Electrical Troubleshooting Question:
My question is, how do you know when to use 12-2 cable versus 12-3 cable, 14-3 cable versus 14-2 cable.
I keep on getting confused on when to use 2 wire versus 3 wire.
Hi Matt - Great Electrical Repair Question!
2 and 3 wire cables can have several uses such as home run power feeds going back to the panel, branch feeds, single switching, 3-way switching, 4-way switching etc. It all depends on what you are wiring and what the electrical application will be.
As for circuits installed from the electrical panel, a 2-wire (black and white with the ground) cable will be used for one hot and one neutral or one circuit. However a 3-wire circuit (black, red, white and the ground) cable can be used for feeding two circuits that will share the neutral and ground wire.
This 2 circuit multi-wire configuration requires that the black and red hots be attached to a two-pole circuit breaker that has a tie-bar so that these two circuits are not fed from the same buss in the panel
This will ensure that the neutral wire load will be balanced and not become overloaded under normal circumstances. The voltage reading from black to red will be 240 volts because they are attached one to the two separate busses or phases, but the voltage reading from black to white/neutral or ground will be 120 volts and the same for the reading for the red wire to white/neutral or ground.
Be Careful and Be Safe, never work on energized circuits!