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I have a outlet that is 240V with 4 wires. I want to change it to 3 wires, I am assuming the black is also a hot wire. With the volt meter I get 220V touching the two red wires and 110V when i touch the black to ground.

I want to change the plug to a 3 wire and I am not sure what to do with the black wire, can i just put a wire nut on it and push in the box?? Any help would greatly be appreciated. I don't need another shocking experience

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    That is very strange that you're getting 110 volts from black to ground. What are you getting from black to each red? What type is your current outlet? How about a photo of the front of your current outlet? – DoxyLover Dec 30 '16 at 23:46
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    Can you get us a photo looking into the back of the current box? Also, what type is that outlet? It looks like it can't be a NEMA 10 or a NEMA 14 from the back housing shown... – ThreePhaseEel Dec 31 '16 at 0:13
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    What kind of device is that? If it is a range or electric clothes dryer, I though a 4 to 3 wire conversion is not in the spirit of electrical code. – wallyk Dec 31 '16 at 0:38
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    What appliance do you want to power through this receptacle? – Jim Stewart Dec 31 '16 at 0:41
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    @RonGinn -- can you please get us a photo of the front of the current receptacle? – ThreePhaseEel Dec 31 '16 at 16:12
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It looks like your wires are in conduit. You need to follow the wires a bit more and figure out what they're being used for. They should go back to a circuit breaker, and it should be a 2-pole (240V) breaker. Turning off that breaker should turn off two of the wires. I have no idea what's going on with the third (black) wire.

Those are the two wires to put on L1 and L2 on your NEMA 6-20 receptacle. The ground goes to ground obviously. NEMA 6 does not use neutral.

  • That is what I thought, I did not think there was a neutral in 220 v. – Ron Ginn Dec 31 '16 at 4:16
  • and yes they are in conduit, and they do go to the 240v breaker, the black wire I am not sure but there is voltage there to ground 110v. – Ron Ginn Dec 31 '16 at 4:19
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    110V to ground will be true for any "hot" in a 110/220 (aka 120/240) split-phase system. Ground is center-tap on the transformer (same as neutral by the way). The black wire is a real wildcard. What exactly was the old connector? I'm unclear why it has 3 hots and a ground going to 4 different terminals. – Harper Dec 31 '16 at 5:09
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    Looking at the terminal connector on the ground are you in a country that has 3 phase power? If black to ground is 120 what is black to red 1 and black to red 2? On a 4 wire usually 1 is neutral, 1 ground and the 2 hotts. If it were 3 phase you would see similar voltages red 1 to black as red to black and red to red. – Ed Beal Jan 1 '17 at 8:00

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