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Thread: Equipment Grounding Conductor Required for 24 VDC System?

  1. #11
    Join Date
    Sep 2015
    Location
    Iowa
    Posts
    37
    This is interesting discussion. I'm really surprised there's not a straight easy answer for it. I don't know either where in the code but I've never seen an EGC routed with such circuits. You're on the right track with 250.112 although I don't understand the 2-wire cord stipulation.
    "They said it couldn't be done, but the fool didn't know it..."

  2. #12
    Join Date
    Feb 2004
    Location
    Shelby Twp. MI, near Detroit
    Posts
    342
    Speaking of interesting. This subject actually attracted the attention of Mr. Holt himself. In a private discussion, he helped me see that the NEC does not require this 24 Volt system be grounded and therefore would not require an EGC for any part of the circuit. This then lead to the next twist, and that was when UL 508A is involved (in that the 24 volt source in my case is from a UL 508A Industrial Control Panel) UL 508A requires the 24 volt secondary of the power supply to be grounded only when the primary source is greater than 150 volts to ground (there are power supplies fed with 480 V 3 phase in some cases) or where the primary supply is ungrounded at any voltage. Nowhere is grounding of the secondary prohibited. The fact that the secondary is grounded (whether required or not required) does not in and of itself mean that the circuits need to provide an EGC. So in conclusion, in my case, there is no need to provide an EGC along with the 24 volt circuits supplying power to field devices like I/O blocks, operator interfaces, Ethernet communication devices built into VFDs.

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