can 10-2 wire be used for a 120 circut?

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  #1  
Old 03-19-13, 01:50 PM
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can 10-2 wire be used for a 120 circut?

i am doing some renovation and plan on moving a existing 10-2 240v bx cable to another location specifically for use by an air conditioner. i do not plan on ever using a 240v air conditioner so rather than spend the extra $$ on new cable can i use the the perfectly good 10ga wire with a 120 outlet and just switch the breaker in the panel to 120.

if its OK what size breaker for 10ga? still 20a?

i am assuming that its not going to harm anything by using a larger than necessary wire?

thanks
 
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Old 03-19-13, 02:03 PM
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I am not an electrician, but there's a double-gang box on the outside of my workshop wired this way from the time I bought the place. Looks like it was a 240V setup for an RV for "shore power", that was later converted to 120V by repurposing a hot as a neutral and wiring that wire to the neutral bus bar.

It is not code to relabel wire color with colored electrical tape for a different purpose for 6AWG and smaller, but that doesn't mean that it won't function. I assume that the biggest safety concern in relabeling is making it clear and concise to any future electricians that work on the circuit or box that it's indeed wired this way. There could also possibly be problems later if your area requires inspections- an electrician might not take the job on other things that require working on this panel without fixing this correctly if he has concern that an inspector will take issue with this.

I assume that you would size the breaker for the receptacle. If you put in a 20A 120V receptacle, you'd use a 20A breaker. 15A receptacle, 15A breaker.

You also may have some trouble identifying which conductor is which, it needs to be determined so that hot is indeed wired to hot, and neutral is indeed neutral.
 
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Old 03-19-13, 04:17 PM
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Yes. Just use a single polr breaker and connect the white to the neutral bar and black to the breaker. Ground remains as is. I would snuggest a back wired* commercial receptacle because it would be a son-of-a-gun to get a #10 wrapped around a screw.

*That's back wired not back stabbed. Back wired the wires go under terminal plates that are tightened down by screws.
 
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Old 03-19-13, 11:54 PM
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got it thanks

just pulled the wire tonight and realized that it was only 12-2 bx wired as 240 to a double pole 20a breaker. i know this house was wired in the late 1960's and the two 240 circuits in the house are both "2 lead" wire with ground going to the metal bx box itself.

by today's standards should all 240 runs be three wire?
 
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Old 03-20-13, 04:39 AM
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by today's standards should all 240 runs be three wire?
You only need two wires and a ground for 240 wiring. Sometimes people confuse a 120/240 circuit (such as a stove) which needs 3 wires and a ground with a 240 circuit (such as a window AC or heater) which only needs two hots and a ground.

just pulled the wire tonight and realized that it was only 12-2 bx wired as 240 to a double pole 20a breaker.
Some say not best practice but in that case you could just remove the white wire from the breaker and move it to the neutral bar and you now have a 120 volt circuit. Best to tag the breaker "Converted to 120 volts" if you do that. You will of course have to change out the receptacle also. (US code only. Canada uses special cable with red and black wires for 240 wiring.)
 
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Old 03-20-13, 06:11 AM
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The cable that you have is using the spiral sheath as the 3rd grounding conductor if it has a bonding strip.
 
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Old 03-20-13, 11:08 PM
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thanks for the clarification

most all of the older homes i have seen wired with bx have their 240 circuits using 2 wires with the metal bx jacket as ground like pcboss mentioned. so for example - if i were running a new 240 circuit today using NM i would only need 10-2 NM with the bare copper grounding wire? in theory why is no neutral required in a 240 circuit?
 
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Old 03-20-13, 11:31 PM
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in theory why is no neutral required in a 240 circuit?
What makes you think it is? It isn't. As Ray explained earlier in this thread,
Originally Posted by Ray2047
You only need two wires and a ground for 240 wiring. Sometimes people confuse a 120/240 circuit (such as a stove) which needs 3 wires and a ground with a 240 circuit (such as a window AC or heater) which only needs two hots and a ground.
 
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