What must be done to multi-wire branch circuits that share a neutral?

Multi-wire branch circuits that share a neutral must have a double-pole circuit breaker to ensure safety and proper operation. This requirement stems from the fact that a multi-wire branch circuit typically consists of two or more hot conductors that share a common neutral conductor. When using a single-pole breaker for one of the hot conductors, it allows that circuit to be disconnected while the other remains powered. This can lead to a situation where the neutral still carries current from both circuits, possibly creating an overload or a hazardous condition.

A double-pole circuit breaker simultaneously disconnects both hot conductors, ensuring that when either circuit needs to be shut off, the shared neutral is not carrying any load. This arrangement helps to maintain balance across the circuits and prevents overloading of the neutral, significantly reducing the risk of overheating and potential fire hazards.

Other options do not ensure the required disconnection of both hot wires simultaneously, which is why they do not meet the safety standards necessary for circuits sharing a neutral.