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Wednesday, July 28, 2021

Question:

Greetings CQD,

I often see multi-sectional modular buildings with the service mounted on a unistrut structure. From the service, a feeder is installed to each section (panel) of the modular. Is this not a violation of NEC 225.30 for Number of supplies? Also at each sub panel, should there be a ground system for each building section/panel due to NEC 250.32(A)?

Thanks

Lee Watson

A

Answer:

Hi Lee,

Thanks for participating. We've read your question. If multiple modular buildings are connected together to form one, then the service can supply the separate panelboards (with separate feeders) within each modular unit of the group. This is a common application especially for temporary offices on construction sites. Section 250.30(B) now contains allowances for more than one feeder per building or structure served. The grounding electrode requirements in 250.32(A) would be applicable but only for the entire combination of modulars connected together, rather than grounding electrode system for each separate panelboard. You might be wise to inquire with the local authority having jurisdiction to confirm how that will apply Part II of Article 225 to this situation. 

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