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Monday, October 11, 2021
Question:
Hello Code Question of the Day.
I have a project that includes a generator for an emergency system. Do I have to ground the generator as a separately derived system? I can't seem to locate direction in the NEC on this issue.
Thanks for any help you can provide.
Jim McDonald
A
Answer:
Hi Jim,
Thanks for the question. The NEC does provide direction on this, but it could be more specific and probably should be in a requirement rather than an Informational Note. See Informational Note No. 1 to Section 250.30 which indicates that an alternate ac power source, such as an on-site generator, is not a separately derived system if the grounded conductor is solidly interconnected to a service supplied system grounded conductor. An example of such a situation is where alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served. So the key to making the system grounding determination is directly related to the transfer switch equipment. Hope this is useful.