Wiring – 15 amp gfci on 30 amp breakers

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I have 2 space heaters at opposite sides of my bathroom walls (facing into guest rooms). There is a wire that is easily accessible going between them thru the bathroom wall, which I have opened up right now. the space heaters are on a double 30 amp breakers (two 30amps tied together in the panel).

I would like to put a 15 amp (but I could use a 20amp or 30 amp if necessary) GFCI on the open wall to run hair appliances (not at the same time). Can I splice into that wire from one heater, to the GFCI and then back onto the 2nd heater?
The heaters are rarely used and haven't been turned on at all in a year or two.

Best Answer

  • Your standard receptacles must be 15A on a 15A circuit or 15A or 20A on a 20A circuit. Your plug-in appliances will all be designed for those type of receptacles (generally 15A and fit 15A or 20A).

  • GFCI is required for bathroom, but doesn't have to be at the receptacle - could be at the breaker.

  • You can't piggyback 15A or 20A receptacles on a 30A circuit (the heaters). Not allowed. Period.

  • You can repurpose the wires currently being used for the heaters to instead be used for 15A or 20A circuit. But to do that:

    • You will lose the ability to use the heaters - they will be disconnected.
    • You must replace the 30A circuit breaker with a 15A or 20A circuit breaker.
    • Any additional wire to extend the circuit must be at least 14 AWG (for 15A) or at least 12 AWG (for 20A).
    • Any junction between new wires and the old heater wires must be in an accessible junction box. (Not an issue if you are able to reroute the wires directly into the box for the new receptacles.)
    • 240V heaters often don't need neutral. If the existing wiring is only 2 wires + ground then you can only get a single circuit out of this - one wire as hot (on a new 15A or 20A breaker) and one wire as neutral. The neutral wire must be the white one. If the existing wiring includes neutral (e.g., black/red/white) then you can actually get two circuits out of this as an MWBC, but GFCI would have to be done at the breaker rather than at the receptacle.

The alternative of "pull power from the heat/fan" will probably not work. If the heat (lamp and fan are basically "nothing") uses more than a few Amps (I'm not sure of the breakpoint) then you can't put receptacles on the same circuit.

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