Stunning Multi Wire Circuit

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

Multi wire circuit. Multi wire branch circuits a multi wire branch circuit in a residential dwelling contains two 120v wires of different phases a and b phase and share one neutral wire as return current. Our photo above left illustrates how a shared neutral circuit can be easily fouled up and made dangerous. Two separate wires are run along the track the contact wire for the locomotive and an electrically separate feeder wire.

Within this one cable there will typically be a black wire perhaps for the disposal and a red wire perhaps for the dishwasher. The neutral wire is being shared by the two. Wherever a multiwire branch circuit occurs various sections of the nec such as 225 33 b 230 71 b and 240 15 b permit two or three single pole switches or breakers on the multiwire branch circuits that are capable of individual operation one pole for each ungrounded conductor and one multipole disconnect provided these devices are equipped with identified handle ties or a master handle to disconnect all ungrounded conductors.

A common application of multiwire branch circuits as described in section 210 4 is for a 120 240 volt single phase system where three wires do the work of four the two ungrounded conductors sharing a single neutral in 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 each ungrounded conductor. In plain english a multiwire branch circuit or split wired receptacles means that two hot wires are sharing a neutral wire. However mishandling or improper wiring of multiwire branch circuits can cause overloading of the grounded neutral conductor and or the destruction of equipment.

Failure to properly terminate the ungrounded hot conductors. Multiwire branch circuits can be dangerous. Autotransformers along the track balance the loads between the contact and feeder wires reducing resistive losses.

It s true that multiwire branch circuits reduce raceway size voltage drop and the number of conductors. 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. Basically two hot wires are sharing a neutral wire.

A pretty common multi wire circuit would be to the dishwasher and garbage disposal. Each wire is fed with 25 kv with respect to ground with 50 kv between them. This wire will also have one white neutral wire and the bare ground wire.