I am rearranging some wiring on a boat dock, where there were two jet ski lifts that were powered with 220v originating in a sub-panel (at the house) which has a 20a GFCI two pole breaker.

I was a bit surprised to find a 110v outlet was powered by one leg of that circuit (which further downstream powers the two jet ski lifts). The outlet is not GFCI itself. A neutral and ground are provided (separately) and the wire looks appropriate (though I have yet to open up all the conduit involved).

My question is that outlet and the 2 pole GFCI. I am somewhat familiar with the Multiwire Branch Circuits rule, but not 2 pole GFCI breakers. Can such a breaker legitimately protect a single leg outlet? Logically I would think so (since logically a leak of one leg is the safety issue it should be protecting against anyway), but code is ... well, different at times.

Also: an outlet tester inserted in that outlet reads correctly, but hitting the GFCI test button fails to trip the breaker in the panel. That might indicate faulty panel breaker of course. But it made me wonder if this was really legit overall.

My original plan was to take the 4 wire run, use only three, swap the 2 pole GFCI for a single pole GFCI and turn those two jet ski locations into general purpose 110v outlets. If this setup is legit, I could use all four wires, and have twice the current capacity and not even need a new breaker (well, except that it might be defective -- should a outlet tester trip it?).

So I think this boils down to: where a GFCI is required, can a two pole breaker provide the protection for an outlet only on one leg?

Thanks for any insight,


  • does that 2 pole breaks break 2 lives or a neutral and a live? Nov 2, 2018 at 15:45
  • 1
    It breaks 2 lives. It is a 4 wire (L1, L2, Neutral, Ground) run out to the dock. I also did the obvious and hit the test button on the breaker and it is defective; the boat lift GFCI tests (a 30a of the same type) but the 20a I am working with does not. So while I still do not know if it's legal to use a 2 pole GFCI on a single leg outlet, I know THIS breaker is broken. A reminder to periodically test, which I had not been doing.
    – Linwood
    Nov 2, 2018 at 16:01
  • That setup is legal but since the breaker is faulty this poses a serious safety hazard. I would replace the breaker right away and turn it off until it can be replacrd, stray currents cause deaths around docks every year. The newer breakers have self test functions that if they fail the power is shut off for safety.
    – Ed Beal
    Nov 2, 2018 at 16:46
  • Well, it's all off as I am tearing it all apart anyway to trace the wiring and removing the jet ski lifts. Its making me nuts that they changed wire color repeatedly through junction boxes. Dock lights went black to white to yellow (so far).
    – Linwood
    Nov 2, 2018 at 17:28

1 Answer 1


Don't think of it as a 120V receptacle on a 240V circuit. Think of it as a 240V load on a multi-wire branch circuit.

That is a legitimate wiring method. MWBCs can also supply 240V-only loads.

There's one gotcha. You can't have any receptacles on a circuit where the hardwired loads account for more than 50% of the total circuit ampacity. That doesn't apply to cord-and-plug connected loads, so the workaround is to make the hardwired loads not hardwired anymore. Fit sockets, cords and plugs.

So you have an MWBC. If you employ a GFCI on an MWBC, you must do it with a 2-pole 120/240V GFCI breaker (or deadfront that is inline). You cannot use a European 2-wire RCBO, because all 3 wires, neutral included, must go through the GFCI's internal sensor together.

In any case, in a water related installation, you want the GFCI protection well before you get anywhere near the water. Because you want the wires protected also - if the wires get wet, they are protected, rather than electrifying the water and causing drownings.

  • I'm sorry, I am not familiar enough with the terminology. The breaker has a CH 2 pole breaker, which has L1 and L2 plus N run to it. L1, L2, Neutral and Ground then go to the conduit, where L1, Neutral and Ground are connected to a 110V outlet, L1, L2 and Ground continue to two separate motor loads further out. The question is whether that outlet is code compliant (given its location requires GFCI protection). I have simply never seen a 2 pole GFCI feed an outlet; it may be common, but when in doubt, ask; right?
    – Linwood
    Nov 2, 2018 at 16:38
  • Yes, that is all as I expected. I cleaned up my answer to be a little more clear. Everything you asked about is fine. The only gotcha I can think of will come from left field, the "no receptacles where hardwired loads exceed 50% of capacity" rule. In that case just alter the boat lifts so they plug in, haha! Nov 2, 2018 at 17:02
  • Well, the jet ski lifts (impacted by this) are coming out, so that's fine. I can just convert them to outlets, except as I continue to trace wiring (it changes color in each junction box, sadly), I found they didn't run neutral to the lifts, so it is not as simple as I hoped. I also found out the IDIOTS who did this had a "Dock light" breaker in the panel, which they have nothing connected to, and instead fed the dock lights off one leg of this run as well. Darn good thing no one every turned that off and trusted it as off. Thanks for the clarification.
    – Linwood
    Nov 2, 2018 at 17:22

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