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I have a 30Amp 240V (4 wires) circuit. And I want to branch a single 120V 20A outlet on this circuit for convenience. I was hoping to find a Decora compatible breaker that I can used to protect the 20A outlet. Such that I would have a 3 slots box with:

  1. A 30 Amp 240V Outlet connected to the 10GA wires
  2. A 20 Amp breaker connected to one hot leg of the 30A circuit with 10GA.
  3. A 20 Amp 120V outlet connected to the breaker.

My understanding is that this setup would be code compliant but that type of "switch box breaker" doesn't seem to be a thing. Any ideas? I'm I thinking of this wrong?

Context: This circuit is intended to power an electric grill but having a 120V in that location would be convenient as well to power yard tools and such when the grill is not in use or power some low power things like string lights the grill is in use (or not for decorative lights in the winter).

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    What is the 30 amp circuit used for? That size is usually just for one device. Plugging in a kettle with the dryer(common use) running would not be good.
    – crip659
    Aug 4 at 18:50
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    I believe you may be referring to a sub-panel. More info on what you are trying to accomplish providing power to would help.
    – RMDman
    Aug 4 at 19:32
  • Thanks @crip659. I've added this context to the question: This circuit is intended to power an electric grill but having a 120V in that location would be convenient as well to power yard tools and such when the grill is not in use or power some low power things like string lights when the grill is in use.
    – Nicolas Guillaume
    Aug 4 at 20:13
  • @RMDman Yeah I could do this with a 60Amp sub panel. but I was hoping to avoid the ugly box for a single breaker... My plan B is to use something like that: amazon.com/gp/product/B00002N7KR
    – Nicolas Guillaume
    Aug 4 at 20:15
  • The problem with subpanels is not "ugly". At least not as far as I'm concerned. The problem is clearance. You need a 30" wide by 36" deep clear space - technically "nothing", but certainly nothing fixed in place (cabinets, shelving, workbench, etc.) and nothing big & heavy. If you have the space then a subpanel is a relatively simple and code-compliant solution. You can even have a 30A (or 40A or 50A) subpanel by using a 60A (or larger) rated panel as long as the feed breaker (in the main panel) is matched to the wire size. Plus you can use aluminum between the panels to save money.
    – manassehkatz-Moving 2 Codidact
    Aug 4 at 20:23

2 Answers 2

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Other than typically being set up for 50A 240V & 120V 30A, (along with one or two 120V 20A) an "RV Subpanel" would be a clean way to do this. If you can find one where you can change out the NEMA14-50 for either a NEMA 14-30 or 14-30L or 6-30 or 6-30L (depending which you use for the grill) and change the 50A breaker for a 30A breaker, it's all there in one clean package.

RV Sub-panelImage from https://rvsitesinhomer.com/wp-content/uploads/2017/12/IMG_5639.jpg no endorsement implied.

In any case you need the working space for a sub-panel. Which is likely not a problem outside (30" wide, 36 inches in front, and a bit more than 6 feet above, kept clear, not used for storage.)

It may well be easier or less expense (certainly less changing out parts that don't do what you want) to get what you want with a small sub-panel and a couple of outlet boxes, if a bit less "streamlined, all in one."

As outside circuits, GFCI protection is mandatory (as well as "a good idea.") Potentially that could be done at the feed breaker inside, which may prove more reliable, due to being dry.

An alternate possibility is to simply run conduit from inside with 2 additional 12AWG wires in it for the 20A circuit, and keep all the circuit breakers/GFCIs inside the building, so you only have to deal with weatherproof boxes and in-use covers for the receptacles.

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    Thanks for this recommendation. I did look into the RV subpanels but they are pretty bulky and overkill. I was honestly hoping to find a code compliant solution that fits in a 3 Gang box but a 60Amp rated panel is much smaller and I could have 2 outlets next to it. The feeder breaker is already a dual pole 30Amp GFCI breaker so I'm good on that front. Running a new circuit isn't really an option since I don't have a conduit between the junction box and the panel otherwise I would just do that.
    – Nicolas Guillaume
    Aug 4 at 21:46
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    @NicolasGuillaume even if you find something smaller, you're going to end up needing clearance space for a subpanel because that's what it will be. Might be time to run a new conduit.
    – KMJ
    Aug 4 at 22:05
  • @NicolasGuillaume Remember with 10 gauge wires you still only have 30 amps to play with. There is no problem hooking up a 60 amp panel to a 30 amp breaker.
    – crip659
    Aug 4 at 23:43
  • Or, you know, run it in THHN and you get 40.... except "I don't have a conduit between the junction box and the panel" - well then this gets stupid real quick. "Might be time to run a new conduit" +1.
    – Mazura
    Aug 5 at 20:38
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Adapter and Bob's your uncle.

They make UL listed adapters with a 14-30 plug and multiple 5-15 (normal) sockets. Secret: they have internal fuses instead of a breaker.

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