'nuther Electric wiring query

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"Mike Marlow" wrote in message

Granted he is using layman's terminology, but are you sure that's what he meant? ... cuz it damn sure ain't what he said:

A single is one outlet, a "pair", or duplex, is two outlets in the same box.
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I think you're reading into what he wrote. Maybe it's just the way I see it, but I interpreted what he wrote to mean two of something. Not as in a standard duplex, but as in two separate devices - whether they are single outlet or duplex.
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I will agree that you can take it either way, Mike.
However, it makes no difference... what I said in my original post will still work as a "split circuit" whether the box is a duplex, fourplex, separate boxes four feet apart, or even a single outlet at the end of the run.
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Hello there -
Well, a wealth of posts to the point of confusion as to who's saying what... anyway, I *am* a layman, and apparently don't have the nomenclature korrect, I want a total of 4 plug-thingies in a double box, thus two pair... the left on 1 circuit and the right on the 2nd circuit... But, for now, I have decided to just run 12/2 and say the hell with it...
John Moorhead

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"John Moorhead" wrote in message

LOL ... I stand corrected.
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Not if he's using two duplex receptacles in each box, as it appears he intends. And even if he's using one duplex receptacle per box, with each half on a different phase, he still needs to remove the bridge *only* on the hot side.

Ummm.... no. That would be *one* two-pole circuit breaker.

Not necessarily. That's one duplex receptacle, with each half on a different leg. It sounded to me like he intended each box to have two duplex receptacles, with each duplex on a different leg.
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"Doug Miller" wrote in message

If you had looked, you would have seen that an immediate post clearly indicated I had inadvertently left out the word "hot".

I seem to be in the minority, but I am still not certain as to whether that is exactly what he meant?
Nonetheless, around here it is still referred to as a "split circuit" whether it be in a duplex or fourplex box, or a series of same.
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It is simply a multiwire circuit. As long as you use a 240v breaker for the two circuits, it fine; maybe.
If you need a GFCI, such as in a garage or a finished basement, you will have problems. They have 240v GFCIs, but I have never used one and don't know if they work on multiwire circuits or not.
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I disagree. You are allowing 40 amps (2 * 20) across a single conductor (the neutral) by sharing it with two single phase 20 amp circuits.
Bob
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On Fri, 03 Dec 2004 18:53:58 +0000, Bob wrote:

I disagree. As long as each breaker is on the opposite hot as in any 240V circuit, the total neutral load will never exceed the current draw of the largest circuit load. If each circuit was drawing an equal load, the neutral load would be zero.
-Doug
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Your analysis is absolutely correct.
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You are correct. My statement only applies if both branches come off the same leg.
Bob
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Which is, of course, exactly the reason that code prohibits doing that way.
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Nope, not if the two hot conductors are on opposite legs of the 240V service (which is the only way to meet code). In that case, the current in the neutral is the *difference* of the two hot currents, not the sum.
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On Fri, 03 Dec 2004 16:56:53 GMT, "John Moorhead"

So far the answers you've gotten are either wrong or way wrong.
Shared neutral is certainly legal in the U.S. For those pontificating on how it's allegedly unsafe, the two hots MUST be fed from a duplex breaker, which does two things: it ensures that both feeds are on opposite buses which means that the neutral currents for each branch are 180 out of phase and thus subtractive, and it ensures that when the breaker is tripped (intentionally or otherwise) there are no hot leads in a box with two separate branches in it.
So the short answer is, yes, you can do that.
The long answer is I don't like shared neutral circuits and avoid them like the plague. Call it personal prejudice but you have to make sure you have a continuous neutral (all pigtails to the receptacles) so that you don't wind up with 240V across the devices if the neutral is lost.
Wire is relatively cheap. No matter how big your shop (well, up to a reasonable size, anyway), you'd be hard pressed to add $100 to the bill by wiring two completely separate circuits. Of course if you do it that way I wouldn't recommend putting receptacles fed by two different circuits in the same box. Same issue as with the shared neutral circuit if a duplex breaker weren't used.
- - LRod
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I didn't assert "Unsafe" but rather "I'd heard it was Canadian practice but never heard of it being done in the States."
I've certainly never seen it here in NJ.
OTOH, a duplex breaker will certainly be safe, so there you (or he) goes.
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Agree. Even after this excellent post, a whole stream of wrong answers kept coming. Fortunately, there were also a few right answers.
Rule #1: DO NOT TRUST SOME RANDOM POSTER ON USENET. For all you know, we might be all homicidal maniacs. Furthermore, not all localities use just the NEC, some have additional electric codes. Call either the building inspector in your locality, or talk to a real (experienced and licensed) electrician in your area.
That having been said ...

Completely agree. More discussion of GFCI below, though.

Partially agree, partially disagree. Agree: If you use them to feed the two halves of a duplex receptacle, I think they are dangerous. Because (a) there are 240V across components that are physically very close together, and (b) all you need is one wire to come loose, and you have 240V across the load.
On the other hand, if you use them to feed separate receptacles, I think they are acceptable - they end up being a way to save wire and time (it is easier to string one 12-3 than to string two 12-2 next to each other). Just use extra care in wiring the neutrals (*) together, to make sure they don't come undone.
Even better: They make raceways with built-in outlets (wiremold is a popular brand). This stuff looks like a metal tray, about 1" square, and it has an outlet ever few inches or every foot. This is ideal for feeding power at counter height in a shop. And you can get it pre-wired for two circuits: One neutral conductor, one ground conductor, and two hot conductors. This makes a perfect match to an edison- or multiwire circuit with a dual-pole 20A breaker: With very little work, you have two 20A circuits everywhere in your shop, and you'll never run out of outlets. This type of multioutlet assembly (technical term for the wiremold stuff) has to be fed from an edison- or multiwire circuit. This is what I have installed in my basement shop.
The only real problem is how to add GFCIs. One option is to use two (or more) individual GFCI outlets at the endpoint of the edison circuit. The problem is: if you want to add the "load" connection of the GFCI outlet, you must never merge the neutrals back together. So behind the GFCI, the circuit is no longer an edison- or multiwire-circuit. If you want to use multi-outlet assemblies (like the wiremold stuff), or a split duplex receptacle (one outlet on each of the circuits), there is no simple way to add GFCIs. You can't just put two GFCIs next to each other, and feed through them, because merging the two neutrals back together is a no-no (not just illegal, it will just plain not work). In this case, you have to use stronger medicine: A 2-pole 240V GFCI 20A breaker in the panel. Those exist, but they are very rarely used, and therefore pretty hard to find (the borg doesn't stock them). The real bad news is the cost: I paid a little over $100 for the GFCI breaker. So if you need GFCI protection (basement, garage, outdoors, etc.), this negates any potential cost saving.
(*) The term "neutral" is not used in the code for 240V circuits, or edison- or multi-wire circuits. Instead, it is called the "grounded conductor" (a.k.a. the white wire). Don't confuse that with the "grounding conductor" (a.k.a. the green wire). The colloquial term "neutral" is much clearer, and in common use. Unfortunately, to further confuse the issue, the code uses the term "neutral" for certain cases of three-phase circuits.
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No.
The neutral is a current carrying wire in a single phase circuit. You should run 12/3 for each circuit. I think you may be trying to be too symmetrical and neat by putting two branch circuits in the same box. It also crowds the box and makes connections more difficult. But I'm assuming that you are placing outlets at some reasonable spacing for a shop (Lots of 'em).
Its only an opinion, but my philosophy is to use multiple outlets for connectivity, as opposed to load carrying capability. My shop has three heavily interactive walls (bench and portable tool areas). I put one branch ciruit in each area and populated it with an embarrassingly high number of outlets. I also ran one 220 ciruit to each area with 3 outlets each.
Bob
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Yes.
I'm sure you meant 12/2 here.
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Yes, I stand corrected.
Bob
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