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Looking to rent a bounce house for our son’s birthday and it requires a 20 amp circuit. The exterior outlet we would use is on half of a double pole 30 amp breaker, the other half being our tankless water heater and oven. Will this be safe and sufficient? And would it help at all to power off the tankless water heater while bounce house is on? Thanks.

UPDATE

I was wrong: this is not a gas oven. And the exterior outlet IS on its own 20A circuit. BUT I also discovered the microwave/wall oven combo unit requires 40A and I think it’s currently on 30A. Can someone please confirm the exterior outlet looks fine for bounce house as well as the bad news about the oven amps? I will get a pro out here to fix ASAP. Thank you.

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    Your location in the world. Having a tankless and an oven on half of a breaker seems not good/safe, plus the other half for an outlet, even worst. The 30 amp breaker would be too big if something was to happen, would not trip soon enough, so not safe. If in North America, I think you have bigger problems than powering a bounce house.
    – crip659
    Commented Jan 16, 2023 at 23:06
  • Notwithstanding other possible issues an overload for something like an obstructed blower motor developing 40A on a 20A breaker should trip in less than 90 seconds, 40A on a 30A breaker is dangerously close to the tolerance band where it might not trip at all until motor damage causes higher current. i.sstatic.net/I9zaK.jpg
    – NoSparksPlease
    Commented Jan 17, 2023 at 15:25

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Update

BUT I also discovered the microwave/wall oven combo unit requires 40A and I think it’s currently on 30A.

That's not necessarily a problem, because ovens and ranges are weird. A typical cooking element is only at full power right after you turn it on. The moment it reaches operating temperature, it starts cycling on and off at a "duty cycle" to maintain target setting. And you are unlikely to throw on all elements at the same time.

This "duty cycle" is allowed for in provisioning of power to ranges. There's a complex formula in NEC Article 220 (which covers commercial ranges as well as residential, and even covers things like a senior active living community that might have 500 ranges; allowing further favorable derate to allow that not everyone will cook at the exact same time).

So, since your breaker is lower than what you think it ought to be, I'd say don't worry about it. It would only be a problem if your particular cooking style is causing breaker trips, in which case NEC probably allows you to go larger. I wouldn't throw all the burners on at the same time to try to provoke a trip, that's a bit silly and defeats the purpose of the Article 220 favorable derates.

Original

Say what now?

30A breakers are NOT legal for:

  • gas ovens
  • gas tankless water heaters
  • Common receptacles (NEMA 5-15 socket)
  • "Common plus" receptacles with T neutral (NEMA 5-20 socket)
  • 50A sockets of any kind
  • NEMA 10-30 sockets unless only for an electric dryer AND installed prior to 1996

So it sounds like "the last guy" was overloading the circuit, and rather than use electricity responsibly, they replaced the breaker with a larger one, destroying the safety of the circuit.

No, it is not safe to do any of that.

You need to search both legs of the circuit to see what size of wires are being used. If any of it is copper #14 or aluminum #12, you need to use the correct 15A breaker.

If all of it is copper #12 or aluminum #10 or larger, then you can use a 15A or 20A breaker.

If all circuit branches have independent neutral wires all the way back to the panel, you can use single breakers.

If one leg has all 20A wire but the other leg has 15A wire, you can use separate size breakers - however if they are sharing a neutral you need a handle-tie between the breakers.

And then, since "the last guy" was a scary unsafe operator, search the house for any other wiring defects.

If the circuit to the outdoor outlet is indeed 20A wire (#12 copper or #10 aluminum) then you can use a NEMA 5-20 outlet there. Note that outdoor outlets need to be GFCI-protected, but there is more than one way to do that.

Running a bouncy castle without GFCI protection isn't even stupid.

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  • Thank you. The outdoor outlet has GFCI but your other remarks obviously concern me. I will try to post a pic of the breaker box before I involve electrician or landlord. This is a rental we just moved into so don’t want to rock the boat with a new landlord unless necessary. Obviously safety trumps that but want to be sure.
    – KFBR392
    Commented Jan 17, 2023 at 19:43
  • Updated my post with new info and pictures. Thanks again for your answer.
    – KFBR392
    Commented Jan 21, 2023 at 22:59
  • @KFBR392 OK. Updated.
    – Harper - Reinstate Monica
    Commented Jan 21, 2023 at 23:21
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I seriously doubt that a tankless water heater and an oven are on half of a double pole breaker unless they are gas appliances. More likely, they're on the full breaker and the outlet is bootlegged of the circuit incorrectly because it should never be on a 30 amp breaker. Find another 20 amp circuit and run the bounce house off it.

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    The oven and water heater could be gas.
    – nobody
    Commented Jan 17, 2023 at 0:57
  • @nobody Edited that into my answer.
    – JACK
    Commented Jan 17, 2023 at 2:05
  • Sorry, yes these are all gas appliances. But with @Harper’s answer above perhaps we’re better off renting a generator. Something I was trying to avoid but better to deal with its noise than electrical problems.
    – KFBR392
    Commented Jan 17, 2023 at 2:45
  • More important than renting the generator, @KFBR392, is getting the whole house checked for electrical issues. It'd probably be worth having an electrician come in for a few hundred bucks to find out what's been done wrong and get an estimate for repairs. You may be able to do some yourself, others might be better off having a pro do it.
    – FreeMan
    Commented Jan 17, 2023 at 14:47

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