I'm adding new wiring for a new spa. This is in WA state with City of Bellevue being the AHJ, which is currently under NEC 2020.

The spa comes with a QO6-12L100TRB sub-panel with 30A and 20A 240V GFCI breakers already installed. The installation instructions say to run 3-#8 CU wires + ground from a 50A 240V (non-GFCI) breaker in the main panel to this sub-panel.

680.22(A)(1) requires a 120V 15 or 20A GFCI-protected outlet 6-10' from the spa on a general purpose branch circuit. Since Table 210.3 (Special-Purpose Branch Circuits) says nothing about a circuit for a spa, does this 50A branch circuit qualify as a general purpose branch circuit? I.e., can I add a 20A 120V GFCI breaker to my subpanel to feed the required receptacle or must this be on a different branch circuit? Assuming I can add the breaker and receptable in the same sub-panel, can I still do that with a 50A breaker at the main panel and 3-#8 CU wires to the sub-panel or would I then have to switch to a 60A breaker and #6 CU wires?

Assuming it is reasonable to add a breaker for the required receptable in to the shipped spa sub-panel, I can either add a GFCI breaker or use a GFCI protected weather-resistant outlet. Other than cost, any reason to pick one approach over the other?

I wish NEC gave some rationale for that required receptable. My guess is it's for servicing the spa or some such thing. I suspect it will rarely be used and when used, even more rarely be used while the spa is drawing its full 50A, so it seems just adding a 120V breaker should be fine. Assuming so, I certainly understand the advantages of upsizing the branch circuit in case I ever have other things I want to do near there, but as it is, pulling the wires from the main to the sub-panel is already going to be challenging and I'd rather not make the job any harder than needed, so that's why I'm looking for what's required, not what might be nice to do for future-proofing. Feel free to try to convince me, but also please let me know the minimum requirement. Thanks!

  • You can add it to the subpanel - you'll like it when you want to plug in a phone charger. But it seems odd that they would specify 8 AWG copper. Normally from main panel to subpanel you can use aluminum. 6 AWG aluminum is likely to be significantly cheaper than 8 AWG copper. Breaker in this case makes sense for the GFCI - a little more expensive but likely to last longer than a GFCI/receptacle. Jun 28, 2023 at 17:01
  • I agree w/ 6 AL. Instructions call for 8 CU but that's from the spa company. I'm fairly certain Square D is fine with either. But, again, I will likely go with the added cost to have slightly thinner wire for my challenging pull job through attic, wall, crawlspace etc. Jun 28, 2023 at 17:20
  • See this table Keep in mind that if you use standard NM cable ("Romex") then you actually need 6 AWG copper and need to transition to 8 AWG USE cable for the outside portion. Or use THWN wires in conduit - but then you need conduit. Jun 28, 2023 at 17:42
  • I wish NEC gave some rationale for that required receptable. They don't, for the same reason a lot of times govt. won't give "reasons" for regulations. If you have a stated reason then you'll convince yourself that it doesn't apply to you, which inevitably will lead to problems down the road. Jun 28, 2023 at 20:51
  • The "50A breaker at the main panel" source is a feeder circuit, rather than a branch circuit, because its role is to supply power to a subpanel. The included 20A GFCI breaker, if not otherwise needed for the spa, could supply your required 120 V receptacle. Just use one of its hot legs and the neutral, with nothing connected to the other hot leg.
    – Greg Hill
    Jun 28, 2023 at 23:19

1 Answer 1

  • #8 copper NM-B or UF-B is only good to 40A.
  • #8 copper anything else is good to 50A, as is #6 aluminum.
  • #6 copper NM-B or UF-B is 55A.
  • #6 copper anything else is good to 65A.
  • #4 aluminum is 65A.
  • #2 aluminum is 90A.

Note that copper is 4 times the density of aluminum, and as such is stiffer. As such, cables of similar ampacity tend to be about the same flexibility.

Since they are using a bog-standard "QO" type panel, feel free to swap that for a QO panel with more breaker spaces. You're not confined to only hot-tub loads here. I say that purely as an aside; we love big panels around here because having spaces for other things is always handy, and being out of spaces is a frustrating problem. That's why I thought it worth mentioning the larger wire sizes such as the affordable #2 aluminum. That would allow you to place other loads out there, such as a heat pump or EV charging in addition to the receptacle circuit.

I can either add a GFCI breaker or use a GFCI protected weather-resistant outlet. Other than cost, any reason to pick one approach over the other?

The GFCI breaker will protect the wires to the outlet, in case they get wet.

I wish NEC gave some rationale for that required receptable.

Because #1 maintenance, and #2 if you don't, people will run extension cords from a receptacle elsewhere that may not be GFCI protected.

  • Ugh. Cheapest wire is SER 6/3 AL. From one vendor, they say it's rated for wet and dry locations. From the main panel, the wire would run ~70' through attic, wall, crawlspace. Then, it would exit through the rim joist and go about 10' below a deck before entering the subpanel which is attached to the deck's ledger board. There is already UF under the deck, so I assume SER can be attached directly under the deck. spa sits on a concrete slab beyond the deck, do ~4' lower than the deck. Jun 29, 2023 at 0:41
  • Spa requires both the dual 30A and dual 20A breakers. There is room for 2-3 more single breakers, so I'd put a single 20A there. Jun 29, 2023 at 0:44
  • @Tom Yeah that's fine, as long as the SER isn't going underground. Jun 29, 2023 at 0:48

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.