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I have an unused 220V, 3 prong (2-conductor) dryer outlet in my garage and would like to convert that into 2 110V supplies to some overhead lights and a ceiling outlet for a garage door opener. How do I split that 30A 220V supply into a couple of different 110V 15A circuits? I don't expect any more than a couple hundred watts of intermittent load per circuit.

  • In all likelihood you would not be able to install a sub panel off the circuit because as described the current wiring does not sound like it has a separate safety ground. Any new installation of a panel is going to require a separate safety ground wire in addition to the neutral and two hot leads in order to be up to code. – Michael Karas Dec 11 '16 at 23:30
  • Can you run a separate ground wire back to the panel? – ThreePhaseEel Dec 11 '16 at 23:55
  • It's legal to do so. The ground can follow any viable route. It doesn't even need to go all the way back to the panel if it can reach an intermediate point with the same thickness or bigger ground going back to that same panel. – Harper - Reinstate Monica Dec 11 '16 at 23:57
  • So....I definitely need a 3-conductor supply? I haven't removed the cover off the outlet but in all likelihood looks like a 2-conductor situation. – Knob Scratcher Dec 12 '16 at 0:00
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    Can you take a photo of the inside of the dryer outlet box once you get the cover off? – ThreePhaseEel Dec 12 '16 at 4:21
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Depends how much work you want to do. The simplest approach given: " I don't expect any more than a couple hundred watts of intermittent load per circuit."

Is to convert it to a single 120V circuit at 20 amps, 2400W capacity; (or 15A, depending what the total expected wattage actually is) that happens to have vastly oversized wires. Replace the dual-pole 30A breaker with a single pole 20A breaker, use one of the hots (retagged green) to ground, [or retagged white to neutral if the current "neutral" wire is already at the main panel ground/neutral buss and it's more convenient to make THAT one the "green/ground" wire] change the receptacle, perhaps add a few boxes connected with at least 12Ga copper to house some additional outlets, away you go.

Now, if it's easy to run a ground wire, (or by some miracle the cable actually has one already, unused) you can do that and convert to a 4-prong, and then my answer in the "near duplicate" linked above applies. Several other options were provided that ignored that poster's desire not to do anything in the panel - if you are OK doing things in the panel, they also apply if you like them better. You could replace the receptacle with a sub-panel, for instance.

  • Safe perhaps but legal no. You're not allowed to re-mark hots to neutrals; or anything to ground. The only re-mark allowed is neutral to hot. I agree, I'd consider it, but when I've suggested it in the past, I've gotten downvoted! Anyway if feasible the retrofit-ground option is the much better way to go. Doesn't even need to go inside the panel; just to any other heavy ground path that does. – Harper - Reinstate Monica Dec 12 '16 at 16:58
  • Suppose you put white heat shrink (or green) on the ends of the wire. I would think that white electrical tape would be reasonable but of course it could be easily removed. Why is there a restriction on re-marking to neutral a wire which was originally color coded hot or anything to ground? – Jim Stewart Dec 12 '16 at 19:25
  • I did precisely as Ecnerwal stated above and replaced the dual-pole 30A breaker with a single pole 20A breaker, retagged one of the hots white and screwed it to the white to neutral buss bar, and now have a normal 120VAC circuit with vastly oversized wires. Perhaps not code as Harper states, but it works great, and is easy enough to convert back. – Knob Scratcher Jan 18 '17 at 19:04

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