Multiwire branch circuits and shared neutrals
A multiwire branch circuit shares one neutral among its hot conductors. The code requires the hots to be disconnected together where the circuit starts, the conductors to be grouped, and the circuit to serve only line-to-neutral loads, with limited exceptions.
What the code requires
210.4(A): Multiwire branch circuits, where hot conductors share a neutral, are permitted and may be treated as multiple circuits. Except where 300.3(B)(4) allows otherwise, all of the circuit's conductors must start at the same equipment that contains the branch-circuit breakers or fuses.
210.4(B): Each multiwire branch circuit needs a means to disconnect all of its hot conductors at the same time, at the point where the circuit originates. Single-pole breakers with handle ties identified for the purpose, or a breaker with a common internal trip, can serve this purpose (see 240.15(B)).
210.4(C): A multiwire branch circuit may supply only line-to-neutral loads, except as noted below. 210.4(D): The hot and neutral conductors of each multiwire branch circuit must be grouped together, for example with cable ties, as 200.4(B) requires.
On the job
- Two single-pole breakers on a shared-neutral circuit without an identified handle tie fail inspection.
- An ungrouped multiwire neutral in a panel fails the grouping rule. If both hots are landed on the same bus phase, the shared neutral can be overloaded.
Exceptions that matter
- A multiwire branch circuit may supply line-to-line loads if it serves only one piece of utilization equipment.
- Line-to-line loads are also allowed where the branch-circuit breaker or fuse opens all hot conductors at the same time.
- Grouping is not required where a raceway or cable is unique to that circuit, or where the conductors pass through a box without a splice.
Related sections
- NEC 200.4(B)
- NEC 240.15(B)
- NEC 300.3(B)
- NEC 300.13(B)
- NEC 210.5
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