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I currently have a 3 wire running from my panel, red is connected to a 15 amp breaker, black is connected to a separate 15 amp breaker. White is connected to the neutral bus. This is running to a split receptical. I want to install 2 extra outlets. Can I cut the 3 wire, and connect separate 2 wires Black to red and black to black and the connect all neutrals together?

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That is called an Edison circuit I believe. –  iAmNotVeryGoodAtThis Jan 13 '13 at 13:52
    
Your setup is a little dangerous. If you flip just 1 of the breakers, the white can still carry a current. Code today requires that the 2 breakers be bonded, so they both flip off together. Look up "Multi-wire Branch Circuit" (MWBC). –  Jay Bazuzi Jan 13 '13 at 19:36
    
In multi wire/phase systems there is always a hazard when the neutral becomes disconnected or loose. A MWBC adds to that hazard by making more opportunities for a disconnected or loose neutral that will not always be detected as a circuit outage. –  Skaperen Mar 17 '13 at 12:39
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5 Answers

Yes, you should be fine to do this. There's two common configurations:

  • Where both black and red are actually the same feed, but black is always energized and red is controlled by a switch. Normally, you only carry the switched leg up to the single split receptacle, but occasionally you'll see both black and red in every box, allowing any receptacle to be converted to work off the switch. Not really common unless it's a custom rough-in. Just make sure you're actually dealing with two circuits.

  • Dual circuit split receptacles as you describe, top half black, bottom half red (with the bond between them broken), sharing a common neutral. Common in kitchens, bathrooms, work rooms, etc.

The only thing you have to watch out for on a dual circuit setup is the single neutral. Both circuits have to be on different phases otherwise you create something called a multifeed. If you look in your panel, you have two incoming wires landing on the bus bar where the breakers attach. One black, one red - those are your phases. Every breaker going down the line is on a different phase, e.g.:

          (incoming utility feeders)
               |              |
               |              |
       (black) /              \ (red)
             black           black
             red             red
             black           black
             red             red

Make absolutely sure that the three wire conductor landing in the panel is in fact paired black to black and red to red. Two circuits on the same phase can not share the same neutral. You would never attach a three wire conductor to a tandem breaker, as both circuits in the breaker would actually be coming from the same phase, for instance.

Other than that, yes - if you want to 'pigtail' to add additional receptacles you should be fine, and they can share the same neutral (white) wire.

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there isn't any relationship between 3 wire cicuits being peculiar in kitchens. Three wire ckts can be utilized for use in any room in a house & in most commercial applications as well. The implied situation aforementioned by others above, is for 2 seperate 120 volt circuits using a common neutral . Note that both the red & black wires must be on seperate phases & should read 240 volts between them ,or double whatever each black or red read to ground , hence ; if u read 112 volts from black to ground & 112 volts from red to ground u should read 224 volts between the red & black in a single phase service found in most homes. The neutral wire will carry the difference between the amperage found on the black wire & the red wire. For example , if there is 5 amps flowing on the black wire & 5 amps flowing on the red wire the neutral wire or white wire will have zero amps on it , but only if the red & black wires are connected to different phases ! In a scenario whereas the red & black are incorrectly connected to the same phase, with 5 amps on the red & 5 amps on the black the neutral current will be the sums of the black & red wires or 10 amps Consequently, with red & black wires connected incorrectly with 15 amps flowing on the red & 15 amps on the black the neutral will carry 30 amperes. On a #14 wire rated for a max of 15 amps you would have 30 amperes flowing on a 15 amp wire which when overloaded will get hot & possibly cause a fire !

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I up-voted it because it is a fair answer, could you reformat it to be a little easier to read? Some line breaks perhaps. Thanks. –  ShoeMaker Mar 16 '13 at 11:50
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As others have mentioned, this is a shared neutral configuration. Technically, yes you can do it however I believe the current NEC only permits such circuits in a kitchen. The most common use of this is to have an outlet where both top and bottom plugs are on different circuits.

You are also required to have the circuit breakers tied together so if one trips, both are shut off. The most important part of this configuration is that the two hot conductors come from different legs of your service so that they are out-of-phase from each other. The result of this is that they balance out the neutral conductor; if you used hot from the same phase you could double the allowed current over your neutral conductor.

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I agree that the current code requires that the breakers be tied together, but I'm pretty sure there's nothing new about only permitting such configuration in kitchens. Kitchens outlets are required to be served by two 20 amp circuits, and it's better and cheaper to do this with one 12-3 Romex cable (as opposed to 12-2). –  Edwin Jan 13 '13 at 15:40
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Having the circuit breakers tied together also ensures that they are out of phase with each other. If they were somehow on the same phase the neutral conductor could have as much as 30 amps running through it. (assuming two 15A breakers) –  Brad Gilbert Jan 13 '13 at 15:56
    
No, code does not require the breakers to be tied together (those circuits should trip independently), and you can have two circuits anywhere you want. You only need to tie the breakers together if it's a 240V receptacle (or circuit). As far as the neutral goes, as long as the two circuits are on different phases, you're fine, otherwise you create what's called a 'multifeed'. –  Tim Post Mar 16 '13 at 5:17
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Sure. It should be evident to someone who is working on the outlets in the future that this is what you did. The hot wire on the 'red' circuit should be marked red. Use red electrical tape to mark the black wire on the 'red' circuit at both ends.

Another option is just to continue the split receptical setup for the two additional outlets. All you need to do is remove the fin on the hot side of the outlets to split them.

While you are working on these circuits, it might be a good time to install AFCI breakers, if you don't have them already. They can save your life by preventing fires. In my opinion, they should be used all the time when you are running non-metallic cable. Recent code requires them in all areas of a home, except where a GFCI is required (bathrooms, kitchens, garages, etc).

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If I understand your question right, the answer is yes. Treat the red and black as two separate circuits and the whites as a common neutral. Be very careful not to allow the red circuit to contact the black circuit from the original 3 wire source.

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