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

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You'll need to run dedicated circuits for:
1. Refrigerator 2. Microwave 3. Dishwasher 4. Kitchen Outlets (odd) 5. Kitchen Outlets (even) 6. Kitchen Lighting 7. Range 8. Wall Ovens that are not built-in to the range 9. Garbage Disposal
If the range hood is not part of the microwave, it can be placed on the lighting circuit (not the outlet circuit).
The kitchen outlets need to be GFCI protected, either with dedicated breakers, or by using GFCI recepticles as the first outlet in the run. Ideally, you should run two individual 12/2 cables. While I "think" a shared neutral in 12/3 is allowed in this case, it doesn't cost that much to run a second 12/2 cable. If you go with a shared neutral, you'll need to ensure the circuits are "balanced" in the breaker panel (off each side of the 240 supply) and the breakers tied together with a bar. Keep in mind if you have a problem with one of the shared circuits in the future, or if you end up doing some kind of remodeling, you'll have to shut down ALL kitchen outlets. Keeping the two circuits isolated allows you to shut down only the circuit you are working on.
By the way, the kitchen outlets should be spaced no more than 4' apart, alternating circuits along the run (I spaced ours every 32"). The idea is to balance the load if you have a toaster plugged in one outlet and a coffee maker in the next outlet.
Anthony
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On 10/5/2010 9:34 AM, HerHusband wrote:

dedicated circuits for 1, 2, 3, and 9 are not REQUIRED, but handy. Just a clarification.
Garbage disposer and dishwasher can easily be on one circuit.
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Steve Barker
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Steve,

Hmm... I guess you're right. I read NEC 210.52B1x2, and missed the first part allowing the refrigerator to be on the small appliance circuit.
However, I used to service microwave ovens and it was very common to find tripped breakers if the microwave had been used while the refrigerator was running. Granted, they were probably only 15A circuits in older houses, but it just seems wise to me to dedicate a circuit to any major appliance.
My rule of thumb when we built our house (2003), if you don't unplug it and put it away, put it on a dedicated circuit.

I think it depends on the electrical requirements of the disposer (430.53A?). While it might be OK with the current disposer, who's to say someone won't replace it with a more powerful one in the future. It's easy enough to run two circuits, why not.
Anthony
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On 10/5/2010 20:29, HerHusband wrote:

Another common remodeling blunder is to replace the range hood with a built-in microwave and connect it to the same circuit as the old exhaust fan. As was previously stated, the fan cannot be on one of the small appliance circuits. Typically it's on the lighting circuit.
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I take it you mean to power half of your outlets from one "side" of the 120/240 service and the other half from the other side.
Generally speaking, that's OK.
Potential problems:
1) You have to use a 2 pole breaker for each of your circuits. 2) You may not be able to find "special" breakers (arc fault, GFCI) in the 240 (+ neutral) style. 3) The savings come from the fact that the neutral currents from the two complementary circuits tend to cancel. But some harmonics (like you might see with flourescent lighting and microwave ovens) re-inforce each other. In practice since most of the neutral currents cancel, the relatively small amount that reinforces (i.e.: the neutral will carry MORE current than the "phase" conductor) shouldn't be a problem.
It's an especially good idea if you have "heating" loads such as toasters. They don't generate harmonics.
You should install GFCI outlets individually (rather than using one GFCI outlet to protect "downstream") and use a pigtail from the common neutral rather than "wiring through" the outlet. An open neutral can cause MAJOR problems.
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I believe that only occurs in 3-phase MWBCs, not 1-phase MWBCs
Cheers, Wayne
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Arc fault is not required in a kitchen. 2 pole GFCI breakers are readily available and not hard to find. However they are usually considerably more expensive than two single pole GFCI breakers, which could be a factor and negate some or all of the savings in wire. But he could also use two GFCIs in the kitchen for each circuit instead.

I don't see how in the world this could ever be a consideration in a shared neutral circuit in a residential application. You'd have to have a huge phase shift in a significant portion of the current for that to be a consideration. I don't know of any such loads that are intended to be plugged into a kitchen outlet.

He can use a GFCI breaker or he can install one GFCI at the first outlet in each half of the circuit and that will protect the downstream outlets. There isn't anything different about a shared neutral circuit that requires individual GFCIs.
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