Simplified Guide To
Understanding
Short-Circuit Current Rating
FIND IT, FIX IT, FORGET IT
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Use this table to initiate the process of identifying the short-circuit current rating of your
components and devices in power circuits. For further information contact your local
Cooper Bussmann sales engineer, Cooper Bussmann Application Engineering,
Supply Disconnect and OCPD
200kA*
5kA
200kA*
10kA**
10kA
5kA
Feeder Circuit OCPD and Components
200kA*
5kA
200kA*
10kA**
10kA
200kA*
Branch Circuit OCPD and Components
200kA*
5kA
200kA*
10kA**
5kA***
5kA***
5kA
+
*Class CC, J, T, R, and L UL248 Branch Circuit Type Fuses.
**When used in conjunction with Class CC, J, T, R, and L UL248 Branch Circuit Type Fuses.
***50HP or less 480V
+Combination Rating is used for Sweep 1.
For Sweep 2 IR=5kA (Default Value)
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Glossary of Terms
Industrial Control Panel - An assembly of a
systematic and standard arrangement of two or more
components such as motor controllers, overload relays,
fused disconnect switches, fuses, and circuit breakers
and related control devices such as pushbutton
stations, selector switches, timers, switches, and
control relays with associated wiring, terminal blocks,
pilot lights and similar components.
Default
Value
Your
Value
Interrupting Rating - The highest current at rated
voltage that a device is intended to interrupt under
standard test conditions.
Short-Circuit Current Rating – The prospective
symmetrical fault current at a nominal voltage to which
an apparatus or system is able to be connected without
sustaining damage exceeding the defined acceptance
criteria
Control Circuit – A circuit that carries the electric
signals directing the performance of a controller, and
which does not carry the main power circuit. A control
circuit is, in most cases, limited to 15 amp.
10kA
5kA
Power Circuit – Conductors and components of
supply, branch, and feeder circuits, supplying main line
power to loads such as heaters, motors, lighting,
receptacles, power transformers, and appliances.
200kA*
5kA***
5kA***
5kA***
5kA***
10kA
2kA
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Find It, Fix It, Forget It
FIND IT – Look for... the Weakest Link
3. Buy more expensive components with
higher ratings — A 65kA circuit breaker will more
than double your cost compared to a 14kA circuit
breaker. The fusible solution provides an interrupting
rating as high as 200kA, at a comparable cost to your
existing design, making it the most economical solution.
The SCCR marking for the assembly will be based
upon the lowest short-circuit current or withstand rating
of any power circuit component contained within the
assembly — or the “weakest link”. Many components
used in industrial control panels, industrial machinery
and HVAC equipment may be the weakest link,
including:
• motor controllers
• definite purpose contactors
• supplemental protectors
• circuit breakers (with low interrupting ratings)
• power distribution blocks.
FORGET IT — Use Current-Limiting Fuses
Not only can modern current-limiting fusible solutions
fix undesired weak links and obtain a high assembly
short-circuit current rating, they can also provide
enhancements to your design in the areas of flexibility
of installation, increased workplace safety, and reliable
protection through the life of your equipment. These
enhancements take care of the hassle associated with
equipment with limited ratings so you can FORGET IT!
FIX IT — How To Get A Higher SCCR So
Equipment Isn’t Limited
Benefits of Using Cooper Bussmann Current-
Limiting Fuses
Straight Voltage Ratings:
• Straight voltage ratings allow for more installations where
equipment can be installed. Straight voltage rated
equipment can be installed in any type of electrical system.
With a straight voltage rating you can ship it anywhere and
not have to worry.
By fixing these weakest links, higher SCCRs can be
achieved. In general, there are three options:
1. Use overcurrent protective devices with
higher interrupting ratings — Overcurrent
protective devices with low interrupting ratings often
become the weakest link and limit the SCCR of the
assembly. The interrupting ratings of the overcurrent
protective devices used directly affects the assembly
rating. The only fix is to use devices with higher
interrupting ratings.
High Assembly SCCRs:
• High SCCRs allow for more applications where equipment
can be installed. With a high SCCR you can ship it
anywhere and not have to worry.
Circuit Breaker &
Motor Starter
Combination
Fuse & Motor Starter
Combination
• Fusible disconnect with
Cooper Bussmann LP-CC
fuses marked interrupting
rating 200kA
• Three-pole circuit
breaker marked
• A wider range of fault current levels provides assurance that
the equipment will be installed correctly and safely.
• Meets the UL508A and NEC® requirements for SCCR
marking.
interrupting rating 14kA
• Motor starter marked
50kA when protected by
fuses or circuit breakers
• Motor starter marked 50kA
when protected by fuses or
circuit breakers
• The SCCR is 50kA
• The SCCR is 14kA
• Marketing advantage over competitive equipment with a
lower rating.
2. Use current limitation to fix low rated
components — It only takes one component with a
low SCCR to limit the entire assembly. Many of the
components used in industrial control applications have
low short-circuit current ratings. Fix these low rated
components and the assembly rating by using
current limitation. Since current-limiting fuses reduce high
level short-circuit currents to a minimal level, they allow
the use of these lower rated devices while
Increased Flexibility In Panel Use and Installation:
• Valuable time that was spent gathering information for
proper application is drastically reduced with fuses because
modern current-limiting fuses can provide high assembly
SCCRs and straight voltage ratings since they have:
- High Interrupting Ratings of 200,000A or more
- Excellent current limitation to protect low rated
components at high short-circuit current levels
providing a higher SCCR.
- Straight voltage ratings so they can be installed in any
type of application independent of the grounding scheme
used, unlike devices with a slash voltage rating which are
limited to installation in ONLY a solidly grounded wye
type system
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Cooper Bussmann Products And
Technical Support Delivered Worldwide
Customer Assistance
Customer Satisfaction Team
Application Engineering
Application Engineering assistance is available to all
customers. The Application Engineering team is staffed
by degreed electrical engineers and available by phone
with technical and application support Monday – Friday,
8:00 a.m. – 5:00 p.m. Central Time.
The Cooper Bussmann Customer Satisfaction Team is
available to answer questions regarding Cooper
Bussmann products and services. Calls should be made
between 8:00 a.m. – 4:30 p.m. Central Time
for all US time zones.
The Customer Satisfaction Team can be reached via:
• Phone: 636-527-3877
• Toll-free fax: 800-544-2570
• E-mail: [email protected]
Application Engineering can be reached via phone, fax
or email:
• Phone: 636-527-1270
• Fax: 636-527-1607
• E-mail: [email protected]
Emergency and After-Hours Orders
To accommodate time-critical needs, Cooper Bussmann
offers emergency and after-hours service for next flight
out or will call. Customers pay only standard price for
the circuit protection device, rush freight charges and a
modest emergency fee for this service. Emergency and
after-hours orders should be placed through the
Customer Satisfaction Team. Call:
Online Resources
services:
• Product cross reference
• Arc-flash calculator
• SCCR calculator
• Training modules
• 8:00 a.m. – 4:30 p.m. Central Time 636-527-3877
• After hours 314-995-1342
Your Authorized Cooper Bussmann Distributor is:
©2005 Cooper Bussmann • St. Louis, MO 63178
636-394-2877 • www.cooperbussmann.com
Reorder #7009 11-05-5M
Printed in USA
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