Using one 12/3 to set up two dedicated outlets


  #1  
Old 12-20-04, 12:02 AM
jsforrest
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Using one 12/3 to set up two dedicated outlets

I am working on taking some heat off a badly overloaded kitchen circuit (actually, it serves half the house!). As part of this effort, I ran some 12/3 from the breaker box with the intent of using it to create two new curcuits that would be for "dedicated lines" for the microwave and refrigerator. My questions are:

1) Is there any problem in using one receptical for both my curcuits (ie: the top plug for the microwave circuit and the bottom for the fridge)? My plan is to break the tabs, use black as the top hot wire, red as the bottom hot wire, and pigtail both the exiting white wires to the white wire in my 12/3.

2) Do I need to use a double pole breaker for this kind of arrangment? Or can I just use two single pole breakers?

Thanks!
 
  #2  
Old 12-20-04, 12:11 AM
J
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Don't think you can use the same nuetral for 2 circuits, but John can answer alot more accurately than I can. But I do know (almost) for sure, that your kitchen should be on its own circuit, not running half the house. Which I realize takes time, and that's what you're doing, just wanted you to know the extent you should take your idea to be code compliant.
 
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Old 12-20-04, 04:39 AM
R
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You can use the shared neutral for both halves of a duplex receptacle. This is called a multi wire circuit. The key to multi wire circuit being safe is that the two hot wires must be on separate halves of the incoming power. Many people do this with a 240 volt breaker. This assures that you get the proper power, and avoids someone moving the breaker in the future.

However, you have a problem. This sounds like a kitchen. Is this a counter top receptacle? If so it must be GFCI protected. Even if it is not a counter top receptacle, the microwave probably should still be GFCI protected.

For ease of installation, I would install two separate circuits. If you insist on a multi wire circuit, I would install two separate receptacles, either in two boxes or in a double gang box. I would make the microwave GFCI protected.
 
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Old 12-20-04, 04:45 AM
W
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If a 20A circuit feeds a _single_ dedicated receptacle, then it must be a 20A receptacle.

If a multiwire circuit feeds a _single_ 'device', eg. a duplex receptacle with the tab removed, then you are _required_ to use a double pole breaker. If you feed separate receptacles, then a double pole breaker is not required, but as Bob said, it is not a bad idea.

In residential kitchens, GFCI's are not required for fixed appliances. It couldn't hurt to have a GFCI for the microwave. I would advise against a GFCI for the fridge.

-Jon
 
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Old 12-20-04, 06:43 AM
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Originally Posted by racraft
You can use the shared neutral for both halves of a duplex receptacle. This is called a multi wire circuit. The key to multi wire circuit being safe is that the two hot wires must be on separate halves of the incoming power. Many people do this with a 240 volt breaker. This assures that you get the proper power, and avoids someone moving the breaker in the future.

Bob:

Is there any case where a multiwire circuit *cannot* be ran from a 240 volt breaker? I had been staying away from multiwire because of the potential for accidentally connecting both halfs to the same buss. Using 240 volt breakers would certainly prevent this confusion.

I had assumed using a 240 volt breaker would not be allowed (key word: assumed) since it would be feeding two sets of 120 volt outlets. So I was totaly wrong, eh?
 
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Old 12-20-04, 08:31 AM
J
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You Must run shared neutral circuits from a 240 volt breaker. If you don't then the current in the adds instead of subtracts between the 2 hots. You could have 30 amps flowing on the neutral wire and not trip the breaker..
 
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Old 12-20-04, 08:54 AM
W
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Joed, you are slightly in error.

For multiwire circuits, the only requirement is that each hot wire ('ungrounded conductor') be fed from a different leg (phase). In general you are not required to use a double pole breaker.

If both circuits feed the same _device_, then a double pole breaker is required.

Many of us believe that it is a good idea to use a double pole breaker in this application, because it _forces_ each hot wire to a different supply leg. But doing this exceeds code requirements.

chirkware,
I cannot think of any code issue that would prevent using a double pole breaker for a multiwire circuit in a residential application. You will have a design issue, since double pole breakers are 'common trip'; if one circuit overloads then the other will trip out as well.

-Jon
 
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Old 12-20-04, 09:56 AM
J
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There there has been a history of general reluctance among many of the experienced advisors in this forum to recommend multi-wire circuits. The most cited reason is the potential for confusion. A future homeowner may come along and think it is a true 240 volt circuit and do something scary based on his incorrect assumption.

But if you do this and you're very clear on how it is done correctly, I agree that a 2-pole breaker is smart. True if one circuit trips it takes the other one out. But a 2-pole breaker ensures that both hot conductors in that common MN cable are dead when the breaker is turned off for repair or future additions or modifications.

Juice
 
  #9  
Old 12-20-04, 11:59 AM
jsforrest
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Thanks to all for the great info!

Since the outlet is high on the wall and will be behind the fridge, I think I'll use the non-GFI receptical for now, but I'll add a double gang box and GFI for the microwave after I get some of the bigger problemes straightened out.

I also think Ill go with the double breaker. I don't want anyone getting hurt ten years from now. It's such a simple setup because they are both dedicated lines, so even if I lose both for a time it shouldn't be a big issues.

My local store has a breaker setup with two slim 20 amp breakers on the sides and a one double pole 40 amp breaker with a common trip in the middle. This would allow the addition of a double breaker without having to give up a slot in my box. Are these things tried-and-true?

Thanks again.
 
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Old 12-20-04, 12:24 PM
W
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jsforrest,

What you are describing are 'skinny' or 'twin' breakers. If they are made for your panel, then they are fine. However there are several caveats that I can think of.

1) Some panels are only designed for a limited number of the skinny breakers. They will only fit in particular slots of some panels.
2) Just because a breaker seems to fit in your panel, do not assume that it is okay to use that breaker. You must either use a breaker type that is 'listed' for that panel (look at the panel label for these types), or you must use a breaker that has been 'classified' as a suitable replacement for your panel (go the the breaker mfg. web site to find this data).
3) If you use a 'twin' breaker, then adjacent breakers may now on the _same_ pole of your supply. In particular, skinny 'double' breakers usually end up with both breakers on the same supply leg. If you have a skinny 'quad' breaker (4 breakers taking up 2 slots), then this should work fine, but is potentially confusing.
4) If you use a skinny quad breaker with a 40A double pole breaker in the middle, make sure you use it to replace a 40A double pole breaker

-Jon
 
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Old 12-20-04, 12:35 PM
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Originally Posted by JuiceHead
But if you do this and you're very clear on how it is done correctly, I agree that a 2-pole breaker is smart. True if one circuit trips it takes the other one out. But a 2-pole breaker ensures that both hot conductors in that common MN cable are dead when the breaker is turned off for repair or future additions or modifications.
VERY good point. I was VERY reluctant about using multiwire circuits because of potential for future confusion at the breaker box. The 240V breaker eliminates that, and provides SAFETY for the person who just checks the top half of the outlet for juice, not realizing the bottom half has a separate feed


I would try to be VERY clear in labeling EXACTLY what this 240V breaker is for, to avoid future confusion.

I am now VERY much considering using multiwire circuits with my upcoming remodel. To me, tripping both "circuits" (from what others have said, its really one circuit) is a small price to pay. Chances are, the two circuits are close in proximity, so its not like the microwave blowing the circuit is going to shut off your computer. If it does, you probably did something with the multiwire circuit you shouldn't have.

Originally Posted by jsforrest
My local store has a breaker setup with two slim 20 amp breakers on the sides and a one double pole 40 amp breaker with a common trip in the middle. This would allow the addition of a double breaker without having to give up a slot in my box. Are these things tried-and-true?
My breaker box has a similar breaker (a "quad" breaker) made my Murray. In my case, it provides for two 30AMP 240 volt circuits (middle two and outer two are common trips). I saw a 20 and 30 AMP quad breaker on Lowes web site, which could give you a multiwire 20, and a 30 for a washing machine, water heater, etc.

I haven't seen 20/20 quads, which would be handy for multiwire circuit use. My subpanel I will be installing in an upcoming project is a 100 amp 6 space, 12 circuit (CTL) Square D Homeline box, which brings to mind the question:

Anybody know if Square D has quad breakers for the Homeline breaker boxes? I've not seen any myself.
 
  #12  
Old 12-20-04, 11:16 PM
jsforrest
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Originally Posted by chirkware
Anybody know if Square D has quad breakers for the Homeline breaker boxes? I've not seen any myself.

Actually, my box takes the HOME breakers by Square D and my local wherehouse type store carries a full line of breakers with a double pole sandwiched between two 1/2 width single poles (the whole arrangment taking up two spaces in the box).
 
 

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