National Electrical Installation Standards

Standards as High as Your Own

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Thursday, January 18, 2018

Question:

Re: CQD answer published Wednesday, January 10, 2018 -Multiwire Branch Circuit

Thanks to all of the numerous readers that sent in comments regarding the question about circuit breakers in position 32 and 36 using a "shared" neutral.

A

Answer:

You are correct and thanks for pointing that out. A simultaneous means of disconnecting all of the ungrounded conductors is required as stated 210.4(B) which the answer pointed out. But the ungrounded conductors must be supplied from different phases to be a multiwire branch circuit as stated in the definition of Branch Circuit, Multiwire in Article 100. There must be a voltage between the ungrounded conductors or the neutral current would be the total of both ungrounded conductors in a single-phase system which is likely the case in the example provided. So besides the circuit breakers having to be next to each other so that a simultaneous means of disconnect can be provided they need to be next to each other so that the grounded conductor (neutral in this case) is not overloaded.

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