National Electrical Installation Standards

Standards as High as Your Own

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Wednesday, December 11, 2019

Question:

Re: CQD answer published Wednesday, December 4, 2019 - Service Point

I do not agree. If the transformer primary is supplied by the utility then the transformer is the service point. A grounded conductor would be required to the service disconnect.

Thanks

Mike Bressler
A

Answer:

Hey Mike thanks for your comment. It's not clear what you mean by "the transformer is the service point". The Service Point is defined in Article 100 and as explained in the Informational Note is the demarcation point, typically where ownership changes. If the customer owns the transformer then the secondary conductors are feeders and the service point is on the primary side. An illustration that is similar to what is described in the question is in the 2017 NFPA NEC Handbook as Exhibit 230.28 on page 144. You are correct that if the utility system supplying the service is grounded then a grounded conductor must be installed as stated in 250.186 but this is on the primary of the transformer. The transformer secondary needs to be installed based on the rules in 250.30 and a grounded conductor is not required but a supply side bonding jumper is.

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