Running new circuits, is 12/3 cable OK to save runs?

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On 10/4/2010 7:14 AM, George wrote:

ok, go ahead and try that.
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Steve Barker
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GFCI receptacles only require a dedicated neutral downstream of the receptacle (on the load side), you can feed them with a shared neutral no problem.
Cheers, Wayne
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On 10/4/2010 8:59 AM, Wayne Whitney wrote:

ok, that clears that up. what i did is run 12/3 from box to box to box, and alternated using the red and black. In this case, i have to use a gfci at each and every box.
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wrote:

Personally, I prefer using GFCI receptacles at each and every box, but you could have used a double pole GFCI breaker, then alternated with standard outlets
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On 10/4/2010 4:40 PM, RBM wrote:

the load side it would trip the gfci, OR that if there was a trip, it would trip both legs or something to that effect. I've never actually finished my project, so i don't know. I actually wasn't planning on putting any gfci's on there at all, so i rekon it really doesn't matter. <G>
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On 10/4/2010 9:30 AM, Steve Barker wrote:

Works fine. Draw the circuit out on the back of an envelope. The GFCI works by looking at the differential in the current of the neutral and the hot leg of its internal outlet and any downstream outlets. If the GFCI is downstream from the shared neutral that neutral under normal operating conditions is carrying the same current as the hot leg. Same is true of the GFCI (if used) on the other leg.
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On 10/4/2010 5:40 PM, George wrote:

ok but it sounds like i have to have BOTH the gfci's broke out of the shared common at the same point. so i couldn't have one in one box, and the next in the next box down eh?
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No, you can do that, you just need to split the mwbc into two circuits at your first box. The GFCI in box 1 protects the first circuit; the GFCI in box 2 protects the second circuit, and all the other recepatcles can be normal receptacles. You feed each GFCI with the shared neutral and one of the two hot legs; and then for downstream receptacles, you feed them from the GFCI load terminals and keep the neutrals separate.
Cheers, Wayne
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On 10/4/2010 10:33 PM, Wayne Whitney wrote:

Understood. But my wire is already in place. <G>
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For a kitchen, where AFCI circuits are not required it is perfectly acceptable to do what you propose. You do have to connect them to double pole breakers, so both circuits are opened simultaneously.
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RBM is right on point. Another advantage to the multiwire circuit (what you call this) is reduced voltage drop. The only thing you have to do is split out two neutrals at the kitchen end so you can hook up the GFCIs. You will need a big box for that. I usually gang both GFCIs in a deep 4x4 box there so you have 4 outlets and then go to the down stream outlets from there. On a counter, you never seem to have enough outlets so I like quads all the way down, at least in the places that will accumulate appliances.
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The requirement for double pole breakers only applies if both of the ungrounded current carrying conductors terminate on the same strap or yoke. Passing through the same box is not sufficient reason to invoke that rule. There is no problem with the required GFCIs for the counter top receptacles because you only use the 12/3WG for the home run. Once you get to the first kitchen counter top box you split the circuit down to runs of 12/2WG from the first GFCI to the remaining receptacles on that side of the multiwire branch circuit. Likewise for the Microwave/Range hood and refrigerator circuit; which need not be twenty amperes and therefore twelve gauge wire; you can run 14/3WG to whichever box is closer to the panel in wire feet and run 14/2WG from there to the other outlet. That technique recommends itself to the food waste disposer and dish washer loads as well.
[RANT MODE] As for the fella or gal coming along ten years from now if they don't know how to use a tester to assure that all circuits in a box that they are going to work in are deenergized or understand the necessity to keep the two ungrounded conductors on the opposite legs of the panel THEY SHOULD KEEP THEIR UNEDUCATED HANDS OUT OF ELECTRICAL WORK. I will never be willing to try to dumb down electrical work in a futile attempt to make it safe for untrained persons to do the work because I know that it cannot be dumbed down that far. Electricity can kill! Understand it, respect it, or leave it the hell alone! [/ RANT MODE]
-- Tom Horne
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Right, but new in the 2008 NEC is a requirement for simultaneous disconnect for all ungrounded conductors of a multi-wire branch circuit, so at least a handle-tie is required.
Cheers, Wayne
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The requirement for double pole breakers only applies if both of the ungrounded current carrying conductors terminate on the same strap or yoke. Passing through the same box is not sufficient reason to invoke that rule. There is no problem with the required GFCIs for the counter top receptacles because you only use the 12/3WG for the home run. Once you get to the first kitchen counter top box you split the circuit down to runs of 12/2WG from the first GFCI to the remaining receptacles on that side of the multiwire branch circuit. Likewise for the Microwave/Range hood and refrigerator circuit; which need not be twenty amperes and therefore twelve gauge wire; you can run 14/3WG to whichever box is closer to the panel in wire feet and run 14/2WG from there to the other outlet. That technique recommends itself to the food waste disposer and dish washer loads as well.
[RANT MODE] As for the fella or gal coming along ten years from now if they don't know how to use a tester to assure that all circuits in a box that they are going to work in are deenergized or understand the necessity to keep the two ungrounded conductors on the opposite legs of the panel THEY SHOULD KEEP THEIR UNEDUCATED HANDS OUT OF ELECTRICAL WORK. I will never be willing to try to dumb down electrical work in a futile attempt to make it safe for untrained persons to do the work because I know that it cannot be dumbed down that far. Electricity can kill! Understand it, respect it, or leave it the hell alone! [/ RANT MODE]
210.4 has changed , and now requires simultaneous disconnect of all ungrounded conductors regardless of how or where they terminate.
I wholeheartedly agree with your rant.
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Microwave/range hoods use a lot of power. Mine uses 1500 watts. Should that have it's own neutral? We put ours on a single 14/2
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On 10/3/2010 8:20 PM, Mikepier wrote:

run, but not how long. If it is really long, a sub panel might be the answer to keep voltage drop down. It might make sense, especially if there are other possible additions in the future.
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By my count you have 3 circuits. Are 2 circuits for the counter top required by code now?
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That is what I meant above. 2 seperate circuits for 2 counter outlets. I was told this is code.
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On 10/4/2010 8:19 AM, jamesgangnc wrote:

have been for many a year.
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Steve Barker
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It is allowed, and it will give you a slightly better performing installation than running the 4-12/2 cables. [Less voltage drop, less use of resources (copper), marginally smaller holes in the floor joists.] However, as you can see from the variety of responses, it is also confusing to many people, so that may be an issue.
The only downside is that you will need to use a double pole breaker or a handle tie with two single pole breakers on opposite phases. Once you arrive at your destination, you can split the 12/3 into two separate 12/2 circuits as desired. This will in fact be necessary downstream of any GFCI receptacles.
Cheers, Wayne
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