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I'm planning to run a four 10g wire 30 amp circuit to supply 240v for an electric dryer. I'm wondering if I can add a 120v outlet to this and only use one outlet at a time on the same circuit, instead of adding a separate dedicated 12g wire 120v circuit on a separate 20amp breaker. Is the possible?

Looking for the flexibility to switch between a 240v dryer and a 120v dryer without rewiring when the user switches their appliance. This is to be the solution to a laundry room's required 120v outlet.

This is for a residential service.

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There are scenarios where you can put 120 and 240v receptacles on the same multiwire branch circuit, but the catch here is that it is not Code legal to put a 15 or 20A receptacle on a 30A circuit.

Imagine a 120v/1500w dryer element goes short drawing triple the current putting out triple the heat. 4500w/120v = 37.5A. Looking at a breaker trip curve a 20A breaker should trip in 30 to 90 seconds. A 30A breaker could trip as soon as 3 minutes, or it might not trip at all since less than 25% over rating is actually within NEMA's wide tolerance for circuit breakers.

Also NEC 210.11(C)(2) specifies a "20-ampere branch circuit" for laundry, so it wouldn't satisfy the code requirement.

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  • Sounds like what is plugged into the 120v receptacle needs to be protected by a 20v breaker because the appliance power cord could be 12g?
    – simgineer
    Sep 11, 2021 at 14:54
  • That's part of it, all the wire insulation inside the dryer is sized for the overcurrent rating too. Sometimes is rattles my head to think breakers are allowed to draw 300% for up to 30 seconds.
    – NoSparksPlease
    Sep 11, 2021 at 15:14
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I'd just add an extra outlet to the 120V circuit that's already required in the laundry area

Instead of jumping thru hoops to try to wedge a subpanel into the laundry area (which is what you'd have to do to make your proposal Code-legal), I'd simply run a short length of Wiremold from the existing washing machine outlet to a surface box behind the dryer and put another outlet there, wired to the existing 120V circuit that powers the washing machine.

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  • That's a good idea. While the NEC says the laundry area requires at least 1 20amp 120v circuit, it doesn't need to dedicated solely to the washing machine. Of course, as said, an electric dryer requires a dedicated circuit.
    – George Anderson
    Sep 11, 2021 at 15:19

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