Running Parallel Circuits

[PastorPaul]

Since this didn't get answered as a post at the end of another topic, I'll run it as a fresh topic and see if the fish bite:

I plan to rewire the garage/shop, putting two 120v duplex receptacles at each work station. I had planned to use 12-3 with ground, with each one of the hots feeding one of the two receptacles, using the same white neutral for both receptacles, and of course the bare ground would be linked all the way around. That way, if I plug two power tools into the same work station, they can be on two different circuits.
My question is: Is there a problem with using the same neutral on two different circuits? Or do I need use a double run of 12-2 with ground?

In all my years of working around wiring, this one never came up.

Pastor Paul
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"If they don't have woodworking in heaven, I ain't going!!!"

[Bill Kunert]

I worked for Xerox for 23 years as a tech rep. Many of our machines were run off 220 but the actual electrical system was all 110volt. The machines would draw near their rated current off each leg of the 220 line and the only return was the neutral of the same size as the hot sides. I basically wired the outlets in my shed the same way. Put in 2 20 amp gfi outlets and ran 12/3 with ground from the house. I used a common neutral. I think the legs are out of phase so even drawing 20 amps on each line wouldn't result in 40 amps on the neutral. Hope I'm right about this. Don't want a flame.
Regards
Bill

[deathwish2]

Yes Pastor, that will work . . . you do have to make sure that each of the hots is from a different 'leg' in the breaker box (like you were wiring a 220 circuit). To make sure you don't zap yourself in the future, you'd want to use a double pole (220) breaker for the two circuits in question, that way when you shut off one half of the duplex, both are shut off.

I had thoughts similar to Bill's and they were confirmed and clarified by Sonny a while back. I had gone a step further than you and put both duplex 110's and single 220's on the same 20A double pole breaker in the shop area . . . but the theory holds true even with the 220's out of the equation.

[PastorPaul]

Mark,

I had thought about using the double pole breaker, but it requires me to kill both circuits at once, even if I don't need to. I figure to put two slim-line single poles in (one above the other, which takes some special placement to make sure you don't just give yourself two circuits on the same line), and just get into the habit of turning them both off at the same time. That leaves me the option of leaving one powered up when I need to. It's either that or use the double pole slim-line (still have to straddle when using the slim-line) that allows you to pull the strap that connects the two trip switches. Gotta do some more investigating.

Pastor Paul
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"If they don't have woodworking in heaven, I ain't going!!!"

[TDHofstetter]

Wait wait wait hold up stop desist.

The only slimline double-breakers I'VE ever seen were served by only one leg in the box - they cannot supply you with power from both legs at the same time. These ARE the ones that, together, occupy one slot... right? That won't work. In order to use a single neutral, the two "hots" MUST MUST MUST be split between the two legs. Otherwise, you'll fry the neutral before you ever pop a breaker.

Ya gotta use TWO slots to get both legs.

Uh, I know how that sounds... just don't think of it that way. :)

-- Tim --

Tot homines,
Quot veritas,
Quot vias.
Suum quoque.
Sic vita.
(sp?)

[deathwish2]

>I had thought about using the double pole breaker, but it
>requires me to kill both circuits at once, even if I don't
>need to.

Keyword . . . ME . . . I'm thinking more from a safety standpoint than a convenience one. Down the line, if someone (other than you) needs to replace the duplex fixture due to failure, they may not know that there are two circuits on EACH duplex fixture . . . the double pole breaker will force them to shut off both lines to the box. Anyone who isn't experienced enough to tell there are two hots after opening the 'half hot' box, may otherwise find out the hard way }>

[deathwish2]

>The only slimline double-breakers I'VE ever seen were served
>by only one leg in the box - they cannot supply you with
>power from both legs at the same time. These ARE the ones
>that, together, occupy one slot... right? That won't work.
>In order to use a single neutral, the two "hots" MUST MUST
>MUST be split between the two legs. Otherwise, you'll fry
>the neutral before you ever pop a breaker.
>
>Ya gotta use TWO slots to get both legs.
>
>Uh, I know how that sounds... just don't think of it that
>way. :)

I wasn't going to, but who knows about the Pastor :P

Anyhow . . .the ones like you describe (at least in the GE-style I've shopped for) could be put on the same leg . . . but they can, and I'm sure are meant to be use across two poles, as they carry a 110/220v capacity on the tag.

At Lowes, I even saw a FOUR-gang slimline, it was comprised of a 110v 20a, a 220v 20a double pole in the center followed by another 110v 20a . . . perfect for adding a 20a 220v to a full box where you have a pair of full height 20's to switch out . . . makes it almost easy ;)

[PastorPaul]

Tim,

I use GE and with them it is a matter of logistics. Here's what I did for my table saw:

I removed two single-pole breakers, which would have allowed for one regular double pole breaker. I put a slim-line single pole breaker in the top half of the first slot to handle one of the two circuits that lost their breaker. Next, I installed the slim-line double pole breaker, which then spanned both poles. That left room for one more slim-line single pole breaker, which took care of the second circuit that lost it's full size breaker.

The same principle applies to using all single-pole breakers. You just have to make sure that you use the two middle breakers for the two different circuits, because they are on different poles.

Pastor Paul
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"If they don't have woodworking in heaven, I ain't going!!!"

[PastorPaul]

Mark,

I am a stickler for marking things. If I don't use the double pole breaker, you can be sure things will be so clearly marked (receptacles and breakers alike) to make sure that anyone knows that both breakers have to be thrown if you are going to monkey around in there.

My main problem with the double pole is that if I lose one circuit I lose both. Then I have to wait to use the good circuit until I have time to tear into things on the bad circuit before I can use the good one.

As I mentioned, one thing that GE has, or had, is a double pole slim-line that allows you to pull a clip to separate the pole switches when you want to kill just one circuit. This may be the best of both worlds. The two circuits will be tied together, but when I need to kill just one, I just remove the clip and kill the circuit I need to kill and leave the other live. When done with whatever, I just return the clip and am back to both circuits on a single switch. I have to dig out one of my GE double pole slim-lines and check it out before I proceed.

One thing I am struggle with is how to run the wiring. Most of the current duplex receptacles, although they are singles, are where I already want them. I can either kill the power, pull the wiring, install the larger boxes, run the new wiring and receptacles, and I am off and running. The problem there is that I will be without power for the days, or weeks, it will take to do the wiring.

The other alternative is to slightly relocate the new boxes, run my wiring and receptacles, then tie the new system into the breaker box. This option will leave my old circuits live so I have power until the rewiring is done. Then I can pull out the old wiring and boxes to be reused in the rest of the rewiring of the garage (most of the garage wiring is fairly new, just not well done). I'm not worried about the holes left in the wall, since I have to insulate and drywall anyway, and the current boxes are mounted at such varied depths that few of them will line up with the new drywall.

Pastor Paul
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"If they don't have woodworking in heaven, I ain't going!!!"

[Limey]

From the title there PP I thought you had ditched the doc's advice and started training.
Don't overdo it ...

Limester