V +  
R
R
T=  
T=  
~120 Ohms  
~120 Ohms  
R
T=  
~120 Ohms  
R
R
R
T=  
T=  
T=  
~120 Ohms  
~120 Ohms  
~120 Ohms  
+ V - S B(-) A(+)  
+ V - S B(-) A(+)  
+ V - S B(-) A(+) + V - S B(-) A(+)  
8
7
6
5
4
3
2
1
C
-
+
Port 1  
Port 2  
Port 3  
Port 4  
High Speed Inputs  
IRIG-B  
RS-232 or  
Normally Slave  
RS-485 (Set)  
Modem/Ethernet Gateway  
RS-485  
RS-232  
NOTE: You may use ANY port to connect a Nexus Display or RS-485 Master. However, if you are using  
the Internal Modem (or Network) Option, Port 2 is labeled Modem (Ethernet) Gateway. Ports 1, 3 and 4 DO  
NOT change. The I/O Modules MUST use Port 4 (Port 3 is an alternate).  
Nexus P40N, P41N or P43N Display is shipped programmed to use Port 3—see section 5.7 for details.  
Figure 5.4: Communication Wiring  
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5.2: RS-232 Connection—Nexus Meter to a Computer  
ꢀ
Use Port 1 for RS-232 communication. Set the selector switch beneath the port to RS-232.  
ꢀ
Insert one end of an RS-232 extension cable into the Nexus Meter’s 9-pin female serial port. Insert  
the opposite end into a port on the computer.  
ꢀ
The RS-232 standard limits the cable length to 50 feet (15.2m).  
ꢀ
The RS-232 Port is configured as Data Communications Equipment (DCE).  
Nexus Meter Port 1  
RS-232 Port  
Pin #2=Transmit  
Pin #3=Receive  
Pin #5=Ground  
RS-485 Port  
(see Section 5.3 for details)  
+ V -  
S
B(-) A(+)  
5
4
3
2
1
Switch set for RS-232 communication  
9
8
7
6
RS-232  
RS-485  
Figure 5.5: Nexus Port 1—RS-232/RS-485 Communication  
5.3: Nexus RS-485 Wiring Fundamentals (with R Explanation)  
T
Nexus RS-485 Ports (Ports 1–4) (see Figure 5.5 above)  
+V-  
S
Voltage terminals for power connections: Use with Nexus I/O Modules and the  
Nexus Displays only. The Nexus 1250/1252 Meter supplies 17V DC through the +V- ter-  
minal connections. Note: Do not connect these pins to devices that receive power from  
another source—ie, a computer—or to devices that do not require power to operate.  
Shield: The Shield connection is used to reference the Nexus port to the same  
potential as the source. It is not an earth-ground connection. You must also connect  
the shield to earth-ground at one point. Do not connect the shield to ground at  
multiple points; it will interfere with communication.  
A(+)/B(-)  
Two-wire, RS-485 communication terminals: Connect the A(+) terminal of the Nexus  
Port to the (+) terminal of the device. Connect the B(-) terminal of the Nexus Port to the  
(-) terminal of the device.  
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ꢀ
RS-485 communication allows multiple devices to communicate on a bus. The Nexus 1250/1252  
Ports 1 to 4 are RS-485 terminals, viable for a distance of up to 4000 feet (1219 m). (Nexus’ Port 1  
can be switched between RS-232 and RS-485.) Below is a detail of a 2-wire RS-485 port.  
2-Wire RS-485 Port  
S - +  
Shield  
Twisted  
Pair  
.
Connect (-) to (-) of  
next device  
.
Connect (+) to (+) of  
next device  
.
.
.
Figure 5.6: 2-Wire RS-485 Port Detail  
For All RS-485 Connections:  
Use a shielded twisted pair cable 22 AWG (0.33 mm2) or larger, grounding the shield at one end  
only.  
ꢀ
ꢀ
Establish point-to-point configurations for each device on a RS-485 bus: Connect (+) terminals to  
(+) terminals; connect (-) terminals to (-) terminals.  
ꢀ
ꢀ
Protect cables from sources of electrical noise.  
Avoid both “star” and “tee” connections (see Figure 5.7). No more than two cables should be  
connected at any one point on an RS-485 network, whether the connections are for devices,  
converters or terminal strips.  
ꢀ
ꢀ
Include all segments when calculating the total cable length of a network. If you are not using an  
RS-485 repeater, the maximum length for cable connecting all devices is 4000 feet (1219 meters).  
RT EXPLANATION:  
Termination Resistors are generally used on both ends of longer length transmission lines.  
The value of the Termination Resistors is determined by the electrical parameters of the cable.  
Use RTs only on Master and Last Slave when connecting multiple meters in a Daisy Chain.  
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Incorrect Connection: “T”  
“Tee” Connection Incorrect!  
The three wires connected in a  
“T” shape on both the (+) and  
(-) terminals will cause interfer-  
ence problems.  
RS-485 Port  
Incorrect Connection: “Star”  
“Star” Connection Incorrect!  
The three wires connected in a  
“Star” shape on both the (+)  
and (-) terminals will cause  
interference problems.  
RS-485 Ports  
Figure 5.7: Incorrect “T” and “Star” Topologies  
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5.4: RS-485 Connection—Nexus Meter to a Computer or PLC  
ꢀ
Use any Port on the Nexus 1250/1252. If you use Port 1, set the selector switch beneath the port to  
RS-485 (see Figure 5.3).  
ꢀ
The link using RS-485 is viable for up to 4000 feet (1219 meters).  
ꢀ
You must use an RS-485 to RS-232 converter, such as EIG’s Unicom 2500. See sections 5.7.1.  
ꢀ
For information on connecting the Nexus Meter to a modem, see sections 5.14–5.16.  
ꢀ
Do not use the V(+)/V(-) pins; they supply power to the Nexus Displays and Nexus I/O Modules.  
5.5: RJ-11 (Telephone Line) Connection—Nexus with Internal Modem Option  
to a PC  
ꢀ
Use RJ-11 Standard Telephone Line to connect with the Nexus 1250/1252. The RJ-11 line is  
inserted into the RJ-11 Port on the face of the Nexus with Internal Modem Option.  
ꢀ
The length of the connection using RJ-11 into the Nexus 1250/1252 is virtually unlimited.  
ꢀ
To connect with other Nexus 1250/1252 Meters in either local or remote locations, you MUST use  
Port 2 as a Master and an RS-485 connection.  
ꢀ
The link using RS-485 is viable for up to 4000 feet (1219 meters).  
ꢀ
For more information on the Nexus Meter with the Internal Modem Option, see Chapter 10 of this  
manual.  
5.6: RJ-45 Connection—Nexus with Internal Network Option to multiple PC’s  
ꢀ
The Internal Network Option conforms to the IEEE 802.3, 10BaseT specification using unshielded  
twisted pair (UTP) wiring. This allows the use of inexpensive RJ-45 connectors and CAT 3 or better  
cabling.  
ꢀ
Using this LAN connection allows multiple PC’s to be connected concurrently. The RJ-45 line is  
inserted into the RJ-45 Port on the face of the Nexus with Internal Network Option.  
ꢀ
The connection using RJ-45 into the Nexus 1250/1252 can connect the Nexus to a network using  
Modbus/TCP protocol over Ethernet.  
ꢀ
To connect with other Nexus Meters in either local or remote locations, you MUST use Port 2  
(which is labeled Ethernet Gateway) as a Master and an RS-485 connection. The link using RS-485  
is viable for up to 4000 feet (1219 meters).  
ꢀ
For more information on the Nexus 1250/1252 Meter with the Internal Network Option, see Chapter  
11 of this manual.  
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5.7: RS-485 Connection—Nexus to an RS-485 Master (Unicom or Modem  
Manager)  
ꢀ
To establish communication between a Nexus Meter and any RS-485 master, such as EIG’s Unicom  
2500, Modem Manager or other RS-232–485 converter, use a shielded, twisted pair cable.  
ꢀ
Use an RS-485 port (Ports 1–4) on the Nexus Meter. If you use Port 1, set the selector switch  
beneath it to RS-485 (see Figure 5.3). Connect the A(+) and B(-) terminals on the Nexus to the (+)  
and (-) terminals on the master. Provide jumpers on the master, linking its two (-) terminals and two  
(+) terminals. RS-485 communication is viable for up to 4000 feet (1219 meters).  
ꢀ
Connect the shield to the Ground (G) terminal on the Master. The (S) terminal on the Nexus is used  
to reference the Nexus port to the same potential as the source. It is not an earth ground connection.  
You must also connect the shield to earth-ground at one point.  
NOTE: Refer to section 5.3 for information on using RTs.  
5.7.1: Using the Unicom 2500  
The Unicom 2500 provides RS-485/RS-232 conversion. In doing so it allows the Nexus to  
communicate with a PC or other device. See the Unicom 2500 Installation and Operation Manual  
for additional information.  
Figures 5.8 and 5.9, on the next page, illustrate the Unicom 2500 connections for RS-485.  
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Figure 5.9: Detail of “Jumpers”  
Figure 5.8: Unicom 2500 with Connections  
The Unicom 2500 can be configured for either 4-wire or 2-wire RS-485 connections. Since the  
Nexus uses a 2-wire connection, you need to add jumper wires to convert the Unicom 2500 to  
the 2-wire configuration.  
As shown in Figure 5.9, you connect the "RX-" and "TX-" terminals with a jumper wire to make  
the "-" terminal, and connect the "RX+" and "TX+" terminals with a jumper wire to make the "+"  
terminal  
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5.8: RS-485 Connection—Nexus Meter to the Nexus P40N External Display  
ꢀ
Insert one end of the supplied RS-485 cable into Port 3 of the Nexus 1250/1252 Meter. Port 3 is  
factory-set to match the Nexus Display’s baud rate of 9600. To use a port other than Port 3, you must  
set the port’s baud rate to 9600 using the Communicator EXT software (see the Communicator EXT  
User Manual). Insert the other end of the cable into the back of the Nexus P40N, P41N or P43N  
Display. The connectors fit only one way into the ports.  
ꢀ
The cable harness brings 17V DC to the displays from the Nexus 1250/1252 Meter, represented by  
dashed lines in the figure below. RS-485 communication is viable for up to 4000 feet (1219 meters).  
If your cable length exceeds 200 feet you must use a remote power supply, such as EIG’s PSIO, and:  
•
Connect the shield to the shield (S) terminal on the Nexus Display port. The (S) terminal on the  
Nexus is used to reference the Nexus port to the same potential as the source. It is not an  
earth-ground connection. You must also connect the shield to earth-ground at one point.  
•
Provide termination resistors at each end, connected to the A(+) and B(-) lines. RT is  
approximately 120 Ohms. NOTE: Refer to section 5.3 for RT Explanation.  
Nexus P40N, P41N or P43N Display Port  
A(+) B(-) S - V +  
R
Nexus P40N, P41N or P43N  
Display, Back View  
T
Top  
V+  
V-  
S
B(-)  
A(+)  
Bottom  
R
T
+ V - S B(-) A(+)  
Nexus Meter Port 3  
Figure 5.10: Nexus Meter Connected to Nexus P40N, P41N or P43N External Display  
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5.9: RS-485 Connection—Nexus Meter to the Nexus P60N External Display  
ꢀ
To connect the Nexus P60N Touch Screen External Display, use the Stand Alone Interface Cable  
provided with the display. The cable is six (6) feet long with 20 AWG conductors (see detail  
below). Insert one end of the supplied cable into Port 3 of the Nexus 1250/1252 Meter. Port 3 is  
factory-set to match the Nexus Display’s baud rate of 9600. To use a port other than Port 3, you  
must set the port’s baud rate to 9600 using the Communicator EXT software (see the  
Communicator EXT User Manual). Insert the other end of the cable into the back of the Nexus  
P60N Display. The connectors fit only one way into the ports.  
Nexus P60N Display Port  
Stand Alone Interface Cable  
Nexus P60N Display, Back View (Detail)  
Top  
Factory Test  
Connector  
Bottom  
P60N Connection Color Key  
LCD  
Nexus  
V+  
Color  
Red  
Pattern  
5 DCIN  
(12-30V DC)  
4 (GND)  
V-  
Black  
3 (485+)  
2 (485-)  
1 (GND)  
A(+)  
B(-)  
S
White  
Black  
Silver  
Nexus Meter Port 3  
Figure 5.11: Nexus Meter Connected to Nexus P60N Touch Screen Display  
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5.10: Communication Ports on the Nexus I/O Modules  
ꢀ
Female RS-485 Side Port: use to connect to another module’s female RS-485 side port.  
ꢀ
Male RS-485 Side Port: use to connect to the Nexus Meter’s Port 4 (see section 5.8) or to connect  
to another module’s male RS-485 side port.  
ꢀ
I/O Port: use for functions specific to the type of module; size and pin configuration varies  
depending on type of module. For more detail, refer below to section 5.11 and to Chapter 9 of this  
manual.  
Mounting Brackets  
Female RS-485 Side Port  
LEDs  
I/O Port  
(Size and pin  
configuration vary)  
Male RS-485 Side Port  
Figure 5.12: Communication Ports on the Nexus I/O Modules  
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5.11: RS-485 Connection—Nexus Meter to Nexus I/O Modules  
ꢀ
Six feet of RS-485 cable harness is supplied. Insert one end of the cable into Port 4 of the Nexus  
1250/1252 Meter.  
ꢀ
Insert the other end of the cable into the I/O module’s female RS-485 side port (see Figure 5.9). The  
connectors fit only one way into the ports.  
ꢀ
Use the male RS-485 side port to attach another I/O module. The Nexus 1250/1252 will power up to  
four connected I/O modules using 15–20V DC at 50–200mA, represented by dashed lines in the  
figure below. Use the steps below (section 5.12) to determine if you must use a separate power  
source (for example, EIG PSIO) to supply added power to the group. RS-485 communication is  
viable for up to 4000 feet (1219 meters). However, if your cable length exceeds 200 feet, use the  
remote power supply and:  
•
Connect the A(+) and B(-) terminals on the Nexus to the A(+) and B(-) terminals of the female  
RS-485 port. Connect the shield to the shield (S) terminal. The (S) terminal on the Nexus 1250/  
1252 is used to reference the Nexus port to the same potential as the source. It is not an earth  
ground connection. You must also connect the shield to earth-ground at one point.  
•
Provide termination resistors at each end, connected to the A(+) and B(-) lines. RT is  
approximately 120 Ohms. NOTE: Refer to section 5.3 for RT Explanation.  
A(+) B(-) S - V +  
Male Side Port on Nexus I/O Module  
R
T
R
T
Nexus Meter Port 4  
+ V- S B(-) A(+)  
Figure 5.13: Nexus Meter Connected to Nexus I/O Module  
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5.12: Steps to Determine Power Needed  
•
•
•
•
Available power for All Ports of the Nexus 1250/1252 is 12 VA.  
Refer to the table below to determine the VA Ratings for I/O modules and displays.  
Add together the VA Ratings for I/Os and Displays in use.  
Compare Available Power to Power Needed to determine if you must use an additional  
power source. EIG recommends the PSIO 12V power source. See section 9.2.1.  
5.13: I/O Modules’ Factory Settings and VA Ratings  
ꢀ
All I/Os are shipped pre-programmed with a baud rate of 57600 and addresses. The table below  
details the factory-set address for each module and the VA Ratings for I/O modules and Nexus  
displays. Refer to the previous section (section 5.12) for the steps to determine if you must use an  
additional power source. For programming, refer to Chapter 8 of the Communicator EXT User  
Manual.  
I/O MODULES’ FACTORY SETTINGS AND VA RATINGS  
MODEL NUMBER  
1mAON4  
1mAON8  
20mAON4  
20mAON8  
8A11  
MODULE  
ADDRESS  
128  
VA RATING  
2.7 VA  
3.2 VA  
5.0 VA  
8.5 VA  
2.3 VA  
2.3 VA  
2.3 VA  
2.3 VA  
2.7 VA  
2.7 VA  
1.0 VA  
0-1mA, 4 Analog Outputs  
0-1mA, 8 Analog Outputs  
4-20mA, 4 Analog Outputs  
4-20mA, 8 Analog Outputs  
0-1mA, 8 Analog Outputs  
0-20mA, 8 Analog Outputs  
0-5V DC, 8 Analog Outputs  
0-10V DC, 8 Analog Outputs  
4 Latching Relay Outputs  
4 KYZ Pulse Outputs  
128  
132  
132  
136  
8A12  
140  
8A13  
144  
8A14  
148  
4RO1  
156  
4PO1  
160  
8D11  
8 Status Inputs (Wet/Dry)  
164  
NEXUS DISPLAYS’ VA RATINGS  
Nexus LED Display  
P40N, P41N or P43N  
P60N  
8 VA  
5 VA  
Nexus Touch Screen Display  
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5.14: Linking Multiple Nexus Devices in Series  
ꢀ
You may connect a total of 31 Nexus 1250/1252 Meters in series on a single bus using RS-485. The  
cable length may not exceed 4000 feet (1219 meters). Before assembling the bus, each Nexus Meter  
must be assigned a unique address; see the Communicator EXT User Manual.  
ꢀ
Connect the A(+) and B(-) terminals of each Nexus Meter. Use jumpers on any RS-485 Master  
connected at the end of the chain (see section 5.5).  
ꢀ
Connect the shield to the (S) terminal on each Nexus and to the Ground on the RS-485 Master. This  
connection is used to reference the Nexus port to the same potential as the source. It is not an earth  
ground connection. You must also connect the shield to earth-ground at one point.  
ꢀ
Provide resistors at each end, connected to the (+) and (-) lines. RT is approximately 120 Ohms, but  
this value may vary based on length of cable run, gauge or the impedance of the wire.  
NOTE: Refer to section 5.3 for RT Explanation.  
Up to 31 Nexus 1250/1252 Meters Maximum  
RS-485 to RS-232  
Converter (RS-485 Master)  
Nexus RS-485 Port  
Nexus RS-485 Port  
GND TX- RX- TX+ RX+  
+ V - S B(-) A(+)  
+ V - S B(-) A(+)  
+ V - S B(-) A(+)  
Jumpers  
R
R
T
Figure 5.14: Linking Multiple Nexus Devices in Series  
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5.15: Networking Groups of Nexus Meters  
ꢀ
You may connect up to 31 Nexus 1250/1252 Meters on the same RS-485 bus. Each one must be  
assigned a unique address; see the Communicator EXT User Manual. Use an RS-485 repeater to  
network several links of instruments.  
ꢀ
A maximum number of 31 Nexus 1250/1252 Meters may be connected to one repeater. A  
maximum number of 31 repeaters may be included on the same network.  
Maximum 31 Nexus 1250/1252 Meters, RS-485  
Maximum 31  
Repeaters  
REPEATER  
Nexus  
Nexus  
Nexus  
Nexus  
Nexus  
Maximum 31 Nexus Meters, RS-485  
REPEATER  
Nexus  
Nexus  
Nexus  
Nexus  
Nexus  
RS-485/232  
Converter  
Figure 5.15: Networking Groups of Nexus Meters  
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5.16: Remote Communication Overview  
ꢀ
Use modems (dedicated or dial-up) when devices are at great distances. EIG recommends using  
RS-485 wiring with a Modem Manager. See section 5.13.  
Remote Connection—RS-232  
PC at office  
Local  
Modem  
PSTN (Public  
Switched  
Remote  
Modem  
Nexus 1250/1252  
Meter  
Telephone  
Network)  
RS-232  
NULL Modem Adapter or Null  
Cable Required  
Remote Connection—RS-485  
PC at office  
Originate  
Modem  
Telephone Line  
Remote  
Modem  
Nexus 1250/1252  
Meter  
RS-  
NULL Modem Adapter  
(Required if 232/485 Converter does not support  
RS-232 to RS-485  
Converter  
DTE/DCE reconfiguration)  
(Modem Manager  
Recommended)  
Figure 5.16: Remote Connections—RS-232/RS-485  
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ꢀ
Use RJ-11 Telephone Lines when devices are at great distances. Connections are simple, requiring  
no additional hardware.  
RS-485  
RJ-11  
Daisy Chain  
Originate Modem  
PC  
(or Internal to PC)  
Figure 5.17: Remote Connections with Internal Modem Option  
ꢀ
ꢀ
Standard Telephone wall to phone cabling can be used. This cabling is widely available in many  
lengths with RJ-11 plugs on each end.  
Plug one end into the Nexus 1250/1252 and the other end into the wall jack.  
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ꢀ
Or, use RJ-45 Network Connection when devices are at great distances. Connections are simple,  
requiring no additional hardware.  
RS-485  
MODBUS/RTU  
10/100BaseT  
or 10BaseT  
RJ-45  
MODBUS/TCP  
over Ethernet  
Daisy Chain  
Network  
Figure 5.18: Remote Connections with Internal Network Option  
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5.17: Remote Communication—RS-232  
ꢀ
EIG recommends using RS-485 wiring with a Modem Manager. See section 5.13.  
ꢀ
For RS-232 communication, use Port 1. Set the selector switch under the port to RS-232 (Fig. 5.3).  
ꢀ
Use an RS-232 serial extension cable connected to the 9-pin female serial port of the Nexus  
1250/1252 Meter’s Port 1. Program this port for Modbus ASCII. See the Communicator EXT User  
Manual for details.  
ꢀ
The link using RS-232 is capable for up to 50 feet (1219 meters).  
ꢀ
You must use a Null Modem or Null Cable between the Nexus Meter and the remote modem when  
using RS-232. A Null Modem enables two DCE devices to communicate. The figure below details  
how a null modem reconfigures the RS-232 pins. Note: Connecting the Nexus Meter to a modem  
via RS-485 protocol with EIG’s Modem Manager converter eliminates the need for a Null  
Modem; see section 5.13.  
ꢀ
The remote modem must be programmed for auto-answer and set at a fixed baud rate of 9600 with  
no Flow Control. See section 5.19 and the Communicator EXT User Manual for further details.  
Pins at Null Modem Male End  
20  
2
2
3
4
5
6
7
8
1
1
20  
3
8
7
4
5
6
Pins at Null Modem Female End  
Figure 5.19: Standard Null Modem Configuration  
5.18: Remote Communication—RS-485  
ꢀ
Use any Port on the Nexus 1250/1252. If you use Port 1, set the selector switch beneath the port to  
RS-485 (see Figure 5.3). The link using RS-485 is viable for up to 4000 feet (1219 meters).  
ꢀ
ꢀ
Use Communicator EXT software to set the port’s baud rate to 9600 and enable Modbus ASCII  
protocol. See the Communicator EXT User Manual.  
You must use an RS-485 to RS-232 converter and a NULL Modem. EIG recommends using its  
Modem Manager, a sophisticated RS-232/RS-485 converter that enables devices with different  
baud rates to communicate. It also eliminates the need for a NULL modem (see section 5.12), and  
automatically programs the modem to the proper configuration. Also, if the telephone lines are poor,  
Modem Manager acts as a line buffer, making the communication more reliable.  
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5.19: Programming Modems for Remote Communication  
When a modem speaks to most RS-485 or RS-232-based devices, it must be programmed for the  
communication to work. This task is often quite complicated because modems are quirky when talking  
to remote devices.  
If you are not using a Modem Manager device, you must set the following strings to communicate with  
the remote Nexus Meter(s). Consult your modem’s manual for the proper string settings or see section  
5.15 for a list of selected modem strings.  
ꢀ
Modem Connected to a Computer (the Originate Modem):  
•
•
•
•
Restore modem to factory settings. This erases all previously programmed settings.  
Set modem to display Result Codes. The computer will use the result codes.  
Set modem to Verbal Result Codes. The computer will use the verbal result codes.  
Set modem to use DTR Signal. This is necessary for the computer to ensure connection with the  
originate modem.  
•
•
Set modem to enable Flow Control. This is necessary to communicate with remote modem  
connected to the Nexus.  
Tell modem to write the new settings to activate profile. This places these settings into  
nonvolatile memory; the setting will take effect after the modem powers up.  
ꢀ
Modem Connected to the Nexus Meter (the Remote Modem):  
•
•
Restore modem to factory settings. This erases all previously programmed settings.  
Set modem to auto answer on N rings. This sets the remote modem to answer the call after N  
rings.  
•
•
•
•
Set modem to ignore DTR Signal. This is necessary for the Nexus to ensure connection with  
originate modem.  
Set modem to disable Flow Control. Nexus RS-232 communication does not support this  
feature.  
Tell modem to write the new settings to activate profile. This places these settings into  
nonvolatile memory; the setting will take effect after the modem powers up.  
When programming the remote modem with a terminal program, make sure the baud rate of the  
terminal program matches the Nexus Meter’s baud rate.  
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5.20: Selected Modem Strings  
Modem  
String/Setting  
Cardinal modem:  
AT&FE0F8&K0N0S37=9  
Zoom/Faxmodem VFX V.32BIS(14.4K): AT&F0&K0S0=1&W0&Y0  
Zoom/Faxmodem 56Kx Dual Mode:  
USRobotics Sportster 33.6 Faxmodem:  
DIP switch setting:  
USRobotics Sportster 56K Faxmodem:  
DIP switch setting:  
AT&F0&K0&C0S0=1&W0&Y0  
AT&F0&N6&W0Y0 (for 9600 baud)  
Up Up Down Down Up Up Up Down  
AT&F0&W0Y0  
Up Up Down Down Up Up Up Down  
5.21: High Speed Inputs Connection  
ꢀ
The Nexus High Speed Inputs can be used in many ways:  
Attach the KYZ HS Outputs from other meters for totalizing.  
Attach relaying contacts for breaker status or initiated logging.  
ꢀ
ꢀ
Refer to the Communicator EXT User Manual for information on programming the functionality of  
these versatile inputs.  
The High Speed Inputs can be used with either dry or wet field contacts. For WET contacts, the  
common rides on a unit-generated 15V DC. No user programming is necessary to use either wet or  
dry field contacts.  
7
8
6
5
3
1
C
4
+
Optional 150V Max for wet contacts  
Figure 5.20: High Speed Inputs Connection  
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5.22: Five Modes of Time Synchronization  
ꢀ
The Nexus meter offers up to five modes of Time Synchronization, depending on options selected at  
the time of ordering.  
1. Internal Crystal: The Default Time Constant is an Internal Crystal. The crystal is accurate to  
approximately 1 minute per month.  
2. Line Frequency: The meter ignores the internal crystal and counts frequency to synchronize the  
clock. This feature is highly accurate in the presence of reliable system frequency. If power is  
lost, the unit automatically switches to the internal crystal.  
3. Modbus Commands Time Synchronization: The meter uses Serial Modbus-Based Commands  
to change the date and time of the clock. The meter relies upon the Internal Crystal between  
synchronization intervals. This mode is used in conjunction with MV90.  
4. DNP Line Synchronization: The meter uses DNP Protocol Commands to change the date and  
time of the clock. The meter relies upon the Internal Crystal between synchronization intervals.  
5. IRIG-B: The meter uses a Signal Generating Device connected to the GPS Satellite System to  
synchronize Nexus Time. This mode is accurate to within one millisecond. This mode is  
detailed in section 5.23.  
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5.23: IRIG-B Connections  
ꢀ
IRIG-B is a standard time code format that synchronizes event timestamping to within 1 millisecond.  
An IRIG-B signal-generating device connected to the GPS satellite system will synchronize Nexus  
1250/1252 Meters located at different geographic locations. Nexus utilizes an UNMODULATED  
signal from a satelite-controlled clock (such as Arbiter 1093B). For details on installation, refer to  
the User’s Manual for the satellite-controlled clock in use. Below are installation steps and tips that  
will help you.  
ꢀ
Connect the (+) terminal of the Nexus Meter to the (+) terminal of the signal generating device;  
connect the (-) terminal of the Nexus Meter to the (-) terminal of the signal generating device.  
Nexus IRIG-B Port  
IRIG-B Time  
+
-
+
-
Signal  
Generating  
Device  
Figure 5.21: IRIG-B Connection  
ꢀ
Installation:  
1. Set Time Settings for the meter being installed. From Communicator EXT, Device Profile,  
Click Time Settings. Set the Time Zone and Daylight Savings (Select AutoDST or Enable and  
set dates). Click Update Device Profile to save the new settings. (See the Communicator EXT  
User’s Manual for details.)  
2. Before connection, check that the date on the meter clock is correct (or, within 2 MONTHS of  
the actual date). This provides the right year for the clock (GPS does not supply the YEAR).  
3. Connect the (+) terminal of the Meter to the (+) terminal of the signal generating device;  
Connect the (-) terminal of the Meter to the (-) terminal of the signal generating device.  
ꢀ
Troubleshooting Tip: The most common source of problems is a reversal of the two wires. Try  
reversing the wires.  
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Chapter 6  
Using the Nexus External Displays  
6.1: Overview  
Q
Electro Industries offers four external displays for use with the Nexus 1250/1252. The P40N, P41N  
and P43N are LED displays that provide easy-to-use access to the information stored in the Nexus  
1250/1252. The P60N is our Touch Screen Display, which provides easy access to Nexus 1250/1252  
readings and information combined with a graphical touch screen presentation.  
Q
Plug one of the Nexus External Displays into Port 3 or 4 on the Nexus Meter, using the cable  
supplied. The Displays operate at 9600 baud; Port 3 is factory-set to 9600 baud (see Chapter 5 for  
communication details). To use the Displays on another port, configure that port to operate at 9600  
baud, using the Communicator EXT Software; see the Communicator EXT User Manual.  
6.2: Nexus P40N, P41N and P43N LED External Displays  
Q
The Nexus P40N LED External Display can be used alone or it can serve as the Master for this  
grouping of displays. The P40N prepares the data for the Slave displays, the P41N and the P43N.  
Once a second, it sends a request to the Nexus meter. All necessary data for the Slave displays is  
returned to the Master display upon this request and the Master sends the data to the Slaves in the  
proper format.  
Q
The Nexus P41N and P43N Slave displays listen to the Master and display and update values on the  
screen when they receive proper data. These displays have no keypads. Data can only be received;  
it cannot be changed. If there is no data for more than 5 seconds, “Communication Lost” will appear  
on the bottom of the screen. The following data is displayed when received:  
•
•
Amp Display (P41N): Amp A, Amp B, Amp C  
Power Display (P43N): Watt, VAR, PF  
LED Display  
Left/Right Arrows  
Mode Button  
Up/Down Arrows  
Figure 6.1: Nexus P40N LED External Display  
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6.2.1: Connect Multiple Displays  
Q
One cable (housing two-wire RS-485 and two-wire power wires plus shield) is used to connect the  
displays. One port of the Nexus meter supports 12 VA. Each P40N, P41N or P43N requires 3.3 VA  
(maximum 3.8 VA). The Master Display (P40N) is the master in communication. The Amp, Power  
and Nexus devices are slaves in communication. Therefore, the Master Display (P40N) should be at  
the end of the daisy-chained units as shown in Figure 6.2 below. The Nexus port is set at 1.  
Protocol is Modbus RTU and Baud Rate is 9600.  
NEXUS UNIT  
P43N  
P41N  
P40N  
+V -V S B(-) A(+)  
+V -V S B(-) A(+)  
+V -V S B(-) A(+)  
+V -V S B(-) A(+)  
Figure 6.2: P40N Display Daisy Chain  
NOTE: The power lines in Figure 6.2  
are shown separate for clarity.  
All lines are actually in one cable.  
Q
Shown here are diagrams of the  
P41N and P43N Displays with  
example readings on each screen.  
Figure 6.3: P41N Display  
Figure 6.4: P43N Display  
6.2.2: Nexus P40N Modes  
Q
The Nexus P40N LED External Display has three modes:  
•
•
•
Dynamic Readings Mode (section 6.3 and 6.4)  
Nexus Information Mode (section 6.5 and 6.6)  
Display Features Mode (section 6.7 and 6.8)  
Q
Each Mode is divided into Groups. Most Groups are further broken down into Readings.  
•
•
•
Use the MODE button to scroll between Modes.  
Use the UP/DOWN arrows to scroll from Group to Group within each Mode.  
Use the LEFT/RIGHT arrows to scroll from Reading to Reading within each Group.  
Q
Use the Communicator EXT software to Flash Update the P40N External Display.  
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6.3: Dynamic Readings Mode  
Q
The External Display puts itself in the Dynamic Readings Mode upon power-up. Use the MODE  
button to access the Dynamic Readings from other Modes. Use the UP/DOWN arrows to navigate  
from Group to Group within this Mode. See section 6.4 for a navigational map of the Dynamic  
Readings Mode.  
Q
Group 1: Phase to Neutral Voltages (Use the LEFT/RIGHT arrows to access the following  
readings, in order.)  
•
•
•
•
•
•
Volts AN/BN/CN  
Maximum Volts AN/BN/CN  
Minimum Volts AN/BN/CN  
Volts AN/BN/CN %THD  
Volts AN/BN/CN Maximum %THD  
Volts AN/BN/CN Minimum %THD  
Q
Group 2: Phase to Phase Voltages (Use the LEFT/RIGHT arrows to access the following readings,  
in order.)  
•
•
•
Volts AB/BC/CA  
Maximum Volts AB/BC/CA  
Minimum Volts AB/BC/CA  
Q
Group 3: Current (Use the LEFT/RIGHT arrows to access the following readings, in order.)  
•
•
•
•
•
•
•
•
Current A/B/C  
Maximum Current  
Minimum Current  
Current %THD  
Current Maximum %THD  
Current Minimum %THD  
Current Calculated N/Measured N  
Maximum Current Calculated N/Measured N  
Q
Group 4: Watt/VAR (Use the LEFT/RIGHT arrows to access the following readings, in order.)  
•
•
•
•
•
kWatt/kVAR  
Maximum +kWatt/+kVAR/CoIn kVAR  
Maximum -kWatt/-kVAR/CoIn kVAR  
Block (Fixed) Window Average Maximum +kWatt/+kVAR/CoIn kVAR  
Predictive Rolling (Sliding) Window Maximum +kWatt/+kVAR/CoIn kVAR  
Q
Group 5:VA/PF/Frequency (Use the LEFT/RIGHT arrows to access the following readings, in  
order.)  
•
•
•
kVA/PF lag/Hz  
Maximum kVA/Hz  
Minimum kVA/Hz  
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•
•
•
•
•
•
•
•
Maximum Quadrant 1 Total PF  
Minimum Quadrant 1 Total PF  
Maximum Quadrant 2 Total PF  
Minimum Quadrant 2 Total PF  
Maximum Quadrant 3 Total PF  
Minimum Quadrant 3 Total PF  
Maximum Quadrant 4 Total PF  
Minimum Quadrant 4 Total PF  
Q
Q
Q
Group 6: Delivered Energy (Use the LEFT/RIGHT arrows to access the following readings, in  
order.)  
•
•
•
•
•
+kWatthr Quadrant 1+Quadrant 4 (Primary)  
+kVAhr Quadrant 1 (Primary)  
+kVARhr Quadrant 1 (Primary)  
+kVAhr Quadrant 4 (Primary)  
-kVARhr Quadrant 4 (Primary)  
Group 7: Received Energy (Use the LEFT/RIGHT arrows to access the following readings, in  
order.)  
•
•
•
•
•
-kWatthr Quadrant 2+Quadrant 3 (Primary)  
+kVAhr Quadrant 2 (Primary)  
+kVARhr Quadrant 2 (Primary)  
+kVAhr Quadrant 3 (Primary)  
-kVARhr Quadrant 3 (Primary)  
Group 8: Accumulations (Use the LEFT/RIGHT arrows to access the following readings, in order.)  
•
•
•
•
•
•
kI2t A  
kI2t B  
kI2t C  
kV2t A  
kV2t B  
kV2t C  
Q
Group 9: Phase Angles (Use the LEFT/RIGHT arrows to access the following readings, in order.)  
•
•
•
•
Phase Angle Van/bn/cn  
Phase Angle Ia/b/c  
Phase Angle Vab/bc/ca  
Phase Sequence  
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6.4: Navigational Map of Dynamic Readings Mode  
Q
Use LEFT/RIGHT arrow keys to navigate Readings  
Q
Use UP/DOWN arrows to scroll between groups.  
G
Max %THD  
Volts  
AN,BN,CN  
Min %THD  
Volts  
AN,BN,CN  
Return to  
First  
Reading  
r
o
u
p
s
1 Second Volts  
AN,BN,CN  
Maximum Volts  
AN,BN,CN  
Minimum Volts  
AN,BN,CN  
%THD Volts  
AN,BN,CN  
Return to  
First  
Reading  
Minimum Volts  
AB,BC,CA  
1 Second Volts  
AB,BC,CA  
Maximum Volts  
AB,BC,CA  
Return to  
First  
Reading  
1 Second  
IA,IB,IC  
Minimum  
IA,IB,IC  
%THD  
IA,IB,IC  
Max %THD  
IA,IB,IC  
Maximum  
IA,IB,IC  
Min %THD  
IA,IB,IC  
1 Second  
INc,INm  
+Max kWatt,  
+kVAR,CoIn  
kVAR  
-Max kWatt,  
-kVAR,CoIn  
kVAR  
Block WinAvg Max  
+kWatt,  
+kVAR,CoIn kVAR  
Pred Rol Win Avg  
+kWatt,  
+kVAR,CoIn kVAR  
Return to  
First  
Reading  
1 Second  
kWatt, kVAR  
1 Second  
kVA, PF  
lag,  
Return to  
First  
Reading  
Max  
kVA,  
Freq  
Min  
kVA,  
Freq  
Min Q3,  
Total PF  
Max Q1, Min Q1, Max Q2, Min Q2, Max Q3,  
Total PF Total PF Total PF Total PF Total PF  
Min Q4, Min Q4,  
Total PF Total PF  
Frequency  
Positive  
kVARhr  
Q1  
Positive  
kVAhr  
Q4  
Negative  
kVARhr  
Q4  
Return to  
First  
Reading  
Positive  
kWatthour  
Q1+Q4  
Positive  
kVAhr  
Q1  
Negative  
kVARhr  
Q3  
Positive  
kVARhr  
Q2  
Positive  
kVAhr  
Q2  
Return to  
First  
Reading  
Negative  
kWatthr  
Q2+Q3  
Positive  
kVAhr  
Q3  
Return to  
First  
Reading  
kI2t A  
kI2t B  
kI2t C  
kV2t A  
kV2t B  
kV2t C  
Phase Angles V  
AN,BN,CN  
Phase Angles I  
A,B,C  
Phase Angles V  
AB,BC,CA  
Return to First  
Reading  
Phase  
Sequence  
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6.5: Nexus Information Mode  
Q
Use the MODE button to access the Nexus Information Mode from other Modes. Use the  
UP/DOWN arrows to navigate from Group to Group within this Mode. See section 6.6 for a  
navigational map of the Nexus Information Mode.  
Q
Group 1: Device Time  
•
Meter Time  
Q
Group 2: Communication Settings (Use the LEFT/RIGHT arrows to access the following readings,  
in order.)  
•
•
•
•
Communication Settings Port 1: Baud/Addr/Protocol  
Communication Settings Port 2: Baud/Addr/Protocol  
Communication Settings Port 3: Baud/Addr/Protocol  
Communication Settings Port 4: Baud/Addr/Protocol  
Q
Q
Group 3: PT, CT Ratios (Use the LEFT/RIGHT arrows to access the following readings, in order.)  
•
•
PT Ratio  
CT Ratio  
Group 4: External Display Units  
•
•
Primary/Secondary  
Select either Primary or Secondary units for the External Display using the Communicator EXT  
software (see the Energy Manager User Manual).When Primary is selected, the Display shows  
all readings in Primary units based on the user programmed PT and CT Ratios. When Secondary  
is selected, the Display shows all readings in Secondary units.  
Q
Group 5: Firmware Versions and Serial Numbers (Use the LEFT/RIGHT arrows to access the  
following readings, in order.)  
•
•
•
Run Time External Display/Run Time DSP/RunTime Comm  
Boot External Display/Boot DSP/Boot Comm  
Serial Number External Display; Serial Number Nexus Monitor  
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6.6: Navigational Map of Nexus Information Mode  
Q
Use UP/DOWN arrows to scroll between groups.  
Q
Use LEFT/RIGHT arrows to scroll between readings.  
Readings  
G
r
Meter Time  
o
u
p
s
Comm  
Settings  
Return  
To  
First Reading  
Comm  
Settings  
Port 2  
Comm  
Settings  
Port 3  
Comm  
Settings  
Port 4  
Port 1  
Return  
To  
PT Ratio  
CT Ratio  
First Reading  
Display  
Primary/Secondary  
Return  
To  
First  
Serial #  
Display, Serial  
# Monitor  
Run-time  
Display,  
DSP, Comm  
Boot  
Display,  
DSP, Comm  
Reading  
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6.7: Display Features Mode  
Q
Use the MODE button to access the Display Features Mode from other Modes. Use the UP/DOWN  
arrows to navigate from Group to Group within this Mode. See section 6.8 for a navigational map of  
the Display Features mode.  
Q
Group 1: Reset Max/Min  
•
Note: If the password protection feature has been enabled with the Communicator EXT  
software, you will need to enter a password to reset the max/min readings. To do this, first press  
the Enter button. Then enter the password, one character at a time, by pressing on the UP or  
DOWN arrows. Each password character begins as an “A”. Press the UP arrow to increment the  
character from “A–Z” and then from “0–9”. Press the DOWN arrow to decrement the character  
from “A” to “9–0” and then from “Z–A”. Press SET to enter each character the password. When  
the entire password is shown on the Display screen, press ENTER. If the password is correct you  
may then press Enter again to Reset the Energy readings.  
•
Press the Enter button to reset the Max and Min values.  
Q
Group 2: Reset Energy  
•
Note: If the password protection feature has been enabled with the Communicator EXT  
software, you will need to enter a password to reset the energy. To do this, first press the Enter  
button. Then enter the password, one character at a time, by pressing on the UP or DOWN  
arrows. Each password character begins as an “A”. Press the UP arrow to increment the  
character from “A–Z” and then from “0–9”. Press the DOWN arrow to decrement the character  
from “A” to “9–0” and then from “Z–A”. Press SET to enter each character the password. When  
the entire password is shown on the Display screen, press ENTER. If the password is correct you  
may then press Enter again to Reset the Energy readings.  
•
Press Enter button to reset the Max and Min values.  
Q
Q
Q
Q
Q
Group 3: Display Baud Rate/Address  
Group 4: Display Communication Protocol  
Group 5: EIG Use Only  
Group 6: EIG Use Only  
Group 7: Lamp Test  
•
Press Enter to conduct an LED test.  
Q
Group 8: Display Scroll ON/OFF  
•
Press Enter to turn the scroll feature on or off. When the scroll feature is on, the P40N External  
Display will scroll through the first reading of each group in the Dynamic Readings Mode. If a  
button is pressed during the scroll, scrolling pauses for one minute.  
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6.8: Navigational Map of Display Features Mode  
Q
Use UP/DOWN arrows to scroll between groups.  
G
r
Reset Max/Min  
o
u
p
s
Reset Energy  
Baud  
Rate/Address  
Communication  
Protocol  
EIG Use Only  
EIG Use Only  
Lamp Test  
Display Scroll  
On/Off  
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6.9: Nexus P60N Touch Screen External Display  
Q
The P60N Touch Screen External Display is ready to use upon power-up. Touching the “buttons” at  
the top of the screen will take you to the Groups of Readings listed below. With the “buttons” at  
the bottom of the screen, you can use the touch screen to review Limits and review and/or change  
Settings on the Display and the Nexus Meter. Also, you can Reset Max/Min and Demand, Hour, I2T  
and V2T Counters, All Logs and TOU for Current Session and Month using the Reset Button.  
Q
All screens have a Main button that returns you to the Main screen below. All screens also have a  
Next button that will take you to the next group of readings. Some of the screens have additional  
navigation buttons to take you to complimentary readings. See section 6.10 for a navigational map.  
General Page  
Groups of Readings  
Reset Button  
View Limits  
View / Change Settings  
Figure 6.2: Nexus P60N Touch Screen External Display (Main Screen)  
Q
GENERAL PAGE: Overview of Real Time  
Readings  
•
•
•
•
•
•
•
Volts AN/BN/CN/AB/BC/CA  
Amps A/B/C  
Watts  
VARS  
VA  
FREQ  
PF  
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Q
VOLTS: Voltage Readings Details  
•
•
•
Real Time Volts AN/BN/CN/AB/BC/CA  
Maximum Volts AN/BN/CN/AB/BC/CA  
Minimum Volts AN/BN/CN/AB/BC/CA  
Touch PH-N or PH-PH to view details of  
Phase-to-Neutral or Phase-to-Phase Readings.  
Q
Q
Q
VOLTS: Voltage Readings PH-N  
•
Volts AN/BN/CN  
Touch BACK to return to the Volts main screen.  
VOLTS: Voltage Readings PH-PH  
•
Volts AB/BC/CA  
Touch BACK to return to the Volts main screen.  
AMPS: Current Readings Details  
•
•
•
•
•
Real Time Current A/B/C  
Maximum Current A/B/C  
Minimum Current A/B/C  
Current Calculated N/Measured N  
Maximum Current Calculated N/  
Measured N  
Touch A-B-C to view Currents Detail.  
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Q
AMPS: Current Readings A-B-C  
Real Time Current A/B/C  
•
Touch BACK to view the Amps main screen.  
Q
REAL TIME POWER: Real Time Power  
Readings Details  
•
•
•
Instant Watt/VAR/VA/PF  
Average Watt/VAR/VA/PF  
Predicted Watt/VAR/VA  
Touch the DEMAND button to go to the Demand  
Power screen (shown below)  
Q
DEMAND POWER: Demand Power Readings  
Details  
•
•
•
Thermal Window Average Maximum  
+kWatt/+kVAR/CoIn kVAR  
Block (Fixed) Window Average Maximum  
+kWatt/+kVAR/CoIn kVAR  
Predictive Rolling (Sliding) Window Maximum  
+kWatt/+kVAR/CoIn kVAR  
Touch R/T button to view Real Time Power screen.  
Q
ENERGY: Accumulated Energy Information  
•
•
•
•
•
•
•
-Watthr Quadrant 2+Quadrant 3 (Primary)  
+VAhr Quadrant 2 (Primary)  
+VARhr Quadrant 2 (Primary)  
+VAhr Quadrant 3 (Primary)  
-VARhr Quadrant 3 (Primary)  
+Watthr Quadrant 1+Quadrant 4 (Primary)  
+VAhr for all Quadrants (Primary)  
Touch TOU button to view TOU Register  
Accumulations screen.  
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Q
TOU: Accumulations  
•
•
•
•
•
•
•
•
-Watthr Quadrant 2+Quadrant 3 (Primary)  
+VAhr Quadrant 2 (Primary)  
+VARhr Quadrant 2 (Primary)  
+VAhr Quadrant 3 (Primary)  
-VARhr Quadrant 3 (Primary)  
+Watthr Quadrant 1+Quadrant 4 (Primary)  
+VAhr Quadrants 1 & 4 (Primary)  
-VARhr Quadrant 4 (Primary)  
Touch DEMAND to view Register Demand screen.  
Touch Next Reg to scroll Registers 1 - 8 and Totals.  
Touch Next Group to scroll Prior Season, Prior  
Month, Current Season, Current Month.  
Q
TOU: Register Demand  
•
Block (Fixed) Window +kWatth, +kVARhr,  
-kWatth, -kVARh, Coin +kVARh,  
Coin -kVARh  
Touch ACCUM to view TOU Accumulations.  
Touch Next Reg to scroll Registers 1 - 8 and Totals.  
Touch Next Group to scroll Prior Season, Prior  
Month, Current Season, Current Month.  
Q
FLICKER - INSTANTANEOUS:  
•
•
•
•
•
Time Start/Reset, Stop, Current, Next PST, PLT  
Status (Active or Stopped)  
Frequency  
Base Voltage  
Frequency  
Touch SHORT TERM or LONG TERM to view  
other Flicker screens.  
START or STOP will appear, depending on Status.  
Q
FLICKER - SHORT TERM:  
•
•
•
Volts A/B/C  
Max Volts A/B/C  
Min Volts A/B/C  
Touch INST or LONG TERM to view screens.  
START or STOP will appear, depending on Status.  
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Q
FLICKER - LONG TERM:  
•
•
•
Volts A/B/C  
Max Volts A/B/C  
Min Volts A/B/C  
Touch INST or LONG TERM to view other  
Flicker screens.  
START or STOP will appear, depending on Status.  
Q
LIMITS: Limit Status  
Current Limits Settings for Nexus Meters, ID 1 - 32.  
For each ID number, the Type of Reading, Value,  
Status (In or Out of Limit) and Setting is shown.  
The first screen displays the settings for Meters ID  
1 to 8.  
Touch NEXT GROUP to scroll to the next screen,  
which displays the settings for Meters ID  
9 to 16. Touch NEXT GROUP again to view  
settings for Meters ID 17 to 24 and 25 to 32.  
Q
PHASORS: Phasor Analysis  
Phase Angles for Form shown at top of the screen.  
•
•
•
•
Phase  
Phase Angle Van/bn/cn  
Phase Angle Ia/b/c  
Phase Angle Vab/bc/ca  
Q
WAVEFORM: Real Time Graph.  
•
•
•
Channel Va/b/c  
Channel Ia/b/c  
% THD, KFactor, Frequency for  
selected channel  
Touch CHANNEL button to view scroll through  
channels.  
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Q
SPECTRUM: Harmonic Spectrum Analysis.  
Select a Channel by touching the CHANNEL  
button. Graphs and readings appear for the  
selected channel.  
Zoom In or Out for detail by touching IN or OUT.  
Q
REAL TIME TRENDING ANALYSIS:  
Select Channel by touching the CHANNEL  
button. The Channel Selector screen (shown  
below) appears.  
Select a Channel and touch OK to select channel  
and return to this screen. Trending for the Selected  
Channel will begin on this screen.  
To see a Detail of logs for the Selected Channel,  
touch the DETAIL Button. A Table of Logs for the  
Selected Channel appears (Volts AN shown below).  
Touch PREVIOUS LOGS to view other logs.  
Q
REAL TIME TRENDING CHANNEL  
SELECTOR:  
Select Channel by touching a CHANNEL Button.  
The Active Channel appears at the lower right.  
Data from the previously Active Channel will  
be lost if the Channel is changed.  
The Time Interval for Trending appears at the  
bottom of the screen. To increase the Interval,  
touch the UP button. To decrease the Interval,  
touch DN (Down).  
Touch OK to return to Trending Analysis screen.  
Q
REAL TIME TRENDING DETAIL  
A Table of Logs for the Selected Channel  
(Volts AN shown here).  
Touch BACK to return to the Trending Analysis  
screen.  
Touch PREVIOUS LOGS to view other logs.  
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Q
LOG STATUS: Logging Statistics  
An Overview of the Logs for the Primary  
Meter.  
The Number of Records and Memory Used  
are listed for each log.  
Q
RESET: Meter Reset Commands.  
WARNING! RESETS cause data to be lost.  
Touch the window for the Reset you want to perform.  
Don’t Reset changes to Reset.  
Touch RESET NOW button. OK will appear.  
Touch OK to refresh screen (go back to original  
screen).  
•
•
•
•
Max/Min and Demand.  
Hour, I2T and V2T Counters.  
All Logs.  
TOU for Current Session and Month.  
Q
Q
SETTINGS:  
LCD SCREEN SETTINGS:  
Contrast. Touch Up/Down buttons to  
increase/decrease settings.  
Number 37 is optimum setting.  
Backlight Off Delay (number of seconds  
after use that backlight turns off).  
Touch Up/Down buttons to  
increase/decrease settings.  
Q
NEXUS LINK SETTING:  
Nexus Address (000 - 255).  
Touch Up/Down buttons to  
increase/decrease settings.  
Protocol (selected).  
Baud (selected).  
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Q
Q
Q
NEXUS PORT SETTINGS:  
Port 1 (Baud and Protocol selected).  
Port 2 (Baud and Protocol selected).  
Port 3 (Baud and Protocol selected).  
Port 4 (Baud and Protocol selected).  
NEXUS STATUS:  
Device Type: Nexus 1252  
Serial Number (10 digit number)  
Comm State: Healthy or Unhealthy  
Nv Ram: 4 MB  
DSP State: Healthy or Unhealthy  
Protection: Password Enabled or Disabled  
On Time: Current Date and Time  
FIRMWARE VERSIONS:  
Nexus 1252  
Boot: 601  
Run-time: 606  
DSP Boot: 600  
DSP Run-time: 604  
LCD Display: AAD  
This screen displays the current firmware  
version for the Nexus and the display.  
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6.10: Navigational Map for P60N Touch Screen External Display  
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Chapter 7  
Transformer Loss Compensation  
7.1: Introduction  
Q
The Edison Electric Institute’s Handbook for Electricity Metering, Ninth Edition defines Loss  
Compensation as:  
A means for correcting the reading of a meter when the metering point and point of service are  
physically separated, resulting in measurable losses including I2R losses in conductors and  
transformers and iron-core losses. These losses may be added to or subtracted from the meter  
registration.  
Q
Loss compensation may be used in any instance where the physical location of the meter does not  
match the electrical location where change of ownership occurs. Most often this appears when  
meters are connected on the low voltage side of power transformers when the actual ownership  
change occurs on the high side of the transformer. This condition is shown pictorially in Figure 7.1.  
Ownership Change  
M
Figure 7.1: Low Voltage Metering Installation Requiring Loss Compensation  
Q
Q
It is generally less expensive to install metering equipment on the low voltage side of a transformer  
and in some conditions other limitations may also impose the requirement of low-side metering even  
though the actual ownership change occurs on the high-voltage side.  
The need for loss compensated metering may also exist when the ownership changes several miles  
along a transmission line where it is simply impractical to install metering equipment. Ownership  
may change at the midway point of a transmission line where there are no substation facilities. In  
this case, power metering must again be compensated. This condition is shown in Figure 7.2.  
M
Point of Ownership  
Change  
Figure 7.2: Joint Ownership Line Metering Requiring Loss Compensation  
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Q
Q
A single meter cannot measure the losses in a transformer or transmission line directly. It can  
however, include computational corrections to calculate the losses and add or subtract those losses to  
the power flow measured at the meter location. This is the method used for loss compensation in the  
Nexus meter.  
The computational corrections used for transformer and transmission line loss compensation are  
similar. Generically, no-load losses and full-load losses are evaluated and a correction factor for each  
loss level is calculated. However, the calculation of the correction factors that must be programmed  
into the meter differ for the two different applications. For this reason, the two methodologies will be  
treated separately in this chapter.  
Q
In the Nexus meter, Loss Compensation is a technique that computationally accounts for active and  
reactive power losses. The meter calculations are based on the formulas below. These equations  
describe the amount of active (Watts) and reactive (VARs) power lost due to both iron and copper  
effects (reflected to the secondary of the instrument transformers).  
Total Secondary Watt Loss =  
(((Measured Voltage/Cal point Voltage)2 x %LWFE) + ((Measured Current/Cal Point Current)2  
x %LWCU)) x Full-scale Secondary VA  
Total Secondary VAR Loss =  
(((Measured Voltage/Cal point Voltage)4 x %LVFE) + ((Measured Current/Cal Point Current)2  
x %LVCU)) x Full-scale Secondary VA  
Q
Q
The Values for %LWFE, %LWCU, %LVFE, %LVCU are derived from the transformer and meter  
information, as demonstrated in following sections.  
The calculated loss compensation values are added to or subtracted from the measured Watts and  
VARs. The selection of adding or subtracting losses is made through the meter profile when  
programming the meter. The meter uses the combination of the add/subtract setting and the  
directional definition of power flow (also in the profile) to determine how to handle the losses.  
Losses will be "added to" or "subtracted from" (depending on whether add or subtract is selected)  
the Received Power flow. For example, if losses are set to "Add to" and received power equals 2000  
kW and losses are equal to 20kW then the total metered value with loss compensation would be  
2020 kW; for these same settings if the meter measured 2000 kW of delivered power the total  
metered value with loss compensation would be 1980 kW.  
Q
Q
Since transformer loss compensation is the more common loss compensation method, the meter has  
been designed for this application. Line loss compensation is calculated in the meter using the same  
terms but the percent values are calculated by a different methodology as described in a subsequent  
section below.  
Nexus 1250/1252 Transformer Loss Compensation:  
•
Performs calculations on each phase of the meter for every measurement taken. Unbalanced  
loads are accurately handled.  
•
Calculates numerically, eliminating the environmental affects that cause inaccuracies in  
electromechanical compensators.  
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•
•
•
Performs Bidirectional Loss Compensation.  
Requires no additional wiring; the compensation occurs internally.  
Imposes no additional electrical burden when performing Loss Compensation.  
Q
Loss Compensation is applied to 1 second per phase Watt/VAR readings and, because of that, affects  
all subsequent readings based on 1 second per phase Watt/VAR readings. This method results in loss  
compensation be applied to the following quantities:  
•
•
Total Power.  
Demands, per phase and Total (Thermal, Block (Fixed) Window, Rolling (Sliding) Window and  
Predictive Window).  
•
•
•
Maximum and Minimum Demands.  
Energy Accumulations.  
KYZ Output of Energy Accumulations.  
NOTE: Loss Compensation is disabled when the meter is placed in Test Mode.  
7.2: Nexus 1250/1252 Transformer Loss Compensation  
Q
The Nexus meter provides compensation for active and reactive power quantities by performing the  
numerical calculations using factors derived by clicking the TLC Calculator button on the  
Transformer Loss screen of the Device Profile or by manually figuring values in section 7.2.1,  
Calculating Transformer Loss Compensation Percentages (Work Sheet). Enter the derived values in  
the Device Profile screen of the Nexus Communicator software (values will automatically be entered  
from the TLC Calculator button).  
Q
The Nexus Communicator software allows you to enable Transformer Loss Compensation for Losses  
due to Copper and Iron, individually or simultaneously. Losses can either be added to or subtracted  
from measured readings.  
Q
Loss compensation values must be calculated based on the meter installation. As a result transformer  
loss values must be normalized to the meter by converting the base voltage and current and taking  
into account the number of elements used in the metering installation. For three element meters, the  
installation must be normalized to the phase-to-neutral voltage and the phase current; in two element  
meters the installation must be normalized to the phase-to-phase voltage and the phase current. This  
process is described in the following sections.  
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7.2.1: Loss Compensation in Three Element Installations  
Q
Loss compensation is based on the loss and impedance values provided on the transformer  
manufacturer’s test report. A typical test report will include at least the following information:  
•
•
•
•
•
•
•
•
Manufacturer  
Unit Serial Number  
Transformer MVA Rating (Self-Cooled)  
Test Voltage  
No Load Loss Watts  
Load Loss Watts (or Full Load Loss Watts)  
% Exciting Current @ 100% voltage  
% Impedance  
Q
The transformer MVA rating is generally the lowest MVA rating (the self-cooled or OA rating) of the  
transformer winding. The test voltage is generally the nominal voltage of the secondary or low  
voltage winding. For three phase transformers these values will typically be the three-phase rating  
and the phase-to-phase voltage. All of the test measurements are based on these two numbers. Part of  
the process of calculating the loss compensation percentages is converting the transformer loss  
values based on the transformer ratings to the base used by the meter.  
Q
Correct calculation of loss compensation also requires knowledge of the meter installation. In order  
to calculate the loss compensation settings you will need the following information regarding the  
meter and the installation:  
•
•
•
•
•
Number of meter elements  
Potential Transformer Ratio (PTR)  
Current Transformer Ratio (CTR)  
Meter Base Voltage  
Meter Base Current  
Q
This section is limited to application of Nexus meters to three-element metering installations. As a  
result, we know that:  
•
•
•
Number of metering elements = 3  
Meter Base Voltage = 120 Volts  
Meter Base Current = 5 amps  
Q
The loss compensation values can be calculated by clicking the TLC Calculator button on the  
Transformer Loss screen of the Nexus Device Profile (MS Excel Spreadsheet) or by completing the  
worksheet “Three Element Loss Compensation Worksheet” below. In order to activate the Excel  
Spreadsheet, you must have MS Excel installed on your computer.  
NOTE: A copy of the Excel Spreadsheet with Example Numbers can be found in Appendix A of this  
manual.  
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7.2.1.1: Three Element Loss Compensation Worksheet  
Company  
Date  
Station Name  
Trf Bank No.  
Trf Serial No.  
Trf Manf  
Calculation by  
Q
Transformer Data (from Transformer Manufacturer’s Test Sheet)  
Winding  
HV - High  
Voltage  
MVA  
Connection  
∆ - Y  
Xv - Low  
∆ - Y  
YV - Tertiary  
∆ - Y  
Watts Loss  
Value  
3-Phase  
1-Phase  
1-Phase kW  
No-Load Loss  
Load Loss  
Enter 3-Phase or 1-Phase values. If 3-Phase values are entered, calculate 1-Phase values by dividing  
3-Phase values by three. Convert 1-Phase Loss Watts to 1-Phase kW by dividing 1-Phase Loss Watts by  
1000.  
Value  
3-Phase MVA  
1-Phase MVA  
1-Phase kVA  
Self-Cooled Rating  
Enter 3-Phase or 1-Phase values. If 3-Phase values are entered, calculate 1-Phase values by dividing  
3-Phase values by three. Convert 1-Phase Self-Cooled MVA to 1-Phase kVA by multiplying by 1000.  
% Exciting Current  
% Impedance  
Value  
Phase-to-Phase  
Phase-to-Neutral  
Test Voltage (volts)  
Full Load Current (Amps)  
Test Voltage is generally Phase-to-Phase for three-phase transformers. Calculate Phase-to-Neutral  
Voltage by dividing Phase-to-Phase Voltage by √3. Calculate Full Load Current by dividing the (1-Phase  
kW Self-Cooled Rating) by the (Phase-to-Neutral Voltage) and multiplying by 1000.  
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Q
Meter/Installation Data  
Instrument Transformers  
Potential Transformer  
Current Transformer  
Numerator  
Denominator  
Multiplier  
Power Multiplier [(PT Multiplier) times (CT Multiplier)]  
Enter the Numerator and Denominator for each instrument transformer. For example, a PT with a ratio  
of 7200/120 has a numerator or 7200, a denominator or 120 and a multiplier of 60 ( 7200/120 = 60/1).  
Meter Secondary Voltage (volts)  
Meter Secondary Current (amps)  
120  
5
Q
Base Conversion Factors  
Quantity  
Voltage  
Current  
Transformer  
Multiplier  
Trf IT Sec  
Meter Base  
Meter/Trf  
120  
5
For Transformer Voltage, enter the Phase-to-Neutral value of Test Voltage previously calculated. For  
Transformer Current, enter the Full-Load Current previously calculated. For Multipliers, enter the PT  
and CT multipliers previously calculated.  
TrfIT Secondary is the Base Value of Voltage and Current at the Instrument Transformer Secondary of  
the Power Transformer. These numbers are obtained by dividing the Transformer Voltage and Current  
by their respective Multipliers. The Meter/Trf values for Voltage and Current are obtained by dividing  
the Meter Base values by the TrfIT Secondary values.  
Q
Load Loss at Transformer  
No-Load Loss Watts (kW) = 1-Phase kW No-Load Loss = ______________  
No-Load Loss VA (kVA)  
= (%Exciting Current) * (1-Phase kVA Self-Cooled Rating) / 100  
= (______________) * (________________) / 100  
= _______________ kVA  
No-Load Loss VAR (kVAR)  
= SQRT((No-Load Loss kVA)2 - (No-Load Loss kW)2)  
= SQRT((_________________)2 - (________________)2)  
= SQRT((__________________) - (_________________))  
= SQRT (_________________)  
= ____________________  
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Full-Load Loss Watts (kW) = 1-Phase Kw Load Loss = ______________  
Full-Load Loss VA (kVA) = (%Impedance) * (1-Phase kVA Self-Cooled Rating) / 100  
= (______________) * (________________) / 100  
= _______________ kVA  
Full-Load Loss VAR (kVAR) = SQRT((Full-Load Loss kVA)2 - (Full-Load Loss kW)2)  
= SQRT((_________________)2 - (________________)2)  
= SQRT((__________________) - (_________________))  
= SQRT (_________________)  
= _________________  
Q
Normalize Losses to Meter Base  
Value at Trf  
Base  
M/T  
Factor  
M/T Factor  
Value  
M/T Factor w/  
Exp  
Value at  
Meter Base  
Quantity  
Exp  
∧
No-Load Loss kW  
No-Load Loss kVAR  
Load Loss kW  
V
V
I
2
∧
4
∧
2
∧
Load Loss kVAR  
I
2
Enter Value at Transformer Base for each quantity from calculations above. Enter Meter/Trf Factor  
value from Base Conversion Factor calculations above. Calculate M/T Factor with Exponent by raising  
the M/T Factor to the power indicated in the “Exp” (or Exponent) column.  
Calculate the “Value at Meter Base” by multiplying the (M/T Factor w/ Exp) times the (Value at Trf  
Base).  
Q
Loss Watts Percentage Values  
Meter Base kVA  
= 600 * (PT Multiplier) * (CT Multiplier) / 1000  
= 600 * (____________) * (___________) / 1000  
= ________________  
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Q
Calculate Load Loss Values  
Value at Meter Meter Base  
Base kVA  
% Loss at  
Meter Base  
Quantity  
Quantity  
No-Load Loss kW  
No-Load Loss kVAR  
Load Loss kW  
% Loss Watts FE  
% Loss VARs FE  
% Loss Watts CU  
% Loss VARs CU  
Load Loss kVAR  
Enter “Value at Meter Base” from Normalize Losses section. Enter “Meter Base kVA” from previous  
calculation. Calculate “% Loss at Meter Base” by dividing (Value at Meter Base) by (Meter Base kVA)  
and multiplying by 100.  
Enter calculated % Loss Watts values into Nexus meter using Communicator software.  
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Chapter 8  
Nexus Time-of-Use  
8.1: Introduction  
Q
A Time-of-Use (TOU) usage structure takes into account the quantity of energy used and the time at  
which it was consumed. The Nexus 1250/1252 TOU function, available with the Communicator  
EXT software, is designed to accommodate a variety of programmable rate structures. Nexus TOU  
accumulates data based on the time-scheme programmed into the Nexus Monitor.  
Q
See the Communicator EXT User Manual for details on programming the Nexus 1250/1252 20 Year  
TOU calendar and retrieving TOU data.  
8.2: The Nexus TOU Calendar  
Q
A Nexus TOU calendar sets the parameters for TOU data accumulation. You may store up to twenty  
calendars in the Nexus 1250/1252 Monitor and an unlimited amount of calendar files on your  
computer.  
Q
The Nexus TOU calendar profile allows you to assign a programmable usage schedule—eg,  
“Weekday,” “Weekend,” “Holiday”—to each day of the calendar year. You may create up to 16  
different TOU schedules.  
Q
Each TOU schedule divides the 24-hour day into fifteen-minute intervals from 00:00:00 to 23:59:59.  
You may apply one of eight different programmable registers—eg “Peak,” “Off Peak,” “Shoulder  
Peak”— to each fifteen-minute interval.  
Q
The Nexus 1250/1252 Monitor stores:  
•
•
accumulations on a seasonal basis, up to four seasons per year;  
accumulations on a monthly basis.  
Q
Seasonal and monthly accumulations may span one year into the next. Each season and month is  
defined by a programmable start/billing date, which is also the end-date of the prior season or month.  
•
•
A season ends at midnight of the day before the start of the next season.  
A month ends at midnight of the month’s billing day.  
Q
Q
If the year ends and there is no new calendar, TOU accumulations will stop. If a calendar is present  
for the following year, TOU accumulations continue until the next monthly bill date or next  
start-of-season is reached. Accumulation can span into the following year.  
If no following year is present, the last accumulation for the year will end on 12:31:23:59:59.  
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8.3: TOU Prior Season and Month  
Q
The Nexus 1250/1252 Monitor stores accumulations for the prior season and the prior month. When  
the end of a billing period is reached, the current season or month becomes stored as the prior. The  
registers are then cleared and accumulations resume, using the next set of TOU schedules and  
register assignments from the stored calendar.  
Q
Prior and current accumulations to date are always available.  
8.4: Updating, Retrieving and Replacing TOU Calendars  
Q
Communicator EXT software retrieves TOU calendars from the Nexus 1250/1252 Monitor or from  
the computer’s hard drive for review and edit.  
Q
Up to a maximum of twenty yearly calendars can be stored in the Nexus 1250/1252 Monitor at any  
given time. You may retrieve them one at a time; a new calendar can be stored while a current  
calendar is in use.  
Q
Accumulations do not stop during calendar updates. If a calendar is replaced while in use, the  
accumulations for the current period will continue until the set end date. At that point, the current  
time will become the new start time and the settings of the new calendar will be used.  
Q
Reset the current accumulations, if you replace a calendar in use. A reset clears only the current  
accumulation registers. This causes the current accumulations to use the present date as the start and  
accumulate to the next new end date, which will be taken from the new calendar. Once stored, prior  
accumulations are always available and can not be reset. See the Nexus Communicator User Manual  
for how to reset TOU accumulations.  
Q
At the end of a defined period, current accumulations are stored, the registers are cleared and  
accumulations for the next period begin. When the year boundary is crossed, the second calendar, if  
present, is used. To retain continuity, you have up to one year to replace the old calendar with one  
for the following year.  
8.5: Daylight Savings and Demand  
Q
To use Daylight Savings Time, you must enable it in the Nexus Monitor’s Device Profile, Time  
Settings. Click Auto DST, which sets Daylight Savings Time automatically (for the United States  
ONLY). You can also select User Defined and enter the desired dates for Daylight Savings Time.  
See the Communicator EXT User Manual for details.  
Q
To set Demand Intervals, from the Device Profile select Demand Integration and set the desired  
intervals.  
To set Cumulative Demand Type, from the Device Profile click Cold Load Pickup and select  
Block or Rolling Window Average.  
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Chapter 9  
Nexus External I/O Modules  
9.1: Hardware Overview  
Q
All Nexus External I/O modules have the following components:  
•
•
Female RS-485 Side Port: use to connect to another module’s male RS-485 side port.  
Male RS-485 Side Port: use to connect to the Nexus 1250/1252 Meter’s Port 3 or 4 or to  
another module’s female RS-485 side port. See Figure 9.2 for wiring detail.  
•
•
I/O Port: used for functions specific to the type of module; size and pin configuration vary  
depending on type of module.  
Reset Button: Press and hold for three seconds to reset the module’s baud rate to 57600 and its  
address to 247 for 30 seconds.  
•
•
LEDs: when flashing, signal that the module is functioning.  
Mounting Brackets (MBIO): used to secure one or more modules to a flat surface.  
Mounting Brackets (MBIO)  
Female RS-485 Side Port  
LEDs  
I/O Port  
(Size and pin  
configuration vary)  
Integrated Fastening System  
Male RS-485 Side Port  
Reset Button  
Figure 9.1: I/O Module Components  
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9.1.1: Port Overview  
Q
All Electro Industries I/O Modules have ports through which they interface with other devices.  
The port configurations are variations of the four types shown below.  
Four Analog Outputs  
(0-1mA and 4-20mA)  
Eight Analog Outputs  
(0-1mA and 4-20mA)  
Eight Analog Inputs  
(0-1mA, 0-20mA,  
Four Relay Outputs  
or Four KYZ Pulse Outputs  
0-5V , 0-10V  
)
dc  
dc  
or Eight Status Inputs  
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9.2: Installing Nexus External I/O Modules  
Q
I/O modules must use the Nexus 1250/1252 Meter’s Port 3 or 4. Six feet of RS-485 cable harness is  
supplied. Attach one end of the cable to the port (connectors may not be supplied); insert the other  
end into the communication pins of the module’s Male RS-485 Side Port. Follow steps below and  
see Figure 9.2 below. See section 9.3 for details on using multiple I/O modules.  
LED’s  
Male Side Port  
on Nexus I/O  
Module  
R
T
R
T *  
(For runs typically longer than 500 feet)  
Nexus  
1250/1252  
Port 3 or 4  
Figure 9.2: Nexus Meter Connected to I/O Module  
Q
* NOTE: Termination Resistors are only needed with runs typically more than 500 feet. The meter  
has some level of termination internally and usually resistors are not needed.  
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9.2.1: Power Source for I/O Modules  
Q
The Nexus 1250/1252 will supply power to a limited number (3) I/O MODULES. For more, you  
must use an external power source, such as the EIG PSIO (12V). Refer to sections 5.12 and 5.13  
to Determine Power Needed. RS-485 communication is viable for up to 4000 feet (1219 meters).  
You must also do the following:  
1. Connect the A(+) and B(-) terminals on the Nexus to the A(+) and B(-) terminals of the male  
RS-485 port. Connect the shield to the shield (S) terminal. The (S) terminal on the Nexus is  
used to reference the Nexus port to the same potential as the source. It is not an earth ground  
connection. You must also connect the shield to earth-ground at one point.  
2. Put termination resistors at each end, connected to the A(+) and B(-) lines. RT is ~120 Ohms.  
NOTE: Refer to section 5.3 for RT Explanation.  
3. Connect a source of power to the front of the module.  
SIDE LABEL  
1.72”  
TOP LABEL  
Figure 9.3: The PSIO Power Source (Side View)  
showing Male RS-485 Side Port  
Figure 9.4: Power flow from PSIO to I/O Module  
Figure 9.5: Labels for the  
PSIO Power Source  
(Labels are Red & White.)  
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9.3: Using PSIO with Multiple I/O Modules  
LEDs  
Communication  
ONLY  
Female  
RS-485  
(A+, B- and  
Shield)  
Side Port  
Control  
Power  
Reset Button  
Mounting Bracket  
I/O Port (Size and pin configuration vary)  
Figure 9.6: Using PSIO with Multiple I/O Modules  
NOTE: PSIO must be to the right of I/O Modules when viewing the side label (as shown).  
9.3.1: Steps for Attaching Multiple I/O Modules  
1. Each I/O module in a group must be assigned a unique address. See the Communicator EXT  
User Manual for details on configuring and programming the I/O Modules.  
2. Determine how many power sources (such as PSIO) are needed for the number of modules in use.  
See section 9.2.1 for details.  
3. Starting with the left module and using a slotted screw driver, fasten the first I/O Module to the  
left Mounting Bracket. The left Mounting Bracket is the one with the PEM. Fasten the internal  
screw tightly into the left Mounting Bracket.  
4. Next, slide the female RS-485 port into the male RS-485 side port to connect the next I/O  
module to the left module. Fasten together enough to grab but do not tighten.  
One by one combine the modules together using the Integrated Fastening System (Fig. 9.1).  
If you require an additional power supply, attach a PSIO (power supply) to the right of each  
group of 4 I/O Modules (section 9.3).  
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NOTE: The PB1 can also be used for a Low Voltage Power Supply. It must be mounted  
separately.  
5. Once you have combined all the I/O modules together for the group, fasten tightly.  
This final tightening will lock the whole group together as a unit.  
6. Attach the right Mounting Bracket to the right side of the group using small phillips head screws  
provided.  
7. Then, mount the group of modules on a secure, flat surface. This procedure will ensure that all  
modules stay securely connected.  
9.4: Factory Settings and Reset Button  
Q
Factory Settings:  
All Nexus I/O Modules are shipped with a preset address and a baud rate of 57600. See below for  
addresses.  
Q
Reset Button:  
If there is a communication problem or if you are unsure of a module’s address and baud rate, press  
and hold the RESET button for 3 seconds; the module will reset to a default address of 247 at 57600  
baud rate for 30-seconds. This will enable you to interrogate the I/O using the Communicator EXT  
software; see the Modbus Communicating I/O Modules User Manual.  
Model #  
Module  
Factory-Set Address  
1mAON4  
1mAON8  
20mAON4  
20mAON8  
8AI1  
0±1mA, 4-Channel Analog Output  
0±1mA, 8-Channel Analog Output  
4–20mA, 4-Channel Analog Output  
4–20mA, 8-Channel Analog Output  
0±1mA, 8-Channel Analog Input  
0±20mA, 8-Channel Analog Input  
128  
128  
132  
132  
136  
140  
144  
8AI2  
8AI3  
0±5V , 8-Channel Analog Input  
dc  
8AI4  
0±10V , 8-Channel Analog Input  
dc  
148  
4RO1  
4PO1  
8DI1  
4 Latching Relay Outputs  
4 KYZ Pulse Outputs  
8 Digital Status Inputs (Wet/Dry)  
156  
160  
164  
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9.5: Analog Transducer Signal Output Modules  
Analog Transducer Signal Output Modules Specifications  
1mAON4: 4-Channel Analog Output, 0±1mA  
1mAON8: 8-Channel Analog Output, 0±1mA  
20mAON4: 4-Channel Analog Output, 4–20mA  
20mAON8: 8-Channel Analog Output, 4–20mA  
0.1% of Full Scale  
Model Numbers  
Accuracy  
Scaling  
Programmable  
RS-485, Modbus RTU  
Communication  
Programmable Baud Rates: 4800, 9600, 19200, 57500  
15–20V at 50–200mA;  
dc  
Nexus 1250/1252 Unit  
Power Requirement  
supports up to 2 Modules  
Operating Temperature  
(-20 to 79)°C / (-4 to +158)°F  
Maximum Load Impedance  
0±1mA: 10k Ω; 4–20mA: 500 Ω  
Modbus Address:  
1mAON4, 0-1mA: 128 1mAON8, 0-1mA: 128  
20mAON4, 4–20mA: 132, 20mAON8, 4-20mA: 132  
Factory Settings  
Baud Rate: 57600  
Transmit Delay Time: 0  
Modbus Address: 247  
Baud Rate: 57600  
Default Settings  
(Reset Button)  
Transmit Delay Time: 20 csec  
9.5.1: Overview  
Q
The Analog Transducer Signal Output Modules (0±1mA or 4–20mA) are available in either a 4- or  
8-channel configuration. Maximum registers per request, read or write, is 17 registers.  
Q
Nexus 1250/1252 Unit supplies power for up to two connected Analog Output modules. See  
section 9.2 for power and communication details. Refer to sections 5.12 - 5.13 to determine if you  
must use an additonal power source, such as the EIG PSIO.  
Q
All outputs share a single common point. This is also an isolated connection (from ground).  
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Q
The Modbus Map for the Analog Output Module (and operating details) can be found in the Modbus  
Communicating I/O Modules Manual.  
9.5.2: Normal Mode  
Q
Normal Mode is the same for the 0-1mA and the 4-20mA Analog Output Modules except for the  
number of processes performed by the modules.  
Both devices:  
1. Accept new values through communication.  
2. Output current loops scaled from previously accepted values.  
The 0-1mA module includes one more process in its Normal Mode:  
3. Read and average the A/D and adjust values for Process 2 above.  
.
Q
The device will operate with the following default parameters:  
Address  
Baud Rate  
Transmit Delay Time  
247 (F7H)  
57600 Baud  
0
Q
Normal Operation is prevented by a number of occurrences. See section 9.4.1 for details.  
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9.6: Analog Input Modules  
Analog Input Modules Specifications  
8AI1: 8-Channel Analog Input, 0±1mA  
8AI2: 8-Channel Analog Input, 0±20mA  
Model Numbers  
8AI3: 8-Channel Analog Input, 0±5V  
dc  
8AI4: 8-Channel Analog Input, 0±10V  
dc  
Accuracy  
Scaling  
0.1% of Full Scale  
Programmable  
RS-485, Modbus RTU  
Communication  
Programmable Baud Rates: 4800, 9600, 19200,57600  
15-20V at 50-200mA;  
dc  
Nexus 1250/1252 Unit  
Power Requirement  
supports up to 4 Modules  
Operating Temperature  
(-20 to 79)°C / (-4 to +158)°F  
Maximum Load  
Impedance  
0-1mA: 10k Ω; 4-20mA: 500 Ω  
Modbus Address:  
8AI1, 0±1mA: 136; 8AI2, 0±20mA: 140  
8AI3, 0±5V : 144, 8AI4, 0±10V : 148  
dc  
dc  
Factory Settings  
Baud Rate: 57600  
Transmit Delay Time: 0  
Modbus Address: 247  
Baud Rate: 57600  
Default Settings  
(Reset Button)  
Transmit Delay Time: 20 csec  
9.6.1: Overview  
Q
The Analog Input Modules (0±1mA, 0±20mA, 0±5V and 0±10V ) are available in 8-channel  
dc dc  
format. Maximum registers per request, read or write, is 17 registers.  
Q
Q
Nexus 1250/1252 Unit supplies power for up to 4 connected Analog Input modules. See section 9.2  
for power and communication details. Refer to sections 5.12 - 5.13 to determine if you must use an  
additonal power source, such as the EIG PSIO.  
All inputs share a single common point. This is also an isolated connection (from ground).  
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Q
The Modbus Map for the Analog Output Module (and operating details) can be found in the Modbus  
Communicating I/O Modules Manual.  
9.6.2: Normal Mode  
Q
In Normal Mode, the Input Module:  
1. Reads and averages the A/D and adjusts values for process 2.  
2. Calculates the percentage of Input Value.  
NOTE: The percentage value of the Input will be stored in Input Value Registers (Registers  
04097-04104).  
.
Q
The device will operate with the following default parameters:  
Address  
Baud Rate  
Transmit Delay Time  
247 (F7H)  
57600 Baud  
0
Q
Normal Operation is prevented by a number of occurrences. See section 9.4.1 for details.  
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9.7: Digital Dry Contact Relay Output (Form C) Module  
Digital Dry Contact Relay Output (Form C) Module Specifications  
Model Number  
Accuracy  
4RO1: 4 Latching Relay Outputs  
0.1% of Full Scale  
Scaling  
Programmable  
RS-485, Modbus RTU  
Communication  
Programmable Baud Rates: 4800, 9600, 19200, 57600  
15–20V at 50–200 mA;  
dc  
Nexus 1250/1252 Unit  
Power Requirement  
supports up to 4 Modules  
Operating Temperature  
(-20 to 79)°C / (-4 to +158)°F  
0-1mA: 10k Ω; 4-20mA: 500 Ω  
Modbus Address: 156  
Maximum Load Impedance  
Factory Settings  
Baud Rate: 57600  
Transmit Delay Time: 0  
Modbus Address: 247  
Default Settings  
(Reset Button)  
Baud Rate: 57600  
Transmit Delay Time: 20 csec  
9.7.1: Overview  
Q
The Relay Output Module consists of four Latching Relay Outputs. In Normal Mode, the device  
accepts commands to control the relays. Relay output modules are triggered by limits programmed  
with the Communicator EXT software. See the Communicator EXT User Manual for details on  
programming limits.  
Q
Nexus 1250/1252 Unit supplies power for up to 4 connected Relay Output modules. See section 9.2  
for power and communication details. Refer to sections 5.12 - 5.13 to determine if you must use an  
additonal power source, such as the EIG PSIO.  
Q
Q
The Modbus Map for the Analog Output Module (and operating details) can be found in the Modbus  
Communicating I/O Modules Manual.  
Each latching relay will hold its state in the event of a power loss.  
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9.7.2: Communication  
Q
Maximum registers per request, read or write, is 4 registers.orm  
Q
The device will operate with the following Default Parameters:  
Address  
247 (F7H)  
Baud Rate  
57600 Baud  
Transmit Delay Time 20 csec  
Q
Some situations will cause the device to operate with the above Default Parameters. See section  
9.4.1 for details of Default Mode.  
9.7.3: Normal Mode  
Q
Normal Mode consists of one process:  
1. The device accepts new commands to control the relays.  
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9.8: Digital Solid State Pulse Output (KYZ) Module  
Digital Solid State Pulse Output (KYZ) Module Specifications  
Model Number  
4PO1  
RS-485, Modbus RTU  
Communication  
Programmable Baud Rates: 4800, 9600, 19200, 57600  
15–20V at 50–200 mA;  
dc  
Nexus 1250/1252 Unit  
Power Requirement  
supports up to 4 Modules  
Operating Temperature  
Voltage Rating  
(-20 to 79)°C / (-4 to +158)°F  
Up to 300V  
dc  
Commands Accepted  
Read and Write with at least 4 registers of data per command  
256 byte I2C EEPROM  
for storage of Programmable Settings and Nonvolatile Memory  
Memory  
Modbus Address: 160  
Baud Rate: 57600  
Factory Settings  
Transmit Delay Time: 0  
Modbus Address: 247  
Baud Rate: 57600  
Default Settings  
(Reset Button)  
Transmit Delay Time: 20 csec  
9.8.1: Overview  
Q
The KYZ Pulse Output Modules have 4 KYZ Pulse Outputs and accept Read and Write Commands  
with at least 4 registers of data per command. Digital Solid State Pulse Output (KYZ) Modules are  
user programmed to reflect VAR-hours, WATT-hours, or VA-hours. See the Modbus Communicating  
I/O Modules User Manual for details on programming the module.  
Q
Nexus 1250/1252 Unit supplies power for up to 4 connected KYZ Pulse Output modules. See  
section 9.2 for power and communication details. Refer to sections 5.12 - 5.13 to determine if you  
must use an additonal power source, such as the EIG PSIO.  
Q
Q
The Modbus Map for the KYZ Pulse Output Module (and operating details) can be found in the  
Modbus Communicating I/O Modules Manual.  
NC = Normally Closed; NO = Normally Open; C = Common.  
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9.8.2: Communication  
Q
Maximum registers per request, read or write, is 4 registers.orm  
Q
The device will operate with the following Default Mode Parameters. See section 9.4.1 for details.  
Address  
247 (F7H)  
Baud Rate  
57600 Baud  
Transmit Delay Time 20 csec  
9.8.3: Normal Mode  
Q
Energy readings are given to the device frequently. The device generates a pulse at each channel  
after a certain energy increase.  
Q
Normal Operation consists of three processes:  
1. The first process accepts writes to registers 04097 - 04112. Writes can be up to four registers  
long and should end on the fourth register of a group (register 04100, or registers 04103-04112  
or registers 04109-04112). These writes can be interpreted as two-byte, four-byte, six-byte or  
eight-byte energy readings. The reception of the first value for a given channel provides the  
initial value for that channel. Subsequent writes will increment the Residual for that channel by  
the difference of the old value and the new value. The previous value is then replaced with the  
new value. Attempting to write a value greater than the programmed Rollover Value for a given  
channel is completely ignored and no registers are modified. If the difference is greater than half  
of the programmed Rollover Value for a given channel, the write does not increment the Residual  
but does update the Last Value. Overflow of the Residual is not prevented.  
2. The second process occurs in the main loop and attempts to decrement the Residual by the  
Programmed Energy/Pulse Value. If the Residual is greater than the Programmed Energy/Pulse  
Value and the Pending Pulses Value for that channel is not maxed, then Residual is decremented  
appropriately and the Pending Pulses is incremented by two, signifying two more transitions and  
one more pulse.  
3. The third process runs from a timer which counts off pulse widths from the Programmable  
Minimum Pulse Width Values. If there are Pulses Pending for a channel and the delay has  
passed, then the Pulses Pending is decremented for that channel and the Output Relay is toggled.  
Q
Operation Indicator (0000H = OK, 1000H = Problem):  
Bit 1: 1 = EEPROM Failure  
Bit 2: 1 = Checksum for Communications Settings bad  
Bit 3: 1 = Checksum for Programmable Settings bad  
Bit 4: 1 = 1 or mor Communications Settings are invalid  
Bit 5: 1 = 1 or more Programmable Settings are invalid  
Bit 6: 1 = 1 or more Programmable Settings have been modified  
Bit 7: 1 = Forced Default by Reset Value  
Bit 15: 1 = Normal Operation of the device is disabled  
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9.9: Digital Status Input Module  
Digital Status Input Module Specifications  
Model Number  
8DI1  
RS-485, Modbus RTU  
Communication  
Programmable Baud Rates: 4800, 9600, 19200, 57600  
15–20V at 50–200 mA;  
dc  
Nexus 1250/1252 Unit  
Power Requirement  
supports up to 4 Modules  
Operating Temperature  
Voltage Rating  
Detection  
(-20 to 79)°C / (-4 to +158)°F  
Up to 300V  
dc  
Wet/Dry, Auto Detect  
2
256 byte I C EEPROM for storage of Programmable  
Memory  
Settings and Nonvolatile Memory  
Modbus Address: 164  
Factory Settings  
Baud Rate: 57600  
Transmit Delay Time: 0  
Modbus Address: 247  
Default Settings  
(Reset Button)  
Baud Rate: 57600  
Transmit Delay Time: 20 csec  
9.9.1: Overview  
Q
The Digital Status Input Module is used for either additional status detect or for accumulating pulses  
from external equipment, such as power meters, water meters, etc.  
Q
Nexus 1250/1252 Unit supplies power for up to 4 connected Digital Status Input modules. See  
section 9.2 for power and communication details. Refer to sections 5.12 - 5.13 to determine if you  
must use an additonal power source, such as the EIG PSIO.  
9.9.2: Communication  
Q
Maximum registers per request, read or write, is 4 registers.orm  
Q
The device will operate with the following Default Mode Parameters. See section 9.4.1 for details.  
Address  
247 (F7H)  
Baud Rate  
57600 Baud  
Transmit Delay Time 20 csec  
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9.9.3: Normal Mode  
Q
The device is polling the inputs at 100Hz (once every 10 msec), debouncing the inputs and  
incrementing the Transition Accumulators for each channel as appropriate.  
The inputs are represented by Channel 1 in the LSB through Channel 8 in the MSB of the low order  
byte of the register.  
Q
The Modbus Map for the Digital Status Input Modules (and operating details) can be found in the  
Modbus Communicating I/O Modules Manual.  
9.10: Specifications  
Q
The following multiple analog or digital I/O modules mount externally to the Nexus Socket Meter.  
The Nexus 1262 and 1272 Units DO NOT SUPPORT I/O MODULES. Use an additional power  
supply, such as PSIO, to provide I/O capability. See Chapter 6 for mounting diagrams.  
Q
Analog Transducer Signal Outputs (Up to two modules can be used with the Nexus.)  
1mAON4: 4 Analog Outputs, scalable, bidirectional.  
1mAON8: 8 Analog Outputs, scalable, bidirectional.  
20mAON4: 4 Analog Outputs, scalable.  
20mAON8: 8 Analog Outputs, scalable.  
Q
Analog Transducer Inputs (Multiple modules can be used.)  
8AI1: 8 Analog Inputs 0–1mA, scalable and bidirectional.  
8AI2: 8 Analog Inputs 0–20mA, scalable and bidirectional.  
8AI3: 8 Analog Inputs 0–5V , scalable and bidirectional.  
dc  
8AI4: 8 Analog Inputs 0–10V , scalable and bidirectional.  
dc  
Q
Digital Dry Contact Relay Outputs (Multiple modules can be used.)  
4RO1: 4 Relay Outputs 10 Amps, 125V , 30V , Form C.  
ac  
dc  
Q
Q
Digital Solid State Pulse Outputs (Multiple modules can be used.)  
4PO1: 4 Solid State Pulse Outputs, Form A KYZ pulses.  
Digital Inputs (Multiple modules can be used.)  
8DI1: 8 Digital status inputs Wet/Dry Auto Detect, up to 300V .  
dc  
Q
Other I/O Accessories  
PSIO: External Power Supply which is necessary if you are connecting more than 2 to 4 I/O  
modules to a Nexus 1250/1252 Meter. The number is determined by the type of I/O  
Module.  
MBIO: Bracket for surface-mounting I/O modules to any enclosure.  
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Chapter 10  
Nexus Monitor with Internal Modem Option  
10.1: Hardware Overview  
Q
The Nexus 1250/1252 Monitor with the INP2, Internal Modem Option, has all the components of the  
standard Nexus Monitor PLUS the cabability of connecting to a PC via standard phone line. No  
additional hardware is required to establish a virtually unlimited connection from a PC to a Nexus  
1250/1252 with INP2, Internal Modem Option.  
If desired, the internal expansion port of the Nexus 1250/1252 can be configured with an internal  
56K bps modem. This gives Nexus Dial-In and Dial-Out capability without additional hardware.  
This is ideal for small remote applications.  
When the device is configured with INP2 , Port 2 becomes a gateway allowing other Modbus-based  
serial devices access to the phone line. Additional connections can include a daisy chain of standard  
Nexus Monitors. A Daisy Chain can include up to 31 meters. If more are desired, the installation of  
a repeater allows additional meters. (See section 5.14 for repeater details.)  
RS-485  
RJ-11  
Daisy Chain  
Originate Modem  
PC  
(or Internal to PC)  
Figure 10.1: Nexus with Internal Modem Option  
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10.2: Hardware Connection  
Q
Use RJ-11 Standard Telephone Line to connect with an INP2 Option Nexus. The RJ-11 line is  
inserted into the RJ-11 Port on the face of the Nexus 1250/1252 with Internal Modem Option. The  
connection using RJ-11 into the Nexus is virtually unlimited, since it utilizes a PSTN (Public  
Switched Telephone Network). To connect with other Nexus 1250/1252 Monitors in either local or  
remote locations, you MUST use Port 2 as a Master and an RS-485 connection to any port on the  
remote Nexus. The Address of the remote Nexus MUST be something other than “1”. The link  
using RS-485 is viable for up to 4000 feet (1219 meters).  
10.3: Dial-In Function  
Q
The modem continuously monitors the telephone line to detect an incoming call. When an  
incoming call is detected, the modem will wait a user-set number of rings and answer the call. The  
modem can be programmed to check passwords and lock out unsuccessful attempts to connect.  
When an incoming call is successfully connected, the control of communications is passed to the  
calling software program. The modem will respond to computer demands to download data or  
perform other actions authorized by the meter passwords.  
10.4: Dial-Out Function  
Q
The Dial-Out Function is intended to allow the meter to automatically report certain conditions  
without user intervention. The modem is normally polling the meter to determine if any abnormal  
or reportable conditions exist. The modem checks the following meter conditions and programmed  
events (set in Nexus Communicator) to determine if a call should be placed.  
•
•
•
•
•
•
•
•
•
•
Are any meter set-point limits exceeded?  
Has status of high-speed inputs changed?  
Has waveform been recorded?  
Has power quality event been recorded?  
Has a control output changed?  
Is either history log approaching a full condition?  
Is the event log approaching a full condition?  
Is any other log approaching a full condition?  
Has the Modem Password failed?  
Has Communication with the Nexus failed?  
Q
Q
If any of the monitored events exist, the modem will automatically initiate a call to a specified  
location to make a report or perform some other function. For log full conditions, the meter will  
automatically download the log(s) that are nearing the full state. The modem can be programmed to  
call two different numbers to make the required reports, Primary and Backup.  
The modem can be programmed with an ASCII string for identification purposes. If this string is  
present, the modem will play the string to the host computer upon connection to identify the meter  
to the host software.  
Refer to the Communicator EXT Software Manual for programming details.  
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Chapter 11  
Nexus Meter with Internal Network Option  
11.1: Hardware Overview  
Q
The Nexus 1250/1252 Meter with the Internal Network Option has all the components of the  
standard Nexus Meter PLUS the cabability of connecting to a multiple PC’s via Modbus/TCP over  
Ethernet. Additional hardware is not required to establish a connection from a network to a Nexus  
with Internal Network Option.  
With the Internal Network Option, the Nexus 1250/1252 provides an Ethernet Gateway, allowing  
access to other Modbus/RTU devices. Additional connections can include a daisy chain of standard  
Nexus Meters. A daisy chain can include up to 31 meters. If more are desired, the installation of a  
repeater allows additional meters. (See section 5.15 for repeater details.)  
MODBUS/RTU  
RS-485  
10/100BaseT  
or 10BaseT  
RJ-45  
MODBUS/TCP  
over Ethernet  
Daisy Chain  
Network  
Figure 11.1: Nexus with Internal Network Option  
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Q
The Internal Network Option of the Nexus Meter is an extremely versatile communications tool.  
·
·
·
·
·
Adheres to IEEE 802.3 ethernet standard using TCP/IP.  
Utilizes simple and inexpensive 10/100BaseT wiring and connections.  
Plugs right into your network using built-in RJ-45 jack.  
Programmable to any IP address, subnet mask and gateway requirements.  
Communicates using the industry standard Modbus/TCP protocol.  
Q
With the Internal Network Option, the standard Port 2 on the Nexus 1250/1252 becomes a  
“gateway” to allow additional Nexus Meters access via the LAN. Simply connect a daisy chain of  
Nexus Meters together via RS-485, each with its own device address and using the same baud rates.  
With this option, you can access any of those instruments via the single LAN connection.  
Q
Q
The Internal Network Option allows multiple simultaneous connections (via LAN) to the Nexus.  
You can access the Nexus with SCADA, MV90 and RTU all at the same time.  
The Internal Network Option allows multiple users running Communicator EXT software to access  
the meter concurrently.  
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11.2: Hardware Connection  
Q
Use Standard RJ-45 10/100BaseT cable to connect with the Nexus 1250/1252. The RJ-45 line is  
inserted into the RJ-45 Port on the face of the Nexus with Internal Network Option.  
Q
Set the IP Address using the following steps:  
(Refer to Section 3.5 of the Communicator EXT User Manual for more details).  
1. From the Device Profile screen, double-click on the Communications Ports line, then double-  
click on any of the ports. The Device Profile Communications Settings screen appears.  
2. In the Network Settings section, enter data provided by your systems manager:  
IP Address:  
10.0.0.1 (Example)  
Subnet Mask:  
Default Gateway:  
Computer Name:  
Baud Rate:  
255.255.255.0 (Example)  
0.0.0.0  
NETWORK (Example)  
115200 (Example)  
(Example)  
NOTE: DO NOT check Obtain IP Address using DHCP Server, if you have an IP Address.  
Q
After the above parameters are set, Communicator EXT will connect via the network using a Device  
Address of “1” and the assigned IP Address using the following steps:  
1. Double click on Communicator EXT icon to open.  
2. Click the Connect icon in the icon tool bar. The Connect screen will appear.  
3. Click the Network button at the top of the screen. The screen will change to one requesting the  
following information:  
Device Address:  
Host:  
1
IP Address (per your network adminitrator).  
Example: 10.0.0.1  
502  
Modbus TCP  
Network Port:  
Protocol:  
4. Click the Connect button at the bottom of the screen. Communicator EXT connects to the  
Nexus with the Host IP Address via the Network.  
Q
Q
Q
To connect with other Nexus Meters in either local or remote locations, you MUST use the  
Ethernet Gateway as a Master and an RS-485 connection to any port on the remote Nexus.  
The Address of the remote Nexus MUST be something other than “1”. “1” is reserved for the  
Nexus connected to the network via its RJ-45.  
The link using RS-485 is viable for up to 4000 feet (1219 meters).  
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Chapter 12  
Flicker  
12.1: Overview  
Flicker is the sensation that is experienced by the human visual system when it is subjected to  
changes occurring in the illumination intensity of light sources. The primary effects of flicker are  
headaches, irritability and sometimes epilepsy.  
IEC 61000-4-15 and former IEC 868 describe the methods used to determine flicker severity. This  
phenomenon is strictly related to the sensitivity and the reaction of individuals. It can only be  
studied on a statistical basis by setting up suitable experiments among people.  
12.2: Theory of Operation  
Flicker can be caused by voltage variations which are caused by variable loads, such as arc furnaces,  
laser printers and microwave ovens. In order to model the eye brain change, which is a complex  
physiological process, the signal from the power network has to be processed while conforming with  
Figure 16.1 below.  
•
Block 1 consists of scaling circuitry and an automatic gain control function that normalizes input  
voltages to Blocks 2, 3 and 4. For the specified 50 Hz operation, the voltage standard is 230 V  
RMS.  
•
•
Block 2 recovers the voltage fluctuation by squaring the input voltage scaled to the reference  
level. This simulates the behavior of a lamp.  
Block 3 is composed of a cascade of two filters and a measuring range selector. In this  
implementation, a log classifier covers the full scale in use so the gain selection is automatic and  
not shown here. The first filter eliminates the DC component and the double mains frequency  
components of the demodulated output.  
The configuration consists of a .05 Hz Low High Pass filter and a 6 Pole Butterworth Low Pass  
filter located at 35 Hz. The second filter is a weighting filter that simulates the response of the  
human visual system to sinusoidal voltage fluctuations of a coiled filament, gas-filled lamp (60  
W - 230 V). The filter implementation of this function is as specified in IEC 61000-4-15.  
•
•
Block 4 is composed of a squaring multiplier and a Low Pass filter. The Human Flicker  
Sensation via lamp, eye and brain is simulated by the combined non-linear response of Blocks 2,  
3 and 4.  
Block 5 performs an online statistical cumulative probability analysis of the flicker level. Block  
5 allows direct calculation of the evaluation parameters Pst and Plt.  
Q
Flicker Evaluation occurs in the following forms: Instantaneous, Short Term or Long Term. Each  
form is detailed below:  
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•
•
Instantaneous Flicker Evaluation  
An output of 1.00 from Block 4 corresponds to the Reference Human Flicker Perceptibility  
Threshold for 50% of the population. This value is measured in Perceptibility Units (PU) and is  
labeled Pinst. This ia a real time value and it is continuously updated.  
Short Term Flicker Evaluation  
An output of 1.00 from Block 5 (corresponding to the Pst value) corresponds to the conventional  
threshold of irritability per IEC 1000-3-3. In order to evaluate flicker severity, two parameters  
have been defined: one for the short term called Pst (defined in this section) and one for the long  
term called Plt (defined in the next section).  
The standard measurement time for Pst is 10 minutes. Pst is derived from the time at level  
statistics obtained from the level classifier in Block 5 of the flicker meter. The following  
formula is used:  
P
=
0.0314  
P
+
0.0525Ps  
+
0.0657P s  
+
0.28  
P
+
0.08P  
50  
st  
0.1  
1
3
10  
s
s
Where the percentiles P(0.1), P(1), P(3), P(10), P(50) are the flicker levels exceeded for 0.1, 1, 2,  
20 and 50% of the time during the observation period. The suffix S in the formula indicates that  
the smoothed value should be used. The smoothed values are obtained using the following  
formulas:  
P(1s) = (P(.7) + P(1) + P(1.5))/3  
P(3s) = (P(2.2) + P(3) + P(4))/3  
P(10s) = (P(6) + P(8) + P(10) + P(13) + P(17))/5  
P(50s) = (P(30) + P(50) + P(80))/3  
The .3-second memory time constant in the flicker meter ensures that P(0.1) cannot change  
abruptly and no smoothing is needed for this percentile.  
•
Long Term Flicker Evaluation  
The 10-minute period on which the short-term flicker severity is based is suitable for short duty  
cycle disturbances. For flicker sources with long and variable duty cycles (e.g. arc furnaces) it is  
necessary to provide criteria for long-term assessment. For this purpose, the long-term Plt is  
derived from the short-term values over an appropriate period. By definition, this is 12  
short-term values of 10 minutes each over a period of 2 hours. The following formula is used:  
N
P3  
∑
sti  
3
i=  
1
P
=
lt  
N
Where P (i = 1, 2, 3, ...) are consecutive readings of the short-term severity P .  
sti st  
Q
Summary  
Flicker = Changes in the illumination of light sources due to cyclical voltage variations.  
Pinst = Instantaneous flicker values in Perceptibility Units (PU).  
Pst = Value based on 10-minute analysis.  
Plt = Value based on 12 Pst values.  
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Measurement Procedure  
1. Original Signal with amplitude variations.  
2. Square demodulator.  
3. Weighted filter.  
4. Low pass filter 1st order.  
5. Statistical computing.  
Q
Data available  
Pst, Pst Max, Pst Min values for long term recording  
Plt, Plt Max, Plt Min values for long term recording  
Simulation Of Eye Brain Response  
Block 1  
Block 2  
Block 3  
Block 4  
Block 5  
Voltage  
Detector  
and Gain  
Control  
High Pass  
Filter  
(DC  
A/D  
Converter  
Sampling  
Rate  
Minimum  
64 level  
Classifier  
Output  
Interface  
1st  
Square  
Law  
Demodulator  
Removal)  
Order  
Sliding  
Mean  
Filter  
Weighting  
Filter  
Squaring  
Multiplier  
>50Hz  
Low  
Pass Filter  
(Carrier  
Input  
Voltage  
Adaptor  
Removal  
Programming of short and  
long observation periods  
Output Recording  
Output and Data Display  
Pst Max/Min Pst  
Plt Max/Min Plt  
Instantaneous Flicker in  
Perceptibility Units  
(Pinst)  
Figure 12.1: Simulation of Eye Brain Response  
12.3: Setup  
Initially the user must set up several parameters to properly configure Flicker. Using Communicator  
EXT, from the Icon Menu select Edit Device Profile. From the Device Profile, select Flicker  
Settings. The following screen will appear:  
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•
•
Select a Pst time range from 1 to 10 minutes. The standard measurement period is nominally 10  
minutes.  
Select a Plt time range from 1 to 240 minutes. The standard measurement is nominally 12 Pst  
periods (120 minutes). Plt time must always be equal to or great than and a multiple of Pst time.  
This is reflected in the selections available to the user.  
•
Select the frequency of operation. 50 Hz is the approved frequency according to Flicker  
standards. A 60 Hz implementation is available and can be selected. This implementation is the  
proposed 60 Hz standard that is still in the approval process.  
Remember the voltage is normalized. For 50 Hz, the normalized voltage is 230 V and for 60 Hz,  
the normalized voltage is 120 V.  
Press OK when you are finished.  
Press Help for more information on this topic.  
12.4: Software - User Interface  
Q
Main screen  
From the Communicator EXT Icon Menu select Real Time Poll, Flicker. The following screen  
appears:  
This section describes the Main Screen functions. The available values (Instantaneous, Short Term,  
Long Term) will be described below.  
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Time  
Start/Reset is the time when Flicker was started or reset. A Reset of Flicker causes the Max/Min  
values to be cleared and restarts the Flicker Pst and Plt timers. A Start of Flicker is also  
equivalent to a Reset in that the PST and PLT are restarted and the Max/Min Values are cleared.  
Stop corresponds to the time when Flicker is turned off.  
Current is the current clock time.  
Next Pst is the countdown time to when the next Pst value is available.  
Next Plt is the countdown time to when the next Plt value is available.  
Status  
Indicates the current status. Active = On. Stopped = Off.  
Frequency  
Base is the current operating frequency selected by the user (50 or 60 Hz).  
Current is the real time frequency measurement of the applied voltage.  
Base Voltage is the normalized voltage for the selected frequency (230 V for 50 Hz or 120 V for  
60 Hz).  
Flicker Monitoring  
Clicking on Stop causes Flicker to stop being processed and freezes all the current values. Stop  
Time is recorded and clears the current Max/Min Values  
Clicking on Start starts Flicker processing. Start Time is recorded.  
Clicking on Reset causes the Max/Min values to be cleared and restarts the Flicker Pst and Plt  
timers.  
Click OK to exit the Flicker screen.  
Click Help for more information on this topic.  
Q
Instantaneous Readings  
Refer to the Instantaneous section of the Main screen above. If you are on the Short or Long Term  
screens, click on the Instantaneous tab to display the Instantaneous screen. The PU values, Pinst for  
Voltage Inputs Va, Vb and Vc are displayed here and are continuously updated. The corresponding  
Current Voltage values for each channel are displayed for reference.  
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Short Term Readings  
Click on the Short Term tab to access the screen containing three groups of Pst readings.  
Pst Readings Displayed  
•
•
•
Current Pst values for Va, Vb and Vc and the time of computation.  
Current Pst Max values for Va, Vb and Vc since the last reset and the time of the last reset.  
Current Pst Min values for Va, Vb and Vc since the last reset and the time of the last reset.  
The following screen is displayed:  
Q
Long Term Readings  
Click on the Long Term tab to access the Plt readings. The screen below displays three groups of  
Plt values.  
Plt Readings Displayed  
•
•
•
Current Plt values for Va, Vb and Vc and the time of computation.  
Current Plt Max values for Va, Vb and Vc since the last reset and the time of the last reset.  
Current Plt Min values for Va, Vb and Vc since the last reset and the time of the last reset.  
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12.5: Logging  
The Nexus is capable of logging Flicker values in an independent log. When Flicker is on, entries  
are made into the log in accordance with the times that associated values occur. Pst, Pst Max, Pst  
Min, Plt, Plt Max, Plt Min, Start/Reset and Stop times are all recorded. All values can be down-  
loaded to the Log Viewer where they are available for graphing or export to another program, such  
as Excel. All Flicker values are predefined and cannot be changed.  
12.6: Polling  
The Pinst, Pst, Pst Max, Pst Min, Plt, Plt Max, Plt Min values are all capable of being polled  
through the Communications Port. Refer to the Nexus Modbus and DNP Mappings for register  
assignments and data definitions.  
12.7: Log Viewer  
From the Communicator EXT Log Viewer screen, using the menus at the top of the Log Viewer  
screen, select a meter, time ranges and values to access. Select Flicker.  
The values and the associated time stamps (when the values occurred) are displayed in a grid box.  
Use the buttons at the bottom of the screen to create a graph or export the data to another program.  
Max and Min values are only displayed; they cannot be graphed. But, Max and Min values are  
available for export.  
Graphed values include Pst and Plt Va, Vb and Vc.  
Displayed values include Pst and Plt Max and Min for Va, Vb and Vc.  
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12.8: Performance Notes  
Pst and Plt average time are synchronized to the clock (e.g. for a 10 minute average, the times will  
occur at 0, 10, 20, etc.). The actual time of the first average can be less than the selected period to  
allow for initial clock synchronization.  
If the wrong frequency is chosen (e.g. 50Hz selection for a system operating at 60Hz), Flicker will  
still operate but the values computed will not be valid. Select carefully.  
User settings are stored. If Flicker is on and power is removed from the meter, Flicker will still be  
on when power returns. This can cause data gaps in the logged data.  
The Max and Min values are stored and are not lost if the unit is powered down.  
Flicker meets the requirements of IEC 61000-4-15 and former IEC 868. Refer to those  
specifications for more details, if needed.  
Operation is at 230V for 50Hz and 120V for 60Hz as per specification. If the input voltage is  
different, the system will normalize it to 230V or 120V for computational purposes.  
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Appendix A  
Transformer Loss Compensation Excel Spreadsheet  
with Examples  
A.1: Calculating Values  
Q
Transformer Loss Compensation is discussed in Chapter 7 of this manual. Values for three element  
installations can be calculated in two ways:  
•
Click the TLC Calculator button on the Transformer Loss screen of the Nexus Device Profile.  
The TLC Calculator button activates an Excel Spreadsheet, ONLY if you have MS Excel  
installed on your computer. A copy of the Excel Spreadsheet is offered on the following  
pages with example numbers.  
1. Enter the required data into the Excel Spreadsheet. The Excel program will calculate the  
values needed for the Transformer Loss screen of the Device Profile.  
2. Enter the values into the Device Profile.  
•
Use the worksheet found in Chapter 7, “Three Element Loss Compensation Worksheet” to  
calculate the values by hand. Notes under each section will assist you.  
1. Enter values based on the tranformer manufacturer’s test report. The worksheet is  
progressive and notes under each section will guide you to the next section.  
2. Enter the values into the Device Profile.  
A.2: Excel Spreadsheet with Example Numbers  
Q
If you have MS Excel installed in your computer, use the TLC Calculator button on the Transformer  
Loss screen of the Device Profile. The copy of the Spreadsheet with Example Numbers found on the  
following pages will assist you.  
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Glos s ary  
0.1 Second Values:  
1 Second Values:  
These values are the RMS values of the indicated quantity as calculated after  
approximately 50 milliseconds (3 cycles) of sampling.  
These values are the RMS values of the indicated quantity as calculated after  
one second (60 cycles) of sampling.  
Alarm:  
An event or condition in a meter that can cause a trigger or call-back to occur.  
Annunciator:  
A short label that identifies particular quantities or values displayed, for example  
kWh.  
Average (Current):  
When applied to current values (amps) the average is a calculated value that  
corresponds to the thermal average over a specified time interval. The interval  
is specified by the user in the meter profile. The interval is typically 15 minutes.  
So, Average Amps is the thermal average of amps over the previous 15-minute  
interval. The thermal average rises to 90% of the actual value in each time  
interval. For example, if a constant 100amp load is applied, the thermal average  
will indicate 90 amps after one time interval, 99 amps after two time intervals  
and 99.9 amps after three time intervals.  
Average (Input Pulse When applied to Input Pulse Accumulations, the “Average” refers to the block  
Accumulations):  
(fixed) window average value of the input pulses.  
Average (Power):  
When applied to power values (watts, VARs, VA), the average is a calculated  
value that corresponds to the thermal average over a specified time interval. The  
interval is specified by the user in the meter profile. The interval is typically 15  
minutes. So, the Average Watts is the thermal average of watts over the  
previous 15-minute interval. The thermal average rises to 90% of the actual  
value in each time interval. For example, if a constant 100kW load is applied,  
the thermal average will indicate 90kW after one time interval, 99kW after two  
time intervals and 99.9kW after three time intervals.  
Bit:  
A unit of computer information equivalent to the result of a choice between two  
alternatives (Yes/No, On/Off, for example).  
Or, the physical representation of a bit by an electrical pulse whose presence or  
absence indicates data.  
Binary:  
Relating to a system of numbers having 2 as its base (digits 0 and 1).  
Block Window Avg:  
(Power)  
The Block (Fixed) Window Average is the average power calculated over a  
user-set time interval, typically 15 minutes. This calculated average corresponds  
to the demand calculations performed by most electric utilities in monitoring  
user power demand. (See Rolling Window Average.)  
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Byte:  
A group of 8 binary digits processed as a unit by a computer (or device) and  
used especially to represent an alphanumeric character.  
CBEMA Curve:  
A voltage quality curve established originally by the Computer Business  
Equipment Manufacturers Association. The CBEMA Curve defines voltage  
disturbances that could cause malfunction or damage in microprocessor devices.  
The curve is characterized by voltage magnitude and the duration which the  
voltage is outside of tolerance. (See ITIC Curve.)  
Channel:  
The storage of a single value in each interval in a load profile.  
CRC Field:  
Cyclic Redundancy Check Field (Modbus communication) is an error checksum  
calculation that enables a Slave device to determine if a request packet from a  
Master device has been corrupted during transmission. If the calculated value  
does not match the value in the request packet, the Slave ignores the request.  
CT (Current) Ratio:  
Demand:  
A Current Transformer Ratio is used to scale the value of the current from a  
secondary value up to the primary side of an instrument tranformer.  
The average value of power or a similar quantity over a specified period of  
time.  
Demand Interval:  
Display:  
A specified time over which demand is calculated.  
User-configurable visual indication of data in a meter.  
DNP 3.0:  
A robust, non-proprietary protocol based on existing open standards. DNP 3.0  
is used to operate between various systems in electric and other utility industries  
and SCADA networks. Nexus 1250 supports Level 1; Nexus 1252 supports  
Level 2.  
EEPROM:  
Nonvolatile memory. Electrically Erasable Programmable Read Only Memory  
that retains its data during a power outage without need for a battery. Also  
refers to meter’s FLASH memory.  
Energy Register:  
Ethernet:  
Programmable record that monitors any energy quantity. Example: Watthours,  
VARhours, VAhours.  
A type of LAN network connection that connects two or more devices on a  
common communications backbone. An Ethernet LAN consists of at least one  
hub device (the network backbone) with multiple devices connected to it in a  
star configuration. The most common versions of Ethernet in use are 10BaseT  
and 100BaseT as defined in IEE standards. However, several other versions of  
Ethernet are also available.  
Exception Response: Error Code (Modbus communication) transmitted in a packet from the Slave to  
the Master if the Slave has encountered an invalid command or other problem.  
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Flicker:  
Flicker is the sensation that is experienced by the human visual system when it  
is subjected to changes occurring in the illumination intensity of light sources.  
IEC 61000-4-15 and former IEC 868 describe the methods used to determine  
flicker severity.  
Form:  
Wiring and Hookup configuration for the Nexus 1260/1270.  
Harmonics:  
Measuring values of the fundamental current and voltage and percent of the  
fundamental.  
Heartbeat Pulse:  
Energy indicator on the face of the Nexus 1250/1252; pulses are generated per  
the programmed K value.  
e
Infrared Test Pulse:  
Energy indicator located on the upper left side of the face of the Nexus 1260  
/1270 meter; pulses are generated per the programmed K value.  
e
Integer:  
Any of the natural numbers, the negatives of those numbers or zero.  
Internal Modem:  
An optional modem within the meter’s enclosure that connects to the RJ-11  
telephone connector.  
Invalid Register:  
ITIC Curve:  
In the Nexus Modbus Map there are gaps between Registers. For example, the  
next Register after 08320 is 34817. Any unmapped Register stores no  
information and is said to be invalid.  
An updated version of the CBEMA Curve that reflects further study into the  
performance of microprocessor devices. The curve consists of a series of steps  
but still defines combinations of voltage magnitude and duration that will cause  
malfunction or damage.  
K :  
e
kWh per pulse; i.e. the energy.  
kWh:  
kilowatt hours; kW x demand interval in hours.  
KYZ Output:  
Output where the rate of changes between 1 and 0 reflects the magnitude of a  
metered quantity.  
LCD:  
Liquid Crystal Display.  
Light Emitting Diode.  
LED:  
Master Device:  
In Modbus communication, a Master Device initiates and controls all  
information transfer in the form of a Request Packet to a Slave Device. The  
Slave reponds to each request.  
Maximum Demand:  
The largest demand calculated during any interval over a billing period.  
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Modbus ASCII:  
Modbus RTU:  
Alternate version of the Modbus protocol that utilizes a different data transfer  
format. This version is not dependent upon strict timing, as is the RTU version.  
This is the best choice for telecommunications applications (via modems).  
The most common form of Modbus protocol. Modbus RTU is an open protocol  
spoken by many field devices to enable devices from multiple vendors to  
communicate in a common language. Data is transmitted in a timed binary  
format, providing increased throughput and therefore, increased performance.  
Network:  
NVRAM:  
A communications connection between two or more devices to enable those  
devices to send and receive data to one another. In most applications, the  
network will be either a serial type or a LAN type.  
Nonvolatile Random Access Memory is able to keep the stored values in  
memory even during the loss of circuit or control power. High speed NVRAM  
is used in the Nexus to gather measured information and to insure that no  
information is lost.  
Optical Port:  
Packet:  
A port that facilitates infrared communication with a (1260/1270) meter. Using  
an ANSI C12.13 Type II magnetic optical communications coupler and an  
RS-232 cable from the coupler to a PC, the meter can be programmed with  
Nexus Communicator software.  
A short fixed-length section of data that is transmitted as a unit. Example: a  
serial string of 8-bit bytes.  
Percent (%) THD:  
Protocol:  
Percent Total Harmonic Distortion. (See THD.)  
A language that will be spoken between two or more devices connected on a  
network.  
PT Ratio:  
Pulse:  
Potential Transformer Ratio used to scale the value of the voltage to the primary  
side of an instrument transformer. Also referred to as VT Ratio.  
The closing and opening of the circuit of a two-wire pulse system or the  
alternate closing and opening of one side and then the other of a three-wire  
system (which is equal to two pulses).  
Quadrant:  
Watt and VAR flow is typically represented usng an X-Y coordinate system.  
The four corners of the X-Y plane are referred to as quadrants. Most power  
applications label the right hand corner as the first quadrant and number the  
remaining quadrants in a counter-clockwise rotation. Following are the  
positions of the quadrants: 1st - upper right, 2nd - upper left, 3rd - lower left  
and 4th - lower right. Power flow is generally positive in quadrants 1 and 4.  
VAR flow is positive in quadrants 1 and 2. The most common load conditions  
are: Quadrant 1 - power flow positive, VAR flow positive, inductive load,  
lagging or positive power factor; Quadrant 2 - power flow negative, VAR flow  
positive, capacitive load, leading or negative power factor.  
(Programmable  
Values and Factors  
on the Nexus)  
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Register:  
An entry or record that stores a small amount of data.  
Register Rollover:  
Reset:  
A point at which a Register reaches its maximum value and rolls over to zero.  
Logs are cleared or new (or default) values are sent to counters or timers.  
Rolling Window  
Average (Power):  
The Rolling (Sliding) Window Average is the average power calculated over a  
user-set time interval that is derived from a specified number of sub-intervals,  
each of a specified time. For example, the average is calculated over a  
15-minute interval by calculating the sum of the average of three consecutive  
5-minute intervals. This demand calculation methodology has been adopted by  
several utilities to prevent customer manipulation of kW demand by simply  
spreading peak demand across two intervals.  
RS-232:  
A type of serial network connection that connects two devices to enable  
communication between devices. An RS-232 connection connects only two  
points. Distance between devices is typically limited to fairly short runs.  
Current standards recommend a maximum of 50 feet but some users have had  
success with runs up to 100 feet. Communications speed is typically in the  
range of 1200 bits per second to 57,600 bits per second. RS-232 connection  
can be accomplished using Port 1 of the Nexus 1250/1252 or the Optical Port  
on the face of the Nexus 1260/1270.  
RS-485:  
Sag:  
A type of serial network connection that connects two or more devices to enable  
communication between the devices. An RS-485 connection will allow  
multi-drop communication from one to many points. Distance between devices  
is typically limited to around 2,000 to 3,000 wire feet. Communications speed  
is typically in the range of 120 bits per second to 115,000 bits per second.  
A voltage quality event during which the RMS voltage is lower than normal for  
a period of time, typically from 1/2 cycle to 1 minute.  
Secondary Rated:  
Serial Port:  
Any Register or pulse output that does not use any CT or VT Ratio.  
The type of port used to directly interface with a PC.  
Slave Device:  
In Modbus communication, a Slave Device only receives a Request Packet from  
a Master Device and responds to the request. A Slave Device cannot initiate  
communication.  
Swell:  
THD:  
A voltage quality event during which the RMS voltage is higher than normal for  
a period of time, typically from 1/2 cycle to 1 minute.  
Total Harmonic Distortion is the combined effect of all harmonics measured in a  
voltage or current. The THD number is expressed as a percent of the  
fundamental. For example, a 3% THD indicates that the magnitude of all  
harmonic distortion measured equals 3% of the magnitude of the fundamental  
60Hz quantity.  
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Time Stamp:  
A stored representation of the time of an event. Time Stamp can include year,  
month, day, hour, minute and second and Daylight Savings Time indication.  
TOU:  
Time of Use.  
Voltage Imbalance:  
The ratio of the voltage on a phase to the average voltage on all phases.  
Voltage Quality Event: An instance of abnormal voltage on a phase. The events the meter will track  
include sags, swells, interruptions and imbalances.  
VT Ratio:  
The Voltage Transformer Ratio is used to scale the value of the voltage to the  
primary side of an instrument transformer. Also referred to as PT Ratio.  
Voltage, Vab:  
Voltage, Van:  
Vab, Vbc, Vca are all Phase-to-Phase voltage measurements. These voltages are  
measured between the three phase voltage inputs to the meter.  
Van, Vbn, Vcn are all Phase-to-Neutral voltages applied to the monitor. These  
voltages are measured between the phase voltage inputs and Vn input to the  
meter. Technologically, these voltages can be “measured” even when the meter  
is in a Delta configuration and there is no connection to the Vn input. However,  
in this configuration, these voltages have limited meaning and are typically not  
reported.  
Voltage, Vaux  
This is the fourth voltage input measured from between the Vaux and Vref  
inputs. This input can be scaled to any value. However, the actual input  
voltage to the meter should be of the same magnitude as the voltages applied to  
the Va, Vb and Vc terminals.  
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