Multi Wire Branch Circuit Diagram

When a three wire nm cable is used for this type of circuit.

Multi wire branch circuit diagram. The black wire is usually the a phase 120 v. Each of these circuits is typically a 15 amp circuit. A single phase 3 wire 120240 v circuit supplies a 1275 w 120 v hair dryer and a 600 w 120v television. According to nec article 100 a multiwire branch circuit consists of two or more ungrounded conductors that have a voltage between them and a grounded conductor that has equal voltage between it and each ungrounded conductor of the circuit and that is connected to the neutral or grounded conductor of the system.

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. Other common uses are for lighting circuits for the two small appliance branch circuits required at the kitchen counters and for home runs back to a panel. A common application of multiwire branch circuits as described in section 2104 is for a 120240 volt single phase system where three wires do the work of four the two ungrounded conductors sharing a single neutralin a 20 amp multiwire branch circuit if the two ungrounded conductors each carry 15 amps some people think the neutral carries 30 amps or the combined total of the current on. By requiring each multi wire branch circuit to be provided with a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates such as at the panelboard or load center a change to 2104b in the 2008 nec prompted the industry to move away from multiwire branch circuits.

For 15 amp circuits we usually run 14 3 with ground red black white 14 wires plus the ground wire. If the grounded neutral conductor is interrupted it will cause the 120 v television to operate at 163 v and consume 1110 w of power instead of 600 w for only a few seconds before it burns up. A multiwire branch circuit in the electrical code is defined as a branch circuit that consists of two or more ungrounded conductors two or more hot wires that have a voltage between them they are not on the same electrical phase and so are connected to different buses in the electrical panel and a grounded conductor the neutral wire that has equal voltage between it and each ungrounded conductor hot wire of the circuit and that is connected to the neutral or grounded conductor. A multi wire circuit that shares the same neutral must have each of the two circuits on separate buses and the circuit breakers must be have their handles tied.

The most common multi wire branch circuit is for the dishwasher and disposal circuits. This will ensure a balanced load on the neutral. Lets keep using the example of the dishwasherdisposal multi wire circuit.