Can I use half of a 2-pole breaker?

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  #1  
Old 05-28-13, 08:09 AM
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Question Can I use half of a 2-pole breaker?

So here's the situation. I'm putting a 60amp subpanel out in my shop. All we need in the shop is 120, so I just ran 3 wires from the house to the shop, my hot, my white, and my ground (I know this is unusual, and that most people run 240 in case they need it later, but I was short on funds so...) I want to be able to run 4 15amp circuits at once in the shop. So in order to do that I'd need a 60amp breaker in the house panel. However, the problem is that the largest single pole breakers that are made for my panel are 40amp.

So here's my question:Can I use one half of a 2 pole breaker? And if I can what size would I use - 120amp, or 60amp to get the 60 amps I need.

I asked someone I know about this and he said something about it taking twice as much to trip the breaker...would this be an issue?

Thanks,

Ian
 
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  #2  
Old 05-28-13, 08:44 AM
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Without commenting on your installation there you would use a 60 amp breaker. Using one side of a two pole circuit breaker would work but it is not proper.
 
  #3  
Old 05-28-13, 09:26 AM
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(4) 15 amp breakers in the shop subpanel shouldn't require a 60A main. You say you want to use all 4 circuits concurrently, but for what use. Certainly they would not be at maximum capacity. I'm guessing a 30A single pole would be fine, but perhaps someone else can give you a better number with more info.
 
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Old 05-28-13, 09:34 AM
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Yes, they may not all be using 15amps at once, but it's possible. For instance, one circuit is basically taken up by all the fluorescent lights I have going. And then two others could easily be taken up by two 13-15amp machines running concurrently (band saw and table saw for example). The 4th I probably won't use now, but want just in case we need it later.
 
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Old 05-28-13, 09:47 AM
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If the full load amps are that close to 15 amps then they should be 20 amps with #12 wire.

You are actually making this more expensive for yourself then it needs to be. For 60 amps you need #6 wire but you would have had more than enough power if you had run four #10s off a 30 amp two pole breaker or maybe four #8s off a 40 amp two pole breaker.
 
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Old 05-28-13, 09:58 AM
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Can I use one half of a 2 pole breaker?
No. The breaker must be able to trip before the wires connected to it can become damaged. A 2-pole breaker only loaded on one half is likely to have too much mechanical resistance to do that.

Either run a 4-wire 240V supply or use a single-pole breaker.
 
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Old 05-28-13, 12:21 PM
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"before the wires connected to it can become damaged"

Does this mean that in theory as long the wires were a large enough gauge it could work?
 
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Old 05-28-13, 12:32 PM
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Does this mean that in theory as long the wires were a large enough gauge it could work?
No. Only wires of the proper gauge should be connected to any breaker.

OK, longer answer: The breaker must be able to trip before the wires connected to it can become overheated or, if a fault occurs, before that fault can cause any harm or damage.

I regret not giving the longer answer earlier.

Originally Posted by Nashkat1
Either run a 4-wire 240V supply or use a single-pole breaker.
Is there some reason you don't want to do either of these?
 
  #9  
Old 05-28-13, 12:42 PM
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Thanks, and the reason is that I don't get quite what I want with either of them, but that's ok. Will just go with the single pole option I think.

As for the other I'm more just curious at this point if there is any situation in which it would be safe to run wire into one side only of a 2-pole breaker?
 
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Old 05-28-13, 02:15 PM
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the reason is that I don't get quite what I want with either of them,
A good point. What is it that you want?

As for the other I'm more just curious at this point if there is any situation in which it would be safe to run wire into one side only of a 2-pole breaker?
No, there isn't, for the reason I stated earlier.
 
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Old 05-28-13, 02:33 PM
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What size wire or cable were you planing to use?
 
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Old 05-28-13, 06:58 PM
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Although I would run a 120/240 volt feeder, you could run a 120 volt feeder protected by a 50 amp single pole breaker. A 50 amp breaker will easily handle the load on 4 - 15 amp circuits. I don't think you'll find a 60 amp single pole breaker.
 
  #13  
Old 05-29-13, 06:36 AM
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The breaker must be able to trip before the wires connected to it can become damaged. A 2-pole breaker only loaded on one half is likely to have too much mechanical resistance to do that.
If that's the case then all the MWBCs on 2-pole breakers are accidents waiting to happen.
 
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Old 05-29-13, 09:07 AM
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If that's the case then all the MWBCs on 2-pole breakers are accidents waiting to happen.
That's why a MWBC should be supplied from two single pole breakers with their handles joined with a handle tie.

"Independent trip, common disconnect."
 
  #15  
Old 05-29-13, 10:56 AM
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It would also mean that an unbalanced overcurrent condition in say a subpanel would mean meltdown rather than trip. Nawww. You want to stamp "UL" on that?
 
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Old 05-29-13, 11:17 AM
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Nashkat, a 2-pole breaker does not trip through the handle. There is a small piece of plastic that connects the trip mechanisms. If that was the case, you could pull an infinite amount of current on one leg through a subpanel as long as the other leg remains less than the rated current of the OCPD.
 
  #17  
Old 05-29-13, 11:31 AM
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If you say so, Justin. The NEC requires the simultaneous disconnect and, I think, recommends the independent trip for a MWBC.
 
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Old 05-29-13, 05:33 PM
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In the case of single phase multiwire branch circuits, the NEC requires either a 2 pole breaker or two single pole breakers with a handle tie. I don't believe the NEC expresses a preference.

http://www.mjobee.com/projects&news/...rt%20210.4.pdf
 
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