Power or Control Circuit UL 508A

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BN32

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If one of my 480VAC branches in my panel is feeding a 3PH 40A 24VDC power supply that powers some stepper motors, is that considered a part of my power circuit? And would I need to include the load side of my power supply in my SCCR calculation?

Typically I'd stop at the branch circuit protective device of power supply but I wasn't sure if that changes with the presence or 24VDC stepper motors.
 
No. The output of the power conversion device is irrelevant to the SCCR of the panel.

The power supply itself will be included though, so make sure it has a listing and if that listing requires specific fuses, make sure you use them, otherwise it will degrade your SCCR for the entire panel to 5kA, which is all but useless.
 
Jraef said:
The power supply itself will be included though, so make sure it has a listing and if that listing requires specific fuses, make sure you use them, otherwise it will degrade your SCCR for the entire panel to 5kA, which is all but useless.
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If the wiring to that power supply is fed by (typically 16AWG) wiring of sufficient length to limit fault current at the supply terminals to 5kA, would that eliminate the lowering of the panel rating? I've had several contractors consider that to be true.
 
No, that’s not part of the process of determining SCCR, someone is making that up. I suppose maybe they are thinking that the wire size will act like a current limiting fuse wire(?), but that’s not a legitimate consideration.

UL508A Supplement SB outlines the entire process of determining the SCCR of a panel. There is a fairly basic process that anyone can do, it’s not “rocket surgery”…
 
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