Cooper Bussmann Electronics Short-Circuit Current Rating manual Find It, Fix It, Forget It

Find It, Fix It, Forget It

FIND IT – Look for... the Weakest Link

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.

FIX IT — How To Get A Higher SCCR So Equipment Isn’t Limited

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.

Circuit Breaker &	Fuse & Motor Starter
Motor Starter	Combination
Combination	• Fusible disconnect with
• Three-pole circuit	Cooper Bussmann LP-CC
	fuses marked interrupting
breaker marked
	rating 200kA
interrupting rating 14kA
• Motor starter marked	• Motor starter marked 50kA
	when protected by fuses or
50kA when protected by
	circuit breakers
fuses or circuit breakers
• The SCCR is 14kA	• The SCCR is 50kA

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

providing a higher SCCR.

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.

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!

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.

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.

•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.

•Marketing advantage over competitive equipment with a lower rating.

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

-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