Ktchen Appliance outlets on 12-3 wire

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  #1  
Old 12-28-05, 12:19 PM
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Ktchen Appliance outlets on 12-3 wire

I read somewhere that I can run my two kitchen appliance circuits on a single run of 12-3 cable using red and black as the hot with a single neutral. This makes it easy to alternate between the two circuits on a single cable. Is this a standard practice?

I would either have to run two two-wire cables from the subpanel to my GFCIs and then marry the two circuits into one three wire cable OR run a three wire from the subpanel first to one GFCI and then the other and then on to all the appliance outlets alternating the circuits that get hooked up. Either way it doesn't seem right to have hot power from two different circuits in a single cable.

I'm not really looking for shortcuts, it's just simpler to run a single cable.

Thanks,

Steve
 
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Old 12-28-05, 01:05 PM
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Yes, two 20 amp small-appliance circuits connected to a 3-wire Branch-Circuit cable is indeed "common practice"

But what you must do, at ALL outlet-box connections with 2 or more White wires, is to connect ALL White wires together with a White wire "device-lead", so that the ONLY Neutral (White wire) connection between the receptacle terminal and the White wires of the Branch-circuit cables is via the "device-lead".

You will note that when the device-lead is dis-connected from the receptacle terminal, it DOES NOT open the circuit; the only "break" is at the terminal of the receptacle.

Good Luck, & Learn & Enjoy from the Experience!!!!!!!11
 
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Old 12-28-05, 01:47 PM
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Let me make sure I understand. What you're saying is that I have to wire a pigtail to the two other neutrals in the box (one entering and one leaving) and connect that to the neutral connection on the socket. I'll have to do that for the hot wires as well. I can get behind that.

How do the circuits get fed from the subpanel? Is that done with a single three wire cable (meaning I'll have a red wire in the sub panel) or is it done with two two-wire cables running to the GFCIs which then get spliced to the three wire cable?

Thanks. I'm learning a lot. After this remodel, if I lose my job, I'll be able to reinvent myself as a contractor.

Steve
 
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Old 12-28-05, 01:48 PM
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Bob, what you are describing is a multi-wire branch circuit. These are a standard technique, however they are more complex and there are a few ways that they can 'gotcha'. Basically, you end up with something that can supply the power of two circuits, but is actually a single interconnected circuit. Code will sometimes treat a multi-wire circuit as a single circuit, and elsewhere treat it as multiple circuits, and it can be hard to keep the requirements straight. If you wire a multi-wire circuit incorrectly, then you will overload the neutral and cause a fire hazard. In general, we advise people to stay away from multi-wire circuits on DIY projects, because of the additional complexity.

For your application, I'd suggest that you look into getting 12-2-2 wire. This is a single cable with _4_ circuit conductors plus ground; a black 'hot' wire with its corresponding white neutral wire, and a red 'hot' wire with a corresponding white with red stripe neutral wire. Two electrically separate circuits, neatly packaged in a single cable.

If you are interested in going with a multi-wire circuit, you will need to do a bunch of reading on the subject. An internet search for "multi-wire branch circuit" should give you enough to get started.

Multi-wire branch circuits do not play well with GFCIs. You _cannot_ use multiwire techniques on the load side of a GFCI; because of the way that GFCIs work, they will detect the multiwire loads as ground faults and trip. GFCIs can be _fed_ on the line side with multiwire circuits. If you decide to use multi-wire techniques to feed the receptacles, then you will need separate GFCIs for each receptacle.

One fairly common technique is to use a multiwire circuit to feed the first GFCIs, and then to use ordinary wiring on the load side of the GFCIs. This provides the two kitchen counter receptacle circuits with a single cable back to the panel.

-Jon
 
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Old 12-28-05, 03:27 PM
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Okay, did some reading about multi-wire branch circuits. It seems that the two circuits should be fed from different phases so that the neutral only carries the difference between the two circuits. That way if one of the circuits is shut off the neutral then carries the full load of the remaining circuit. That being the case, I should then be able to run a three wire cable from the subpanel to the first GFCI and connect the black and neutral to it and pass through the red. Then at the next GFCI connect the red and neutral to the GFCI and pass through the black. The outlets following the GFCIs (and protected by them) would all be wired the same way, using the single neutral and alternating the hots. Would a ground fault on one circuit then trip both GFCIs? Would there be any other problems with the GFCIs?

This is really the only circuit I plan on doing this with and just want to make sure I do it right. I am just as much about learning as I am about saving time so this thing kinda interests me.

Steve

OOPS, just re-read the last post. I guess I would need a bunch of GFCIs in the kitchen where I was planning on only using two. The extra cost of 6 GFCIs over regular outles, in my mind anyway, overshadows the benefits of doing this, for the kitchen anyway. I may feed the GFCIs doing this, though. Thanks for the info.
 
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Old 12-28-05, 10:48 PM
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A danger of the three wire circuit is that the voltage across the two hot wires is 240 volts. You should be sure to only tap only one of the hot wires in each box and pass the other through. You should use a two pole breaker in the panel, so that tripping one hot or shutting off the breaker will kill all power to that cable and circuit.
No matter which two adjacent positions that you place a two pole 240 volt breaker onto, in the service panel, you will be connecting each wire on that breaker to opposite hot legs of the service to the house (which is 240 volts across them). The two legs are 180 out of phase so that when one is peaking its max voltage in the plus direction, the other leg is peaking in the negative direction. These will cancel each other out when they travel down the neutral wire, allowing us to use one neutral for two hot wires.
This is a rather simplified explaination.
Look at the difference in cost for X feet of 12/3 vs. 2X feet of 12/2 NMB cable.
I agree with Winnie that a DIY should not use this type of circuit unless they really understand electricity and what they are doing. They have a higher "gotcha" factor.
 
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Old 12-29-05, 04:51 AM
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Just to be clear, so that if you discuss this project with anyone else: using a two pole breaker for a multi-wire circuit is _not_ required by code, and you might be told that you don't need one. Using a two pole breaker is, however, a _very_ good idea, and my _strong_ suggestion for any DIY work using multi-wire circuits.

A two pole 240V breaker will guarantee that the circuit is supplied by opposite legs of the supply, and also protects from stupid mistakes involving the neutral when you work on this circuit.

Keep in mind that this must be a proper 240V two pole breaker, not a 'skinny' twin breaker used to get extra circuits in a panel. The skinny breakers fit two breakers in the space of one, and place both breakers on the _same_ leg of the supply, exactly what you don't want to do!

-Jon
 
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Old 12-29-05, 05:43 PM
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An Idea is to bring the 1/3 multiwire cable to your kitchen, and run separate 12/2s from it, or a 12-2-2.
 
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