I am trying to determine the most cost effective way to add a 30 amp breaker so that I can plug in and run the air conditioner unit on my RV. Currently my panel is full and I don't have space to put in a whole new panel. I do have a 40 amp hot tub breaker box located outside but don't think I can add anything to it. So is it possible to just add another 30 amp breaker to a full panel and then wire a 10 gauge plug to it?

I like the idea of adding something to the hottub box if I could just wire a plug in right off of that box. This is a picture of the hottub box. It is a Beachcomber GFCI box. It looks like it has an open spot. I would just have to turn the hottub off to run the RV I assume

Hot tub breaker outside

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Picture of hottub box information enter image description here

  • 1
    You don't have any place you could mount a subpanel? You could probably replace that 40A box outside with a subpanel with space for more breakers, then run a 30A receptacle off of that. You might not be able to run the hot tub and the AC at the same time, but the 40A breaker will still protect the wire. Or if you could run larger wire to that box, you could make it a 60, 70 or 100A subpanel. Commented Jul 11, 2015 at 19:33
  • Depending on your panel, you may be able to use "tandem" breakers: either two 120V breakers in the space of one (homedepot.com/p/…) or two 240V (double) breakers in the space of one. Not all panels allow these and some only allow them in some spaces so you should consult with an electrician. If you post a photo of your panel, we may be able to help.
    – DoxyLover
    Commented Jul 12, 2015 at 0:43
  • Can you post a picture of the hot tub box's label? That should tell us whether this thing accepts tandem breakers, or at the very least the model number. Commented Jul 12, 2015 at 16:43

1 Answer 1


You're in luck -- your panel can accept another 240V breaker in the bottom knockout pair. You'll need a 30A Siemens type QP breaker to install there, which you can pick up at a typical big-box store. (A GFCI is not needed here, best I can tell, because this is a single outlet in dedicated service.)

  • Planning to put a connector there for the RV to plug into? L 14-30 twist lock I assume. You can also use this plug to back feed the house with the generator upon extended power outage. Just be sure to keep the main breaker off when back feeding.
    – Trout
    Commented Jul 14, 2015 at 1:56
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    @Trout: no, just no. If you want a generator, get a transfer switch. Commented Jul 14, 2015 at 2:22
  • @ThreePhaseEel I was just thinking it's too bad you can't downvote a comment (about backfeeding the generator) into a 30A receptacle without a transfer switch... Commented Aug 9, 2015 at 21:35

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