'nuther Electric wiring query

[Robert Bonomi]

This wiring method, the so-called "Edison circuit', *is* allowed in at least some parts of the U.S. No problem with it, anywhere in the greater metro Chicago area, for example. I recently re-wired my kitchen, in this

-precise- manner, and the city electrical inspector had no problem with it. He actually wondered 'why so *many* _neutral_ wires?' -- 'cuz I had outlets on opposite sides of the breaker panel on the _same_ breaker. The two hot leads were spliced together in a junction box just before the panel (no splices allowed _in_ the breaker box), but both neutrals ran straight through to the bar in the breaker box. Simpler than running wire to the left-side outlet, and then _back_, and over to the right-side outlet. 'Unconventional', but sound engineering, _and_ code-compliant.

As long as the two hot legs are on opposite phases of the 240V feed, the neutral carries only the _difference_ in the two loads. 'Best case' is that there is -zero- current in the neutral; 'worst case' is that there is current in the neutral that is the same as -one- of the hot legs (where the other hot is supporting -zero- load at that time)

If you use GFCI _outlets_, then there is *no* problem. Speaking from direct experience here.

To use 'downstream' outlets from a GFCI outlet, you *do* have to have a 'unique' hot, _and_ a 'unique' neutral, from the GFCI device to the downstream outlets. You cannot share _that_ wiring across GFCIs.

I'm *not* sure about GFCI _breakers_, having never actually _used_ those devices. I would _suspect_, however, that they work in the same manner -- that you can't 'share' the neutral downstream of a GFCI breaker. "Read the directions" is indicated.

[Mike Marlow]

box.

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.

[Al Reid]

Your analysis is absolutely correct.

[Doug Miller]

And I'm absolutely certain that you're wrong.

This is specifically permitted by the NEC, provided that: a) the two hot conductors are on opposite legs of a 240V service, and b) both hot conductors can be disconnected by *one* disconnect. This is easily implemented with a standard two-pole breaker.

If it is installed in compliance with the NEC (see above), the current in the neutral is the _difference_ of the currents in the two hots, not the sum.

Well, you did get that part right.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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[Swingman]

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.

[Doug Miller]

It is perfectly safe, and does not violate code, as long as: a) the two hot conductors are on opposite legs of a 240V service, *and* b) a *single* disconnecting means will disconnect *both* of them at once. Both of these criteria are easily satisfied by using a standard two-pole breaker: the two sides are necessarily on opposite legs, and one handle disconnects them both at once.

It's not necessary to mark the red wire black, as red wires are assumed to be hot anyway. The conductor color requirements in the code are pretty simple: Ground: bare, green, or green with a yellow tracer Neutral: white or gray Hot: Anything else.

little help here....

You're fine.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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[Doug Miller]

GFCIs operate by sensing the currents on the hot and neutral. If they differ by more than 20ma, the GFCI opens -- the point being that if the currents are not the same, then there must be leakage somewhere.

Consider this:

red -----------------******** * * white -----------------* GFCI *------------*************** (neutral) * * * insert 120V * ******** * load of your* * choice here * black -------------------------------------***************

As soon as a load of more than 20ma is applied between the black and the white, the GFCI will trip, because the current in the white wire does not balance the current in the red wire.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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[Doug Miller]

In a *properly* wired circuit of this type, the neutral carries the

*difference* of the individual hot currents.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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[Doug Miller]

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.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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[Doug Miller]

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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[Doug Miller]

Yes.

I'm sure you meant 12/2 here.

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[Doug Miller]

Geez. Here we go again.

Yes, it is allowed by the NEC, as long as the two hot conductors are on opposite legs of the 240V service, and a single disconnect, disconnects them both. This is easily implemented by using a single double-pole breaker. With the two hots on opposite legs, the current in the neutral is the *difference* of the currents in the individual hot conductors, *not* the sum, and thus can never exceed 20 amps. There just isn't a problem with doing this.

-- Regards, Doug Miller (alphageek-at-milmac-dot-com)

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[Swingman]

To get a precise answer, it is important that you clarify this. Do you want to be able to plug in two, or four, plugs in the box?

[Bob]

You are correct. My statement only applies if both branches come off the same leg.

Bob

[Bob]

Yes, I stand corrected.

Bob

[Bob]

Doug, you seem to know what you are talking about. What's your experience with how often this is actually done? It seems to me that, though legal and safe, someone might forget how this is setup and rearrange breakers/wiring in the future, creating an unsafe situation. Are there any requirements for tagging such a configuration?

Bob

[U-CDK_CHARLES\Charles]

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.

[Swingman]

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.

[_firstname_]

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 >Shared neutral is certainly legal in the U.S. For those pontificating

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.

[Robert Bonomi]

"Yeahbut" applies. For U.S.A. installations, it _ain't_ wired that way. In the case of GFCI outlets, the wiring is:

red -----------------******** (1) * * white ------------+----* GFCI * (neutral) | * * | ******** | +------------------------*************** * insert 120V * * load of your* * choice here * black -------------------------------------***************

(1) is either a 'wrap around' the screw on the GFCI, or a *continuous* strand from the breaker box, towards the 'load of your choice' with a 'pigtailed' section going to the GFCI. Has to be built such that you _cannot_ disconnect the neutral going to 'a different location'.

If the current level on red and white, _at_the_GFCI_ isn't the same, then something that is coming 'in' on the 'red' lead is going 'out' somewhere other than the 'white' lead. And the GFCI triggers.

This is _independent_ of what is happening with the '120V load of your choice'.

What I have in my kitchen is =precisely= the above, where the 'load of your choice' is _another_ GFCI outlet. I run _grossly_ 'unbalanced' loads across the two circuits all the time -- like 1800 watt draw on one circuit and *zero* on the other. Neither of the GFCIs trip.

This wiring was done per a city electrical permit, under the supervision of a licensed electrician with going on *60* years experience, _and_ blessed by the city electrical inspector.