Branch Circuits

[Reesh14]

I had a quick question about branch circuit wiring. I have a 277V, single phase motor to power from a 277/480V electrical panel. I just want to make sure that I should use 2 #12 AWG + 1#12 AWG Gnd. in 3/4" in Conduit. I mainly want to know whether it should be 2 or 3 #12 Awg non-ground conductors. I know for 120/1ph 2 wires are used and 3 wires are used for 3 phase. Does the number of wires depend on the phase or the voltage? Thanks!

 

[dpc]

It depends on the number of phases. For 277V single-phase motor, you will need three wires - a hot, a neutral (white) and a ground (green).

Size will depend on the size of the motor. You can't assume #12 will be adequate. Conduit size depends on the size and quantity of the conductors in it.

 

[waross]

Single phase requires 2 wires.
Three phase requires 3 wires.
Single phase equipment using current at two voltages needs three wires. (electric ranges, electric clothes driers etc.)
The ground is extra.
You may find old installations where the ground and neutral were combined in one wire but I understand that this practice is now forbidden by the NEC. It has always been forbidden by the CEC in Canada.
yours

 

[alehman]

Neutral and ground were only allowed to be combined for electric range and clothes dryer branch circuits. And that practice has been prohibited in the last two NEC cycles.