Simplified Guide To Understanding Short-Circuit Current …

Simplified Guide ToUnderstandingShort- circuit Current RatingFIND IT, FIX IT, FORGET ITWhat Is A Short-Circuit Current Rating(SCCR)?SCCRs on components and equipment represent themaximum level of Short-Circuit Current that the component or equipment can withstand and is used fordetermining compliance with NEC This ratingcan be marked on individual components or assemblies. The new SCCRs represent the maximumamount of fault Current that the assemblycan withstandunder fault conditions. Assembly ratings take intoaccount all components contained within the equipmentrather than just the main overcurrent protective common mistake is to assume that the interruptingrating of the overcurrent protective device protectingthe circuit represents the SCCR for the entire ratings, used for compliance with NEC , apply solely to the overcurrent protective is the characteristics of the overcurrent protectivedevice ( opening time, let-through energy) thatneed to be used in determining compliance with NEC , not the interrupting Is Affected By The SCCR MarkingsThe 2005 NEC has requirements for anyone buildingequipment listed to the 2005 NEC or to UL508A andrequires the following to be marked with an SCCR: Industrial Control Panels [ ] Industrial Machinery Electrical Panels [ (A)] Certain HVAC Equipment [ (B)] Meter Disconnect Switches [ (3)] Certain Motor Controllers [ ]Effective April, 2006, all equipment list

• 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

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