Multiwire Branch Circuit (MWBC)

Category: infrastructure

A circuit configuration sharing a single neutral conductor among multiple distinct ungrounded hot phases.

MWBCs save raw copper material costs by allowing two or three hot legs to balance their return currents along a single common neutral line. Because a mistake can overload the neutral wire or send 240V into 120V devices, the NEC requires a mandatory handle-tie on the breakers to open all phases simultaneously.

Common Examples

• The inspector flagged the multiwire branch circuit because it lacked the required dual-pole simultaneous handle-tie breaker link.
• In an MWBC configuration, the common neutral line must never be broken or split while the underlying circuit paths are actively energized.