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Monday, November 28, 2016
Question:
Installed condition: Outdoor Sewage lift station with a non separately derived permanently installed 30 kw generator and automatic transfer switch for complete site backup. \Utility service disconnecting(100 amp) mounted on a pole in close proximity. Generator has over current / disconnecting means factory installed in its enclosure. Grounding electrode conductor properly installed to the service disconnecting means with wire type equipment grounding conductors installed with a all feeders and branch circuit and connected to ground bars at various equipment.
Question: The inspector wants us to extend the grounding electrode conductor at the service disconnect and connect to the frame of transfer switch and generator. Does the NEC require this extension of the grounding electrode conductor when all items are already bonded by a wire type equipment grounding conductor that ultimately is tied to the grounding electrode conductor at the service disconnecting means?
Thank you, Don Van Duyn
A
Answer:
Hey Don thanks for your question. The NEC does not require a generator frame to be connected to a grounding electrode conductor but the generator manufacturer's instructions might. If the service grounded conductor is directly connected to the generator grounded conductor then the generator is not a Separately Derived System, as defined in Article 100 - which is what you stated. The grounded conductor at the generator is not allowed to be reconnected to ground as stated in 250.24(A)(5), it is already grounded at the service. An auxiliary grounding electrode is allowed as stated in 250.54.
EXHIBIT 250.12 for 250.30 in the 2014 NFPA NEC Handbook is a good illustration of what I understand your installation to be and shows the grounding electrode conductor, only at the service.