409.110, UL508, and 120VAC only

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wolfsburged

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Trying to clarify whether I am required to calculate and mark a cabinet with SCCR in this situation:

Panel will be fed 120VAC 1PH 40A which is then split to DC power supplies (protected via UL 489 circuit breakers) and a GFCI outlet with integral breaker (convenience port).

The incoming feed is being passed through a fused disconnect with class J fuses at 40A. The disconnect is rated 200kA SCCR, and the fuse is 300kA.

Each breaker that is between the disconnect and the power supplies are 6A, and there are multiple of these. Each has SCCR of 10kA.

The GFCI outlet is not listed with an SCCR, so I am assuming 5kA here.

Now the exception is: "Exception to (4): Short-circuit current rating markings are not required for industrial control panels containing only control circuit components."

Now various places I have seen control circuits defined as limited to 15 amps "in most cases."

The only thing leaving this panel is 24VDC. No motors (except for a cabinet fan). No heaters. No 120VAC circuits leaving the panel.

Does this fall under the exception as being control circuits only (no single breaker larger than 6A however overall feed is 40A)?

If it does not fall under the exception, then my limiting factor would be the 5kA breaker. However I should be able to use the Class J current limiting fuse to increase the protection, but am unsure of how to calculate the increased rating in 120VAC, not 3PH.
 
wolfsburged said:
Trying to clarify whether I am required to calculate and mark a cabinet with SCCR in this situation:

Panel will be fed 120VAC 1PH 40A which is then split to DC power supplies (protected via UL 489 circuit breakers) and a GFCI outlet with integral breaker (convenience port).

The incoming feed is being passed through a fused disconnect with class J fuses at 40A. The disconnect is rated 200kA SCCR, and the fuse is 300kA.

Each breaker that is between the disconnect and the power supplies are 6A, and there are multiple of these. Each has SCCR of 10kA.

The GFCI outlet is not listed with an SCCR, so I am assuming 5kA here.

Now the exception is: "Exception to (4): Short-circuit current rating markings are not required for industrial control panels containing only control circuit components."

Now various places I have seen control circuits defined as limited to 15 amps "in most cases."

The only thing leaving this panel is 24VDC. No motors (except for a cabinet fan). No heaters. No 120VAC circuits leaving the panel.

Does this fall under the exception as being control circuits only (no single breaker larger than 6A however overall feed is 40A)?

If it does not fall under the exception, then my limiting factor would be the 5kA breaker. However I should be able to use the Class J current limiting fuse to increase the protection, but am unsure of how to calculate the increased rating in 120VAC, not 3PH.
Click to expand...

What is SCCR?

Welcome to the forum.....:thumbsup:
 
wolfsburged said:
Trying to clarify whether I am required to calculate and mark a cabinet with SCCR in this situation: ....
Click to expand...

Disclaimer: Four one-off panels, one place, one time, one AHJ rep opinion - not exactly a universal fits-all solution

I've built a couple of Industrial Control panels per NEC 409. The AHJ rep here wanted the panel label exactly as specified in 409.110. If there was as little as a single 120VAC, 15A power source, he wanted to see a calculated SCCR. And he also asked for a calculaton for available short circuit current at the installed location (409.22)

Side note: Seemed reasonable to me. If we had the panels built at a NRTL panel shop, it would have the SCCR on the nameplate.

I used UL 508A, supplement SB for the SCCR, and the Bussmann Point-to-Point paper for the ASSC. Bussmann also has a paper on calculating SCCR.

ice
 
UL508a supplement SB says that only power circuits have a SCCR.

Therefore you could not possibly use that supplement to calculate a SCCR for a control circuit.
 
Have you checked the manufacturer listing as the the rating of the breaker with the class J fuse is the circuit (series rating) ?
Being a 40 AMP circuit, in most cases the SCA at the end of the supply circuit would be quiet low. Has this been investigated ?
 
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