what is SCCR if it doesn't prevent arc flash?

One of the government agencies I worked for decades ago was one of the few in the State that addressed SCCR ratings. It was commonplace for equipment suppliers (and sometimes manufacturers) to have the "deer in a headlight" look when rejections were issued. Normally we had to move a few steps up the chain before we heard "Oh! You are one of THOSE" and then it would be addressed.
(The same scenario often applied to our requiring NRTL listings)
 
don_resqcapt19 said:
However, you will have to find some way to limit the fault current on the line side of the 20 amp breaker that feeds these loads. Unlikely you will find one suitable for use with that high AIC.
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To add a little to this, if you have 100kA available how often do you have (or desire to have) 15 and 20 amp circuits connected to the equipment that has that much available? Often that is main distribution type equipment and only supplies feeders or if there is branch circuits they are some large capacity load. Usually your general use branch circuits are on some some feeder or even have a transformer in the path and the fault current at the origin of those branch circuits is likely below 10kA or at least has series rated components involved. At very least a 22-25 kA main breaker in that branch panel that is series rated for use with the 10kA branch breakers, which that combination will be covered even by most commonly used "load centers" you find in residential installs.
 
malachi constant said:
So all motors [technically motor controllers, but I'm going to be loose with my language and say "motors"], all motors everywhere, always, should have their available fault current calculated and compared against the controller's SCCR?
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Loose with the language is not serving you here. It is NOT about the motor, it is about the EQUIPMENT ahead of it. All electrical devices that control the flow of POWER (as opposed to control circuits) must be capable of surviving a short circuit event without entering into a “RUDE” condition (Rapid Unplanned Disassembly Event). That applies to breakers, disconnect switches, fuses and fuse holders, terminals, contactors, overload relays, solid state power devices, EVERYTHING in the power circuit, EXCEPT the motor or load device (heater) itself. Fuses and circuit breakers already have that baked into their “interrupt ratings), commonly shown as “AIC”, and fuse holders generally are rated for the fuses they can hold. But the rest of it must be tested and listed with the breakers or fuses based on the “let-through” energy they allow before clearing the fault.

SCCR is not something that we can do in the field, the equipment must STATE it now. If there is nothing done, you can assume an untested “courtesy” level of 5kA. In most older RESIDENTIAL applications breakers are rated 10kAIC, because it’s hard for a residential service transformer to allow that much fault current to go though it. So 5kA SCCR might be OK too by the time you factor in the wire impedance out to where the equipment pad is. But it’s not guaranteed, and an AHJ might demand to see calculations showing that something with a 5kA SCCR label has that little AFC at the terminals. But if you get a 5kA SCCR label on a piece of commercial or industrial equipment, it can be next to impossible to connect it.
 
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