Understanding where SCCR markings are required.

[Abraham V]

I'm looking for clarity on which pieces of electrical equipment are required to have SCCR included on nameplates. Can anyone provide insight on that?

As far as I know, the 2023 NEC discusses SCCR in only the following locations: 110.10, 409.22, 409.110, 440.4(B), 670.3(A)(4). Is it reasonable to understand that SCCR markings are only required on industrial control panels? Are there requirements to know SCCR for some equipment (even if it isn't marked with the rating) so that one can show that the AFC doesn't exceed the SCCR?

 

[mayanees]

It shows up in over 50 locations in the 2023 NEC, as I searched "short circuit current rating" in NFPA Link, including 371.40, 242.8, 408.6, 646.7, 670.5, 440.10, 620.16, 409.22, 430.83(F), 646.7(A) & (B)...etc. which covers a whole bunch of equipment.

 

[kwired]

There is two things to consider here.

1. Interrupting rating. This applies to almost anything that is intended to open/close a circuit that may have potential to have to carry fault level current when it operates.

2. Withstand rating. This applies to items that will carry the fault current but do not need to open/close the circuit. They still need to be able to withstand magnetic forces imposed on them by a fault, so securing of components is somewhat of a factor in withstand rating or simply overall ability to withstand heating that may occur during the fault.

 

[petersonra]

I don't think the code requires some kind of sccr marking except in a few specific cases. The ul listing for many products does though, although the marking is not always on the device itself.

 

[Jraef]

I agree with what kwired said, except the term "withstand rating" no longer exists in the NEC (it used to). That is essentially what "SCCR" has supplanted, I think because withstand rating was not clearly defined.

I look at it this way: IF the equipment already has an Interrupt Capacity rating, a.k.a. "AIC", the "SCCR" is implied anyway. So if you have a panelboard, switchboard or fused disconnect that is ALREADY listed for 65kA, it is implied in that rating that rating that the GEAR itself can withstand that much fault current. So you don't see SCCR applied to those pieces of equipment, it would be redundant.

The addition of the "SCCR" nomenclature was to clarify that in the case of OTHER equipment that had electrical power devices inside, the IC rating of the main protective device alone is not enough; the entire power circuit must be evaluated. So just because you use a Main breaker that is rated for 35kAIC, that does NOT mean that every device below it is capable of withstanding the mechanical forces that will be exerted on them during a 35kA short circuit, while that breaker is acting to take it off line. Someone must evaluate that using a recognized process, such as described in UL-508A Supplement SB, which applies to "industrial control panels". That does not however preclude someone from using the same process for something that is NOT an industrial control panel.

 

[Abraham V]

It shows up in over 50 locations in the 2023 NEC, as I searched "short circuit current rating" in NFPA Link, including 371.40, 242.8, 408.6, 646.7, 670.5, 440.10, 620.16, 409.22, 430.83(F), 646.7(A) & (B)...etc. which covers a whole bunch of equipment.

Thanks for this. I hadn't heard of NFPA link before. That's very helpful.

 

[mayanees]

Thanks for this. I hadn't heard of NFPA link before. That's very helpful.

Sure Abraham, and you can get free access by registering with your email address at NFPA.org. Granted the "free access" package is limited in capability as I think you can only read from it, but NFPA Link gives you access to all of the other NFPA Standards as well. We generally use 70 (NEC), 70B (Electrical Equipment Maintenance) and 70E (Standard for Electrical Safety) but there are so many more out there.

 

[kwired]

I agree with what kwired said, except the term "withstand rating" no longer exists in the NEC (it used to). That is essentially what "SCCR" has supplanted, I think because withstand rating was not clearly defined.

I look at it this way: IF the equipment already has an Interrupt Capacity rating, a.k.a. "AIC", the "SCCR" is implied anyway. So if you have a panelboard, switchboard or fused disconnect that is ALREADY listed for 65kA, it is implied in that rating that rating that the GEAR itself can withstand that much fault current. So you don't see SCCR applied to those pieces of equipment, it would be redundant.

The addition of the "SCCR" nomenclature was to clarify that in the case of OTHER equipment that had electrical power devices inside, the IC rating of the main protective device alone is not enough; the entire power circuit must be evaluated. So just because you use a Main breaker that is rated for 35kAIC, that does NOT mean that every device below it is capable of withstanding the mechanical forces that will be exerted on them during a 35kA short circuit, while that breaker is acting to take it off line. Someone must evaluate that using a recognized process, such as described in UL-508A Supplement SB, which applies to "industrial control panels". That does not however preclude someone from using the same process for something that is NOT an industrial control panel.

You are correct that NEC no longer uses "withstand rating". But that basically is what SCCR means though they use a little more descriptive definition in art 100 because apparently some couldn't understand the somewhat self defining "withstand rating"

a bigger problem regardless of the term or definition is people not learning terms and definitions. Take all the terms with the root word "ground" in them. Many kind of lump them all together meaning wise even though they all have a specific definition.