Question on repurposing a circuit

5 years ago

I need a circuit for the shop in my garage for a table saw that requires 240 V, a 30 amp double pole breaker, and a 10/2 w/ ground cable. Looking in the breaker box, I remembered that I have a no-longer-used 10/3 w/ground cable already in the box connected to a 30 amp double pole breaker. This used to run all the way to the kitchen to a box under the electric stove, but I disconnected and capped all the wires in the box years ago when we installed a gas range, but didn't disconnect them at the breaker end. My thought is to throw the main breaker, detach and cap the unneeded white wire for this cable that goes to the neutral bus bar, go into the open attic over the garage and cut the cable so I can run it to a new receptacle box. Then I would install a 240 V receptacle using the red, black and ground, and cap the unneeded white wire in the box. Is this approach to dealing with the unneeded third wire code compliant, or do I have to run a whole, new 10/2 w/ground cable?

Featured Answer

Ron Natalie

5 years ago

Stoves were common consumers of 120/240. They'd use 240 for the heating but 120 for the light bulb(s) and sometimes accessory receptacles.

Yep, a 30A subpanel will be limited, but most table saws don't pull 30A. Even most 3HP saws run fine on 240 on a 20A circuit. If you're willing to concede you're not going to run a lot of other loads at the same time, you should be OK. Most single person shops get by like that (as long as you're not running something like a space heater or fan continuously on the shared feed).

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Comments (10)

greg_2015
5 years ago
It's fine.

In fact, if you are going to run 10/3 from where you cut it in the attic to the new box, I'd even leave the white wire attached to the neutral bus bar in the breaker box and just cap the white in the box where you will install the 240V receptacle.

That way, if anyone ever needs a 120/240v receptacle there, they can just switch it out without doing anything at the breaker box.
kudzu9 thanked greg_2015
kudzu9
Original Author
5 years ago
last modified: 5 years ago
Greg-

That's an interesting idea. So if I also wanted a 120 V receptacle, I could just mount it on the same receptacle box as the 240 V receptacle, connect the white wire to the neutral terminal, pigtail either the red or black to the hot side, and pigtail a ground to it? Or would it be best to use a separate box for the 120 V receptacle and just run a short, separate cable between the two?

Lastly, is there any code issue with having a 120 V receptacle on one leg of a double pole breaker that is 30 amps? I thought standard 120 V receptacles were only rated to 20 amps.
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greg_2015
5 years ago
As you said in your last part, regular 120V receptacles are only allowed on 15A or 20A circuits.

I was thinking more along the lines of a dedicated piece of equipment that might require 120/240V like a clothes dryer or a stove. I don't know if electric chargers for cars are all purely 240v or if some are 120/240v. Maybe there's some other item that could require that.

I guess the likelyhood of needing a 120/240v circuit there is probably pretty slim, but since it's extra effort to disconnect the neutral wire, there's no real point in doing it.
kudzu9 thanked greg_2015
Ron Natalie
5 years ago
last modified: 5 years ago
The first part is fine (pulling the existing 10-3 to the table saw and ignoring the neutral).

What you can not do is put 15A or 20A receptacles on a 30A circuit. Not permitted (for good reason) whether there is anything else on that circuit or not.
kudzu9 thanked Ron Natalie
kudzu9
Original Author
5 years ago
Greg-

Thanks, again. I could use more 120 V circuits in my garage, so that was why I was following up. In any case, I'll follow your suggestion to leave the neutral attached in the breaker box. I'm pretty knowledgeable about electrical work and safety, but not having to mess around in the breaker box is a good thing.
Ron Natalie
5 years ago
What you could do is put a small subpanel in and pluck off branch circuits for whatever you like. The problem is that you'll trip the breaker on the feeder if you use too much at once, but it's neither unsafe nor against code.
kudzu9 thanked Ron Natalie
Bruce in Northern Virginia
5 years ago
AFAIK, the 120/240 volt configuration is part of the design of some appliances and it is usually for something like a 120 volt clock on a 240 volt stove.

Installing a subpanel would give you more flexibility, although the subpanel would be limited to 30 amps if you use 10/3.

Bruce
kudzu9 thanked Bruce in Northern Virginia
mtvhike
5 years ago
last modified: 5 years ago
Ron, could you put a 30A subpanel with a few separate breakers, one 30A/240V for the saw and a couple of 15A or 20A 120V ones for auxiliary circuits? Of course, your breaker in the house would also be 30A and you couldn't run everything at the same time.
Ron Natalie
5 years ago
Yep. That is allowed. There's no requirement that the feed or service has to equal the sum of the breakers.
kudzu9 thanked Ron Natalie