I'm thinking about running a single 12/3 cable to my garage to wires all of the outlets (8 or 9). (This is old construction, with a finished ceiling.) I understand that the black and red wires will create two circuits fed by a double-pole breaker. Will I still be able to install GFCI outlets at the beginning of each wall run? I've read that a GFCI breaker may be needed. I haven't decided if I'll do every other receptacle or the tops of all receptacles on one circuit and the bottoms on the other. By the way, each wall will likely be fed by its own cable, going back to a junction box.
Electrical – do two circuits on 12/3 and still have GFCI
electricalwiring
Related Solutions
I'm not sure what the codes are like in Canada, but here in the US the only problem you'll have is that you're using two separate breakers. Thought the problem can be overcome by installing a handle tie, to link the breakers together.
As for wiring the GFCIs, a diagram can be found in this answer.
Simply replacing the first receptacle in the group with a GFCI receptacle, will provide protection to the entire group (if wired properly).
GFCI Receptacle
Locate the feeders
WARNING:
This procedure should only be carried out by persons with the proper tools and knowledge. And should be carried out with extreme caution.
When you open up the box containing the first receptacle in the group, you're going to notice two cables enter the box. One cable brings power from the breaker/fuse box (feeder), and the other carries power to the remainder of the circuit. You'll have to figure out which cable is which, so you know how to connect the GFCI receptacle.
- Start by turning off the power at the breaker/fuse box.
- Disconnect the receptacle, and position all the wires so that they will not contact each other or anything else conductive.
- Turn the power back on.
- Using a multi-, voltage or non-contact meter determine which set of wires is which. The feed from the breaker/fuse box will have power, while the line going to the rest of the circuit will not.
- Mark the wires in some way, and turn the power back off.
WARNING:
If you got a voltage reading on more than one set of wires, STOP, do not follow the rest of these instructions. contact a local Electrician.
Connect the GFCI
On the GFCI receptacle you'll notice that one set of terminals is labeled "LINE", and the other is labeled "LOAD".
- Connect the wires from the cable you marked as being from the breaker/fuse box, to the terminals labeled "LINE" (Black to brass, white to silver, green/bare to green/ground and the box if it's metal).
- Connect the wires from the other cable to the terminals labeled "LOAD".
- Install the receptacle into the box.
- Turn the power on.
- Press the Reset button on the GFCI receptacle.
WARNING:
If the receptacle will not reset, the wiring is connected incorrectly, or contains a fault. Contact an Electrician to complete the job.
GFCI Breaker
Alternatively, you can install a GFCI breaker to protect the entire circuit.
WARNING:
This procedure should only be carried out by persons with the proper tools and knowledge. And should be carried out with extreme caution.
- Turn off the breaker.
- Remove the black wire from the terminal on the breaker.
- Locate the white "neutral" wire associated with the circuit (should originate from the same cable).
- Remove the white "neutral" wire from the neutral bus bar.
- Remove the breaker (Caution should be used not to touch the hot bus bar while the breaker is removed).
- Install the GFCI breaker.
- Connect the white wire from the GFCI breaker to the neutral bus bar.
- Connect the white "neutral" wire from the circuit to the GFCI breaker.
- Connect the black "hot" wire from the circuit to the GFCI breaker.
- Turn the breaker on.
WARNING:
If the breaker will not reset, the wiring is connected incorrectly, or contains a fault. Contact an Electrician to complete the job.
Test the GFCI
Once the GFCI device is installed, it should be tested at least once a month to insure it's functioning properly.
- Press the Test button.
- Press the Reset button.
If the GFCI will not reset, the GFCI is bad, the wiring is incorrect, or there is a fault. Correct any faults, and/or install a new GFCI device.
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Best Answer
This applies to all MWBCs
That type of configuration is called a multi-wire branch circuit (MWBC). In this arrangement, you connect a receptacle to one hot and the shared neutral. It is a Code requirement that neutral be pigtailed (i.e. don't use the receptacle as a splice block for neutral). The rule is to assure that neutral is not severed for the other half of the circuit. (this can cause all sorts of bad).
This applies to GFCI on MWBC
You can absolutely install GFCI+receptacles at the beginning of the wall run. You just won't be able to use the LOAD terminals to carry the circuit onward - you will need to pigtail both hot and neutral. Because you can't use the LOAD terminals, only those receps will have GFCI protection - you can't pass it downward to the remainder of the MWBC. You'll need one GFCI per outlet that you want to have GFCI protection.
If you want to GFCI-protect the whole circuit in one shot, use a GFCI breaker at the start, then plain receps throughout. . Mind you, the circuit may require AFCI also, in which case you'd use a GFCI+AFCI breaker.