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Hoping to wire up a shed/workshop with two 15 amp circuits coming from a 60 amp sub panel beside the main panel. Wondering what type of wire I can use in PVC conduit and if it should be GFCI protected. If yes is it better to have a breaker that has GFCI capabilities or just start each circuit in the shed with a GFCI outlet?

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    Hello and welcome. The question currently is a little broad to answer -- there are a lot of ways to do it, and which one is best depends on some more details. Can you edit your question to add: 1. What loads you expect in the workshop (welder? dust collector? space heater?) 2. Is this workshop attached to your house, or a separate outbuilding? 3. If outbuilding, is the subpanel at the house or the workshop? – Nate S. Oct 24 '19 at 0:01
  • What all are you trying to stick in this workshop, and do you plan to keep the lighting and outlets separate? – ThreePhaseEel Oct 24 '19 at 0:08
  • Also, have you already trenched in the conduit, or is that something you have yet to do? – ThreePhaseEel Oct 24 '19 at 2:16
  • I'd like to keep the lights and outlets on two seperate circuits...however I was thinking of leaving one outlet on the light circuit because I was thinking since I'll install all LEDs that maybe I'd be able to run the compressor on the light circuit so the kick on wouldn't affect the circuit while other tools would be running. – Trevor Oct 24 '19 at 10:51
  • @Trevor -- do you have any objections to putting a subpanel at the shed? Is there a reason you put in such a tiny subpanel (60A panels are spa-box-sized) in the main house, for that matter? – ThreePhaseEel Oct 29 '19 at 1:39
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TLDR

Use THWN-2 #12 stranded wire.

Use six wires: black white red blue gray and green/bare.

Green/bare is ground for both circuits.

At the ends (once they are installed) wrap the black/white/red with electrical tape to group them. Also wrap the blue/gray.

On the lighting circuit, gray is neutral and blue is hot. No need for GFCI here.

On the outlet circuit, white is neutral and black and red are both hots. Cap off red for now on both ends. If you're not doing GFCI, get a 2-pole breaker (handles tied!) and punch the black down on one side and don't use the other yet. If you do GFCI, get a 1-pole for now because 2-poles are expensive. The red wire is there to make it legal, and gives you a spare circuit.

You can't run two of the same type of circuit to an outbuilding.

So you can't have two 15A 120V circuits to the shed. Nor can you have a 15A/120V and a 30A/120V circuit (e.g. for a travel trailer) - the amps are different

However you can have two different types of circuits:

  • One 15A receptacle circuit and one 15A switched lighting circuit
  • One 15A receptacle circuit and a 240V utility circuit
  • A 240V compressor circuit and a 240V pump circuit because the pump is switched on/off by equipment in the house
  • One 15A receptacle circuit and a 120/240V multi-wire branch circuit providing two 20A subcircuits

For instance I would run a 20A multi-wire branch circuit providing two legs of 120V that you seek. That counts as one circuit for the above discussion. However, this requires a circuit breaker that would most likely common-trip, so you'd lose the lights when the saw tripped the breaker. If that's what you want, then you may want to consider a MWBC for the power (strictly to avoid the same-circuit requirement) then a plain 120V circuit for lighting.

Another option in the LED age is to use 240V for lighting.

Wiring

Wiring wise, since you are in conduit, you run individual THHN type wires (actually THWN-2 but they'll be cross-labeled). For instance in an MWBC, you'd run black-white-red, and for a 120V circuit you'd run blue/gray. (gray is a neutral color).

1 ground large enough for the largest circuit; you can share grounds because you're only expecting to have a ground fault on one circuit at ta time.

Subpanel

If you foresee any need to expand beyond that, then you should install a subpanel in the shed. I gather that you have a 60A subpanel next to your main becuase it is full. Also, 60A implies it is very small in terms of spaces, so it's a stop-gap, not a long-term solution.

We preach "you want lots of spaces" pretty loud around here, so if it were me, I'd replace the 60A with a much larger panel in terms of spaces. I'd aim for 45-ish spaces in a typical house. So if your panel is 24 space, 18-24 space is good; if 16, aim for a 30-space panel. Then move the old 60A subpanel to the shed.

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  • Your first paragraph is very interesting. I did not know that and luckily, I never did that.+ – JACK Oct 24 '19 at 3:13
  • So it would be okay to run two 15 amp separate circuits as long as I don't have an outlet on the light circuit? I'm also a bit confused about the wiring...what kind of wire would I need to go from the breakers in the panel (under ground and in PVC conduit) to the shed? I'm assuming I can use 14/2 wire once inside the shed for both circuits. Also power should come into the shed on the light switch then branch off from there to other light switchs? Ideally I was thinking about 10 led 11w pot lights and 2 led lights on the outside of the shed all with seperate switchs. (3 switchs total) – Trevor Oct 24 '19 at 14:55
  • Also do I protect the circuits with GFCI breakers then? – Trevor Oct 24 '19 at 14:56
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I wired up my shed by putting the sub panel in the shed. Then I used a 30A 2P GFCI breaker in my house panel to feed that sub with #10 wire and have just 4 1-pole 15A breakers in that sub-panel. But all I am using in my shed is lights, a fan, 4 duplex receptacles and a small window A/C unit. The shed receptacles do need to be GFCI protected, so GFCI outlets are less expensive than GFCI breakers, plus if it trips, it can be reset right there, as opposed to being reset at the sub panel (which in your case may be in another building). But if you have multiple circuits, each individual circuit must have a GFCI receptacle, at least at the first one in the string, so that may end up costing more depending on how you do it. If you go my way, only the one Main has to have it.

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