Wiring the workshop, it'd be simplest to use the 220V circuit to also supply the shop's 110V outlets. I know some machines/appliances do that internally; can I expose it on the wall?

(I'm never sure whether to call it 110/220, which is what I heard as a kid, 120/240, or 115/230.... or if they're all recognised as nominal so it doesn't much matter except when planning wattage capacity.)

  • 1
    The technical term is "120/240V".
    – Tester101
    Aug 30, 2015 at 17:30
  • Are you talking about supplying both 120 volt and 240 volt loads, on the same circuit? Or do you want to split a 240 volt circuit, into two 120 volt circuits?
    – Tester101
    Aug 30, 2015 at 17:32
  • The question is whether I can cheat and use it both ways at once depending on what's plugged in and turned on, subject to current limits.
    – keshlam
    Aug 30, 2015 at 18:27

1 Answer 1


There are a few concerns:

Neutral and Grounding

First and foremost to do any of this would require a neutral conductor and a non current carrying conductor known as a ground/earth.

Undersized Grounding

Most double pole branch circuit grounds are only sized at #10. This is only good for up to 60 Amps according to the NEC. The total Amps gained with the 120 V outlets may exceed what the code allows for #10 grounding. If the existing double pole is rated at 50 Amps, than you have 10 Amps to spare before having to increase the size of the ground to a #8 If you plan on removing the double pole receptacle all together than there shouldn't be a problem with a undersized ground.

OverCurrent Protection

If the above criteria has been met and the existing double pole receptacle is protected by a double pole 15 or 20 Amp breaker then you can safely tap off the conductors at the junction box to fed other 120 V outlets.

However if the double pole receptacle is protected by a breaker greater than 20 Amps, then one solution would be to change the the double pole receptacle to a small main-lug sub-panel. Then branch off the sub-panel so each branch circuit is protected by its own breaker.

  • Understood re it being a four-wire circuit. Good point re beefing up ... did you really mean safety ground, or neutral? I believe the existing 240V circuit has a 30A breaker in each leg, back at the box, so yeah, subpanel is probably required to meet code. Darn; I was hoping to simplify a bit.
    – keshlam
    Aug 30, 2015 at 18:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.