Is 12-2 w/g NM (Romex) OK for 220V?

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  #1  
Old 11-10-01, 09:37 AM
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techtim
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Question

I am adding some new circuits to my garage for my woodworking tools. All 3 circuits are 20 amp 120v. If I buy 220v equipment in the future, can I use the same wiring (different breaker and outlets of course)? I would take one of the circuits and convert it to 220V 20A. Or should 12-3 be used?

Also, the Romex is leaving the panel in my basement and going through an adjoining crawlspace under the family room to get to the garage. To meet code, can Romex be staple to the bottom of joists (basement and crawlspace), or should holes be drilled in the joist?


Thanks, Tim
 
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Old 11-10-01, 10:23 AM
J
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Yes, Romex can be used for 240 volts.

But will 12-gauge (i.e., 20 amps) be sufficient for your future needs?

And will 12/2 (i.e., pure 240-volt tools) instead of 12/3 (mixed 120/240 volt tools) be sufficient for the future?

The answer is probably yes, but a little research is always a good idea when planning for the future. I recommend that you go window shopping. Find the kinds of tools you might buy in the future and check their power requirements.

In a crawl space, the Romex can be stapled to the bottom of the joists. When running parallel to the joists, it would be better to staple to the sides of the joists.
 
  #3  
Old 11-10-01, 11:17 AM
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techtim
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Thanks for the reply and interest.

Are you saying that if I run 12/3 now, I can simultaneously have 120v and 240v outlets on the same 2 pole breaker? Or if I stick with 12/2 w/grd, I can convert a 120 to 240? I am running enough circuits that it would not hurt to lose a 120 circuit to a 240.

I don't have any 240v tools yet, but I have looked at anything I'm interested in buying. The most draw I could find was on a contractor grade table saw at 9 amps 240v 1.5HP motor.

Tim
 
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Old 11-10-01, 12:30 PM
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No, you can never safely get both 120 volts and 240 volts from the same 12/3 cable without installing a subpanel on that wire. Some appliances can draw both 120 volts and 240 volts from the same cable, but you can't do it yourself in two different appliances. Aside: I'm not sure why this isn't allowed. Can somebody explain the danger if this were to be allowed? Seems like the double-pole breaker would trip if any wire drew excess current, so why not allow it?

If you run 12/2 with ground, you can later convert the entire circuit from 120 volts to 240 volts (if you have an extra slot in your panel).
 
  #5  
Old 11-10-01, 02:15 PM
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resqcapt19
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John,
Where does it say that you can't feed both 120 and 240 volt loads from the same 3 wire circuit connected to a 2 pole breaker? I have installed a number of receptacles where the top part was 120 volt and the lower part was 240 volt. These were fed from a 3 wire 240 volt circuit on a double pole breaker. They were installed in apartment buildings near widows where it was expected that the occupant would be installing window air conditioners. This let the occupant chose either a 120 or a 240 volt unit without requiring any rewiring.
Don(resqcapt19)
 
  #6  
Old 11-11-01, 03:25 AM
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Wgoodrich
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John, resqcapt19 is right the NEC allows you to do exactly that running both 120 and 240 volt appliances from the same 240 volt circiut while using a common neutral. However this wiring design should be done with great care not to intermix this common neutral with a grounded leg of a third circuit. Remember that the neutral carries the unbalanced load. As long as that neutral only carries the unbalanced load of those two hot lines used as a multiwire circuit you can not overload that common neutral. If you installed a 1 amp 120 volt load and then a 19 amp balanced 240 volt load on that multiwire branch circuit the load on the neutral would only be the 1 amp. If you installed a 19 amp load on the 120 volt loads and then a 1 amp load on the 240 volt balanced load then you would be carrying 19 amps on the neutral. You could never overload a white common neutral whether using both 120 volt and 240 volt as long as you did not overload the breaker with the combined 240/120 volt loads applied to tha circuit. Indeed the breaker would trip before any one hot or the neutral became overloaded.

The dangerous part of this wiring activity is the DIYer installing a multiwire circuit and without knowing it tied a grounded leg of a third circuit to that white common neutral thus setting up the ability to overload that common neutral.

The NEC allows a 120/240 volt combined circuit design. Just be sure that the installer knows what he is doing and guards against tying that third grounded leg into that common neutral wire.

Good Luck

Wg
 
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Old 11-11-01, 06:07 AM
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Thanks guys. Another one of the things I thought I knew turns out to be untrue. But it does make more sense, since I couldn't think of a valid safety reason for what I incorrectly thought was a prohibition.
 
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