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# Which wire/marking for 220v circuit

#1
10-07-07, 03:24 PM
Member
Join Date: Jul 2007
Location: Snohomish, WA
Posts: 27
Which wire/marking for 220v circuit

I will be installing a couple of 20A circuits to my shop for my table saw and dust collector. These will both be three wire; hot, hot, ground. So, when I buy nm sheathed cable, do I buy 10/2 w/ ground and mark the white wire black, or do I buy 10/3 w/ ground and leave the white wire unused? I'm guessing the first answer is correct, but in case it is the second, do I just roll up the white wire at both ends and leave it in the box or panel?

#2
10-07-07, 06:00 PM
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Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
You can do either method. If the circuits are and will always be straight 240 volt circuits (or perhaps be changed to 120 volt circuits) then two conductor plus ground cable is fine.

However, if there is any possibility that the circuits will someday be 120/240 or if you might want to convert them to a multi-wire circuit then use three conductor plus ground cable. If you use three conductor cable, then leave the extra wire (the white one) unconnected but out of the way on both ends.

Why are you using 10 gage wire? 12 gage is fine for 20 amps. is the distance significant? Are you planning ahead in case either needs to be 30 amps in the future?

#3
10-08-07, 06:23 AM
Member
Join Date: Jul 2007
Location: Snohomish, WA
Posts: 27
Yes, 12 gauge is probably OK. It is about a 100 foot run, so distance is an issue. When I ran it through the wire calculator on Southwire, I was pretty close to the 3% drop, so I was thinking go with the larger wire. When I see the price difference at the store, though, I might change my mind. Thank you for your thoughts.

#4
10-08-07, 06:30 AM
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Join Date: Sep 2003
Location: Central New York State
Posts: 13,973
When you used the coltage drop calculator, did you use the full 20 amps, or did you use the real value for the tool?

You might want to consider a sub panel for your shop. If you bit the bullet now and spend some more money you can install a sub panel that will allow for future expansion to be done later, which will be easier from a sub panel.

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