Wiring a 3rd garage stall. Do I need to start over?

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I recently added on a 3rd garage stall which I will use the majority of it as a woodworking shop. To save some money I did the wiring myself. Here is my situation.
I wanted two 20 amp circuits alternating from outlet to outlet as you go around the shop. I ran 12/3 wire from my breaker box (new Cutler-Hammer with Type CH breakers) to the garage and alternated red and black wires to alternate circuits. I intended to install a GFCI outlet at the beginning of each circuit. The inspector pointed out that sharing one neutral between the two circuits would cause both GFCI to trip at the same time. I asked if I should re-wire and he said I could get a 2 pole GFCI breaker to protect both circuits.
My questions...
1. Can I still go with 2 GFCI outlets and deal with the inconvenience of both tripping at the same time? Is there any risk in that setup? 2. Wouldn't a 2 pole GFCI breaker be producing 40 amps or am I missing something?
Help! Thanks in advance Russ
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Shared neutrals will be a problem, usually when there is a load pulled from both circuits at the same time. If you only use one circuit at a time you might have infrequent tripping.
The only way a 2 pole breaker is giving out 40 amps is if it is a 40 amp breaker.
I suggest that you get 20 amp GFCI's my little buzz box wire feed welder, is hard on the 15 amp varity.
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Do you really want to install something half-ass that will continue to give you problems? The alternative to a two pole 20 amp GFCI circuit breaker would be to install a pigtailed GFCI receptacle at every location. That would alleviate the unbalance problem.

You're missing something.

from
is
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SQLit wrote:

Are you thinking two 20amp GFCI breakers? Don't I have the same problem with neturals?
Thanks, Russ
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No, One double pole 20 amp GFCI circuit breaker and you won't have neutral problems

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amp
welder,
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I wouldn't think so, as some hot tubs have "main" gfci protection feeding assorted 240 and 120 volt pumps, blowers, and heaters

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On Tue, 31 Jan 2006 18:22:23 -0500, "John Grabowski"

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Imbalance won't be a problem with a twopole GFCI breaker. Confusion comes from this statement:

This is true, but not the way the GFCI works. The GFCI has a special ring through which both the hot and neutral wires run. Like a circus lion jumping through a hoop. The ring senses the sum of the current running through it, and the GFCI trips if this sum is ever more than 5ma (in either direction: up or downstream). The only way to keep the sum of the currents zero is obviously to have both hot and neutral exactly the same current, but in opposite directions.
The double-pole GFCI breaker just runs both hots and the single neutral through the same single ring. In your example, you get 5amp phase A on one hot, 1amp phase B on the second hot, and negative (5amp A + 1amp B) on the neutral. Course, since phase A is exactly the negative of phase B, that's really 5ampA on one hot, -1ampA on other hot, and -4ampA on the neutral. And wonder of wonders if it doesn't sum up to zero so the breaker doesn't trip.
-Kevin
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Thanks for the explanation Kevin. I never installed a two pole GFCI breaker like the original poster intends to so I had no personal experience as to whether it would work or not. Your example makes perfect sense.
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Actually it is. The whole point of the toroidal coil is to detect when they imbalance. With a two pole GFCI, the coil's just wired differently so that they detect when the neutral current isn't the difference between the two hot currents.
If you tried to do a multi-wire branch circuit with two single pole GFCIs, the toroids (plural) aren't wired right to detect imbalance properly. So they be tripped all the time.
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Chris Lewis wrote:

Sorry, I think my point was misunderstood. I was trying to point out that a GFCI has no special circuitry to examine the neutral current and the hot current and compare them. That is, the "toroidal coil" doesn't distinguish between hot, neutral, phases, whatever. Instead, it simply detects the net sum of all current passing through the coil. As you know, a one pole GFCI has two wires going through the coil, and a two-pole GFCI has three wires going through. Or, rather, in fact they would have an extra wire each for the test button, which leaks a bit of current through in one direction, then loops it around back to the supply side without going back through the coil. But the coil could care less about neutrals, hots, phases, or whatever. Talking about "balances", "comparing", etc, can be misleading. Talking about total current seems to me a much more useful way of thinking about a GFCI (since it avoids the one-pole two-pole confusion), and is a description much closer to what the circuit actually implements.

Yup.
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We're both saying the same thing, but I think the "must balance" terminology is more understandable than "net sum".
Balance says much more directly what the device is looking for, which in these sorts of discussions is more important than implementation details.
"Balance" meaning "discrete measurement" is more a digital concept.
Obviously, there's no need to have a microcomputer in a GFCI.
People forget about analog.

"Total current" is only going to make sense to people who can think in phases (or worse, vector math, and remember the left-hand-rule ;-) Otherwise, most people are going to get confused about the "zero sum" methodology in the toroid and come out with "How can it be zero (and not trip) when you're drawing current, you moron!" ;-)
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On Mon, 06 Feb 2006 21:51:09 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

They do. Analog can work quite well for special-purpose devices.

The total current (through a properly wired and non-tripping GFCI) will be zero, although I expect a lot of people to fail to understand that.
In the same way, the total current in a 3-phase wye is zero.
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Including me. Unless I had prewarning you were speaking in net sum terms. Otherwise, obviously, the total current is what is passing through a wire.
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On Wed, 08 Feb 2006 07:36:10 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

Of course, there's more than 1 wire in there, and I did say "total".
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Well, yes. But you're wearing your electronics hat, not your electrical hat.
Unless you're used to thinking of current in terms of instantaneous _direction_, and think that the hot current is balancing (and in opposite direction) to the neutral, the total isn't going to be the electronics notion of "net current flow", it's going to be the electrical notion of how much current the circuit is delivering to the load at the far end.
Which isn't the same thing. Of course.
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On Mon, 13 Feb 2006 21:40:52 -0000, snipped-for-privacy@nortelnetworks.com (Chris Lewis) wrote:

I know the difference. A GFCI is affected by the current flowing through it, not the current flowing through the load.
BTW, it is true that I've had more electronics experience.
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I know you know. The problem is with people who don't have an electronics hat ;-)
[The "you" in the quoted sentence wasn't supposed to be _you_, Mark, but a generic "you". Oops. Sorry about that.]

Sorry to belabor it, but you did it _again_, Mark ;-)
Most electrical tradespeople (and most DIYs) would be thoroughly confused by that statement. I think an electronics person would also be. [Unless they've been following this conversation. But, everybody's probably ignoring us now ;-) You (generic you ;-) may catcall and boo now ;-)]
Let's try something a little more precise - something that expresses a electronics notion in terms understandable to "pure" electricians:
A GFCI is affected by the net sum of current flowing through the current carrying conductors, remembering that in a circuit without leakage, the net current flow will sum up to zero.
[Eg: in 120V circuit, the hot and neutral have equal and opposite direction currents. In a pure 240 circuit, the same is true of the two hots. In a 240/120V circuit, if the hots differ, the neutral makes up the difference, and it still sums up to zero.]
A GFCI is an elegantly simple circuit.

It shows ;-)
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On Tue, 31 Jan 2006 16:27:17 -0500, "RBM" <rbm2(remove

If sharing neutral before the GFCIs (line side) is causing a problem, you won't have eliminated it. The design of breaker boxes (and connections to the street) has a single neutral.

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