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

[Wayne Whitney]

That is correct. I didn't bring it up because as you noted it only affects installation of 5 or more bundled 12/2s.

Cheers, Wayne

[RBM]

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.

[HerHusband]

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

[Bob]

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.

[John Gilmer]

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.

[Wayne Whitney]

I believe that only occurs in 3-phase MWBCs, not 1-phase MWBCs

Cheers, Wayne

[trader4]

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.