I just removed a hot tub spa from my backyard. I am wondering if I might be able to use the 6/3 cable for an outdoor electrical outlet?

Could I change the breaker to a 120v 20 amp breaker. Then attach a UL outlet to the other end?

Thanks for any advice, ~Jeremy

P.S. I am in Oregon, USA


Sure, you're always allowed to use oversize wire. You are designating the circuit 20A, you could use anything 12 gauge and up. This is absolutely fine, there is nothing wrong with this, in fact it's a good idea if it's a long run and copper is no object.

You just have to contend with physical issues: the outlet (and possibly the breaker) is not listed to accept 6 gauge wire. Just pigtail the outlet with 12ga wire and use a connector listed to join 12ga wire to 6ga wire such as Ideal 76B (their red wire-nut).

I don't think you'll have box fill issues for one outlet, but you'll have to start thinking about that if you branch off any more wires. Outdoor boxes are often larger than indoor ones. If you're not using the existing box, you'll want to use at least a 2-gang box that's deep - most outdoor boxes should suffice. Thanks Speedy.

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    For 3- #6, one #10, and a device, you'd need around 27.5 cu/in box volume. Can you think of a single gang box that has that kind of volume without an extension collar? – Speedy Petey Apr 25 '16 at 1:06
  • The existing installation already came to a box, right? I don't assume he plans to downsize boxes... – Harper - Reinstate Monica Apr 25 '16 at 1:10
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    This was a hot tub install. What do you think the possibility is of there being a proper device box there? Almost certainly this terminated in a disconnect or breaker enclosure of some sort. – Speedy Petey Apr 25 '16 at 1:12
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    Or he may go beyond the disconnect enclosure to a new box, in which case he'd splice in the old enclosure. – Harper - Reinstate Monica Apr 25 '16 at 1:13

Yes, you can use that circuit to feed an outdoor outlet. However, there are several challenges which depend upon the choices you make.

The easiest would be to reuse the yard end cutoff switchbox as a subpanel. That way it can easily accommodate #6 wire. If it was wired as 240 volts with a neutral (white wire besides red, black, and bare or green), it could provide several 120 volt outlets and also provide 240 volts to a high power item like a heavy duty air compressor, welder, electric dryer, etc. If it was wired for 120 volts, then all you get is 120 volts, though you could have several outlets in separate sub-circuits. #6 wire is normally good for 50 amps, so you could have three 20 amp sub-circuits.

If you will be dispensing with the outdoor cutoff switch and GFI box, you'll have to replace it with some sort of housing for the outlet. A #6 wire will not fit into a 15 or 20 amp outlet terminals or quick connectors. It will need to be pigtailed to #12 wire (or #14). That requires a larger than normal box to fit the wire plus connectors into it. You also have to swap the circuit breaker feeding it with either 15 amp or 20 amp and again the #6 wire almost certainly will not fit directly into the breaker's terminal. So the #6 will need to be pigtailed to #12 or #14—preferably the same pigtail as used at the outlet end— into the circuit breaker.

An outdoor outlet definitely needs GFI protection. That can be provided by the outlet, but it is better that the main panel circuit breaker provide it.

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    Why is it better to use a GFI breaker as opposed to a receptacle? – Speedy Petey Apr 25 '16 at 1:07
  • More expensive anyway, not necessarily better. – ArchonOSX Apr 25 '16 at 1:26
  • @SpeedyPetey: Because a wire outside could end up underwater or whatever and it would be less safe to depend on a receptacle at the end than at the source to protect it. – wallyk Apr 25 '16 at 4:09
  • @wallyk, first off, I'm not sure how a receptacle a foot or two off the ground could wind up under water, barring being in an active flood plain. If this is your only rationale I find it questionable at best. ...... There is NO difference in safety between a GFI receptacle and GFI breaker. – Speedy Petey Apr 25 '16 at 11:20
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    @SpeedyPetey I think wallyk's point is that a GFCI breaker would also protect against ground-faults on the feeder, whereas a GFCI receptacle only protects the wiring after the device (plugged in items, etc.). – Tester101 Apr 25 '16 at 14:32

It's not the best idea but it is perfectly legal. Make sure your boxes are all rated to handle the capacity of all the #6 wire in it along with the receptacle(s). This is one of the reasons it is not the best idea, too many issues like box fill to take into account. It may be easier to splice the cable to a length of 12/2 inside and feed that to an outside box.

The breakers may not handle the #6 so you'll need to splice it to #12 tails, and the receptacle (GFCI) will definitely not so same situation.

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Unfortunatly, a 20 amp breaker is not rated for #6 wire but you could pigtail the wire with #12.

Not very pretty but actually legal by the code.

You will then have to pigtail the receptacle with #12 also.

Here is the problem, with 3 #6s and a pigtailed receptacle you would need at least 19.5 cubic inches of box space. Even a deep device box is only 18 in3. You would need a 4" square box 1 ½" deep or deeper.

With 2 #6 and a #8 ground and the receptacle pigtailed to #12 wire you would need 17.5 cubic inches and a deep device box would work. Or you will again need a 4" square or round box.

Now, weatherproof boxes don't normally come in these sizes so good luck finding something weatherproof for a receptacle that is this large. (You might be able to use a 2 gang deep FS box with a cover for a single receptacle.)

Anyway, good luck!

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You can always use larger size wire, however, you may run into a few problems doing so.

Terminal size

The fist problem you'll have, is that the 6 AWG wire cannot be directly terminated at the new 20 ampere breaker. 20 ampere breakers tend to only accept 14 AWG to 8 AWG wire, though this may vary a bit by brand. To solve this, you're going to have to use some smaller wire as a pigtail, to make the connection to the breaker.

You'll run into the same problem at the receptacle, as most 20 ampere receptacles only accept 14 AWG to 10 AWG wire.

Box fill

Since device boxes aren't designed to handle 6 AWG conductors, you're likely going to have trouble fitting all the wires in a normal single gang device box.

If you decide to install a single receptacle, and cap off one of the ungrounded conductors. You're going to need a box that has a volume of at least 24.5 cubic inches.

Three 6 AWG current carrying conductors @ 5.00 cu.in. per = 15 cu.in.
Grounding conductors based on largest conductor = 5 cu.in.
Device @ 2 times largest conductor connected to it (12 AWG) = 4.5 cu.in.
Total = 24.5 cu.in.

To make matters worse, you'll probably be looking for a weatherproof box, since you're installing it outside.

If you want to make the splice in a junction box, and then run 12 AWG to a device box. The junction box will also have to have a volume of 24.5 cubic inches.

Three 6 AWG current carrying conductors @ 5.00 cu.in. per = 15 cu.in.
Grounding conductors based on largest conductor = 5 cu.in.
Two 12 AWG current carrying conductors @ 2.25 cu.in. = 4.5 cu.in.
Total = 24.5 cu.in.

Which means you could use a 4 11/16" x 1 1/4" box for the splice. Then you'd continue to the device box with 12 AWG conductors, which would fit just fine in any device box.

So, can it be done? Sure. Is it simple and straightforward? Not really.

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