'nuther Electric wiring query

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Folks -
I'm back... Now it's a wiring question. I'd like to run a string of outlets at benchtop height, and run two circuits. I'll put a pair of outlets in each box, 1 on each circuit. Can I safely run 12/3 for a pair of 20 amp circuits using a common neutral (white) and ground? I'd run the red wire (marked black) to one outlet and the black to the other. The two outlets would share the white wire, along with the grounds.
At the panel, I'd have the red (marked black) wire going to one CB and the black one to a separate CB. If I can do this, I'd have to string way less NM... Would this be a violation of code? Is this safe?
I know, I know... call an electrician or an EE... I'm just trying to get a little help here....
Thanks in advance!
John Moorhead
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On Fri, 03 Dec 2004 16:56:53 GMT, John Moorhead

Are you Canadian? Something similar to that--perhaps exactly--is standard for kitchens in Canada. I think they may require seperate jackets, but perhaps not.
I don't think it meets code in the US. At the very least, I've never seen it recommended for US practice.
Why not just alternate curcuits?
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Nope - I'm in Northern California... Well, I *do* want alternate circuits... The reason for using a single run of 12/3 is that I wouldn't have to run an additional separate length of wire - everything would be in the one cable. Sorry if my post didn't make that clear...
John

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On Fri, 03 Dec 2004 17:35:51 GMT, John Moorhead

I'm reasonably certain that's not allowed in the US.
In any case, the lone neutral lacks the capacity for both circuits. Also if it's in a garage, the GFCI will sense the imbalanced current and trip.
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wrote:

wouldn't
in
Seems to me that shared neutrals are allowed under some circumstances, but I can't recall if you have to downgrade the cirucuit when doing so. Wait for some of the electricians to weigh in on this one.

I don't see how this would happen. The potential between neutral and ground are the same as if you had run a separate neutral.
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A GFCI works by detecting a difference in the amount of current flowing though the hot conductor and the neutral. I think this is what he is referring to. The neutral will carry the sum of the two branch circuits.
Frank
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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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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.
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"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.
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snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) wrote:

Not by someone who understands what he's doing, anyway, but it certainly *can* be wired that way. Doesn't mean it's right, of course... and anyone who doesn't understand how GFCIs work, and how current flows in an Edison circuit, is going to be left scratching his head wondering why the GFCI on leg 'A' trips as soon as he flips on a light switch on leg 'B'.
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Gotta add "incapable of reading _and_following_ the directions" to the skill- set. <grin>
All the instructions I've seen were _quite_ explicit about using the 'load' side terminals on a GFCI outlet only for wiring to a downstream isolated outlet. That you had to run _both_ wires from the 'load' side of the GFCI to the other outlets. In fact, as they come out of the box, both the load side fittings are taped over (single piece of tape), so you -can't- 'accidentally connect something up to them.
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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. <grin>

Bzzzzt!
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. <grin>
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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.
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What you want to do is legal and safe only so long as each of the two circuits are a different phase (i.e. a different leg of the 220v). It is also considered wise to handle-tie both breakers (or use a 220v breaker) so that you cannot have a situation where one conductor is live and the other isnt.
If the current carrying conductors are on different phases the current in the grounded conductor approaches zero. If they are on the same phase, the current in the grounded conductor will be the sum of the current in each of the current carrying conductors. This would be considered bad (e.g. 40 Amperes through a AWG 12 conductor).
scott
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Wire's cheap. Don't skimp.
Patriarch
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Patriarch -
I agree, the issue isn't cost... It's time and effort... If I could run a single 12/3 and get two circuits, it would save another run... But after reading all of these posts, I've taken the 12/3 back and will play it safer and have two complete separate runs for 20a circuits using 12/2 and GFCI's with other outlets connected "downstream"
Believe me... I haven't skimped on ANYTHING with this project - ask my wallet!
John
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<snip>

That's been pretty obvious from the pictures and the enthusiasm.
I think I've spent almost as much on the electrical work as I did on the Unisaw. I don't worry that it wasn't done right, however.
There are more than enough things that go bump in the night...
Patriarch
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"John Moorhead" wrote in message

outlets
a
What you are looking at is a "split circuit" receptacle. It's been perfectly legal in a number of locale's, but I am not sure what the latest NEC says about it.
Two caveats that are generally required to do it:
1. You must cut or remove the metal bridge on the duplex receptacles
2. It is generally required that you must use two, two pole circuit brkr's, with the two circuit brkr's "tied" together so that if one trips, they both trip.
In any event, the terminology you want to use with your building inspection department is "split circuit receptacle".
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"Swingman" wrote in message

Sorry, I left out the word "hot": That should read "cut or remove the metal bridge on the HOT side".
The neutral wire metal bridge in the receptable remains intact.
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wire
outlets
the
less
get
perfectly
brkr's,
both
inspection
Look at it again Swingman - he doesn't want to split an outlet, he wants two duplexes together in a double box that have their own hots, but share a neutral and a ground.
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