An MWBC, multiwire branch circuit, uses two or three ungrounded conductors on different phases with one shared neutral, such as 12-3 cable feeding two kitchen circuits. The neutral carries only the imbalance between the phases, which saves copper, but losing that neutral puts loads in series across 240 V and burns out equipment. Code requires the hots on a two-pole or handle-tied breaker so they shut off together, and the neutral pigtailed rather than fed through devices.
Kitchen's an MWBC on 12-3, so use a two-pole breaker and make sure those hots land on opposite phases.
Putting both hots of an MWBC on the same phase doubles the current on the shared neutral with no breaker to stop it, a hidden fire hazard.
Also heard as
- multiwire branch circuit
- Edison circuit
- shared-neutral circuit
Related terms
Pigtail
Short length of wire spliced to several conductors so only one lead goes to a device terminal.
Hot
Ungrounded, voltage-carrying conductor of a circuit, and as an adjective anything that is live.
Get bit
To take an electric shock on the job, as in got bit by a hot neutral.
Romex
Brand name used for nonmetallic sheathed cable, the plastic-jacketed cable that wires most North American houses.