Multiwire Branch Circuit - Electrical 101
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Multi-Wire Branch Circuits

A multi-wire branch circuit in a residential dwelling contains two 120 V wires of different phases (A and B phase) and share one neutral wire as return current. When a three wire NM cable is used for this type of circuit:

See example diagrams below. Receptacle ground connection diagram shown separately.

Multi-Wire Branch Circuit Wiring Diagrams

Multi-Wire Branch Circuit Correct Wiring Diagram

Multi-wire Branch Circuit Correct Wiring DiagramMulti-wire Branch Circuit Preferred Wiring Diagram

The neutral wires are connected together before connecting to the terminals on the left receptacle. The NEC does not require the line (black) wires to be connected together before connecting to the terminals on the left receptacle.

It is preferred that the line (black) wires to be connected together before connecting to the terminals on the left receptacle, even though it is not required by the NEC.

Multi-Wire Branch Circuit Incorrect Wiring

Multi-wire Branch Circuit Incorrect Wiring

The neutral wires are not connected together before connecting to receptacle on left. The two left receptacles do not meet the NEC for a multi-wire branch circuit. If the neutral wires are disconnected with B phase power turned on, the neutral wire from the B phase receptacle is line voltage.


Multi-Wire Branch Circuit Preferred Wiring Diagram

Basic Electricity

Electrical Voltages

Low Voltage

Electrical Definitions

Ohm’s Law

Electrical Circuits

Multi-Wire Branch Circuits

Circuit Current Ratings

NM Cable (Romex®)

Wire Connectors