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Looking for input on my garage rewiring project.

House built in early 1950's. A slightly roomy one-car garage. I want to modernize it and make it nice to work in; sometimes power tools and car tools, etc. Garage is attached to the house. No problem running cables from the breaker panel through basement joists to the garage.

Currently a single 15 amp circuit supplies this:

  • garage outlets (3, 1 of which is for door opener)
  • garage lights (3 porcelain ceiling fixtures)
  • exterior garage flood light (1)
  • exterior outlet (in backyard)

I'm thinking of doing this:

20 amp circuit:

  • 8 outlets (2 side wall, 3 back, 3 other side)

another 20 amp circuit:

  • garage lights
  • ceiling outlet for door opener
  • exterior garage flood light
  • 2 exterior outlets (one in backyard, one outside garage door)

Does this seem reasonable? Or should the 2nd circuit be split up?

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    Matter of opinion, more than anything. I personally prefer to keep the lighting on it's own circuit so that it's very unlikely that anything will take it out, leaving me in the dark with a tool that's still spinning. Perhaps leave the 15 amp to run lights and the opener (only) and add 20s, unless the 15 amp happens to be wired with 12Ga copper. – Ecnerwal Jan 28 '20 at 22:48
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    Be aware modifications must be to current code, which currently requires gfci protection in garages (and I've read 2020 NEC requires AFCI too). You might be better off leaving the old wires alone and adding one or two circuits for new receptacles. – NoSparksPlease Jan 28 '20 at 23:16
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    @Mike That info is dated, but so then might be your electrical code. 7 states still haven't adopted NEC 2014. – Harper - Reinstate Monica Jan 28 '20 at 23:49
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    You can use nine of them. Only the first one needs to be GFCI. – Harper - Reinstate Monica Jan 29 '20 at 4:34
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    It means you can install a GFCI device at the front of a circuit and connect the rest of the devices to the "load" terminals and then the rest of the circuit will be protected by that first device. – NoSparksPlease Jan 29 '20 at 16:09
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I'm not one to change stuff if it isn't already broken.

There's nothing wrong with the existing 15A circuit. I would leave it just as it is, and have a general sense that you'll try to avoid putting shop tools on it (since if the tool trips the breaker, it'll knock out the lights).

Then, I'd add the two 20A circuits as you propose, except have both of them feed outlets. The day you get a dust collector for your table saw, you'll thank me when you can just move the dust collector to the other circuit.

I would do one more thing, though. I would either run the second circuit with /3 cable, or have a notion to convert it to 240V/NEMA 6 if you ever get yourself a 240V tool. This is so you don't have to say "no" if you find a sweet table saw that's 240V, or don't wind up like that other person trying to run a nice big tool like a SawStop on 120V, and having all manner of problems as a result.

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    Actually did this 12/3 suggestion in my garage, at each receptacle location installed ivory receptacle on the black and white receptacle on the red, made it easy to identify and remember not to plug space heater into same outlet as my compressor. – NoSparksPlease Jan 29 '20 at 16:21
  • This is interesting. So it uses a single 12/3 cable to carry two circuits? Then at the panel black and common is one circuit and red and common is another? – Mike Jan 29 '20 at 23:41
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Circuit 1

Looks fine as-is. 20 amps for 8 receptacles is perfect. I would add the garage door opener to this as well (it's easier than you think). It's unlikely the opener will overtax your circuit.

Circuit 2

I would make this lights-only and downsize to 15 amps. This lets you run 14 gauge wire. Why downsize? Because if you make the circuit 20 amps, all your switch wires will need to be 12 gauge as well. And, as comments noted, the lights won't be taken out by a tripped breaker.

Circuit 3

Run NM wire until you hit your exterior box. Then add a GFCI and run UF cable from here to your garden receptacle.

  • Adding the opener to the 20 amp receptacle circuit will, in fact, be easy because of the current wiring layout...I just wasn't sure if that needed to be separate because of the load of the motor. – Mike Jan 28 '20 at 23:41

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