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I work at a university with a large number of buildings constructed using multi-wire branch circuits before multi-pole breakers were required. During remodels, we sometimes need to add one receptacle that could be easily be connected to an existing multi-wire branch circuit. We now do not allow extensions of these circuits and install a new circuit with an individual neutral. I was asked to provide code sections that would not allow a new receptacle from being added to an existing multi-wire branch circuit. I have not been able to find a requirement that justifies our approach.
1. Article 210.4 describes requirements for multi-wire branch circuits. Mainly, individual branch circuits with a common grounded conductor (neutral) shall have be fed from a multi-pole breaker and the conductors identified in the panel.
2. Section 406.4 has general installation requirements for receptacle outlets. Section 406.4(D) (3) requires replacements to be GFCI if the location is required to be GFCI elsewhere in the Code. Section 406.4(D) (4) requires replacements to be AFCI if the location is required to be AFCI elsewhere in the Code.
3. I did not find anything in Article 406 that would prevent existing receptacles on multi-wire branch circuits from being replaced without bringing the existing circuit up to compliance with 210.4.
4. I do not find anything that would prevent extending one of the branch circuits of a multi-wire branch circuit to a new receptacle without bringing the existing circuit up to compliance with 210.4.
Is there a requirement elsewhere in the NEC that would not allow an extension of an existing multi-wire branch circuit to a new receptacle without bring the existing multi-wire branch circuit up to compliance with the latest Code?
Hey Rodney thanks for your question. You are correct there is no clear language that requires providing a simultaneously disconnecting means for extensions of multi-wire branch circuits in 210.4 or for replacements of receptacles in 406.4(D). Interestingly there are requirements for AFCI protection, if branch circuit extensions or modifications are made in, 210.12(D) but not for GFCI protection in 210.8, possibly because of the different types of AFCI products. Some could argue that the extension is a new portion of a branch circuit but it is a stretch given the other specific rules.
With all of that the reason simultaneous disconnecting is required for multi-wire branch circuits is safety. You have an opportunity to do that when extensions, modifications or replacements are made, possibly by just adding an identified handle tie to the circuit breakers, even though there is not clear language to require it.
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