What is a multi-wire branch circuit (MWBC) and what is required for it?

• A. A circuit where two hot conductors share a common neutral and require a circuit-breaker for each conductor to be tied.
• B. A circuit using two hot conductors with separate neutrals for each load.
• C. A system sharing a neutral between two ungrounded conductors; requires a common-trip or tied disconnect.
• D. A system with multiple neutrals sharing the same ground.

Answer: (C)

A multi-wire branch circuit uses two hot conductors sharing a single neutral. These two ungrounded conductors are typically on opposite phases of a 120/240V system, so the neutral carries only the difference in current between the two hots. This arrangement saves wiring space but requires a safety feature: all ungrounded conductors feeding the MWBC must be disconnected simultaneously. That means using a common-trip two-pole breaker or two single-pole breakers with a handle tie. This ensures you can’t have one hot energized while the other is off, which could leave the neutral or equipment energized in hazardous ways. If the two hots were on the same phase, the neutral could be overloaded because it would carry the sum of the currents, defeating the safety and purpose of the arrangement.