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I'm wiring my shed. There is a sub panel out back with a 20A breaker that supplies power to my pool light. I tapped that line to run the power to my shed because it's already ran about 3/4 of the distance. I used 12 gauge wire from the junction box near the pool to the shed, but 14 gauge wire in the shed. I didn't realize it was a 20A breaker until about half the wiring in the shed was done.

Rather than redo what I've already done in the shed, I thought about just swapping out the 20A breaker for a 15A breaker. The load will be:

  1. The pool light (2.5 amps)
  2. Five lights on the shed (3 outside, 2 inside)
  3. Four outlets

The alternative would be to rewire the shed and keep the 20A breaker, but I don't want to do that since I really don't need 20A of power out there.

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  • Well if you use a cabinet saw in that shed then obviously not... So question is: How large is this shed, will it realistically ever house a workshop (yours or next owner)? "Shed" is anything from a 4x11' brick hutch to a barn. – user3445853 Oct 23 '19 at 10:09
  • You could install a secondary breaker box at the point of take-off. – Hot Licks Oct 23 '19 at 22:55
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That's fine. The breaker protects the wire, and it's always allowed to use larger wire than you need, so bumping the breaker down to 15A is legal. Based on your anticipated load, it sounds like you won't have a problem with the breaker tripping.

The one issue you may have is if you intend to run a space heater on one of the shed outlets sometimes -- they usually use a whole 15A circuit by themselves, so that wouldn't be compatible with also having the lights on the circuit. However, that would just trip the breaker and wouldn't present a safety issue.

Note that since you have pool lights on this circuit, it'll need to be GFCI protected. If your current 20A breaker is a GFCI breaker, replace it with a 15A GFCI breaker. If it's a normal breaker currently, you probably have a GFCI somewhere downstream (though check this, and rectify if not), so replacing with another regular breaker is probably okay, but doubling up on the GFCI is allowed, so you're welcome to use a 15A GFCI breaker in either case.

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  • 1
    Thanks... And yes, it's currently a normal breaker, but it's run through a GFI outlet in the subpanel. I'll probably go GFI breaker anyway just to be safe. Thanks for your response. – Kevin Bright Oct 23 '19 at 1:08
  • Other high load devices in sheds might be power tools (circular saws), dust collectors, etc. Anything workshop-y will probably need more than 15A. @KevinBright Also note that GFI breakers can false-trip with certain types of load (inductive loads - saws, compressor motors, pumps, etc). You certainly want it for the pool lights, but not necessarily for things you might be using in the shed. You might consider one GFI outlet in the shed to feed (and protect) the line going to the pool, but leave some outlets in the shed not GFI protected. – J... Oct 23 '19 at 18:07
  • @J..., true, a workshop will need much more power, but I was inferring based on the plan for no 240V and only 4 outlets that a workshop was not being considered. – Nate S. Oct 23 '19 at 18:11
  • @NateStrickland Well, even if it's just for occasional use, a single table saw can easily require everything a 15A circuit can give. Once you start sharing that with lights, etc, it's very easy to overload the circuit. Even if OP doesn't have workshop ambitions for the space, simply having intention to occasionally use a high-load device (like a saw, etc) might be enough to trigger a reconsideration of the circuit layout. – J... Oct 23 '19 at 19:44
  • @J..., true, though temporary occasional use of a high powered tool could also be solved by running an extension cord from the house. It just depends if OP wants to pay extra now for the convenience of not having to do that later, if it ever comes up. – Nate S. Oct 23 '19 at 19:52

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