how many ground wires for 2 circuits in conduit?

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  #1  
Old 08-18-04, 07:06 AM
mattgg
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how many ground wires for 2 circuits in conduit?

I'm running two new 20 amp circuits from the subpanel in my garage. I'm planning to put four #12 THWN conductors (two hot and two netural) in 3/4" EMT. Do I need two #12 grounds or can the circuits share a ground wire? Does it matter if the ground is bare or insulated?
 
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Old 08-18-04, 07:16 AM
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My understanding is that you can use a single ground wire.

Please make sure that you keep track of which neutral goes with which hot wire.
 
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Old 08-18-04, 07:35 AM
mattgg
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Originally Posted by racraft
Please make sure that you keep track of which neutral goes with which hot wire.
I've already thought of that. I'm going to mark one pair of conductors (one black and one white) on both ends so I can keep the pairs straight.
 
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Old 08-18-04, 11:01 AM
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You are not allowed to run 2 circuits to an out building. You can only run one circuit. It can be a multiwire circuit however. For a multiwire circuit use only one neutral and a double pole breaker properly installed to give 240 between the hots.
 
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Old 08-18-04, 11:26 AM
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Joe's comment does not apply here. He missed the fact that you said "from the subpanel in my garage".
 
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Old 08-18-04, 11:35 AM
Homer Simpson
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1. The conduit fill for 1/2 EMT would be ok. 5 conductors. This is from memory so check.

2. I you decide to run one neutral instead of two you would have to use
a double pole breaker with a tie. Also if Gfics are needed on the circuit, it would cause a problem.

3. Where did we get an out building? I thought this is in the garage.

4. Use pulling lubricant. An since emt and related boxes are metal be sure and
bond to the grounding conductor. Also, ground the recepticals.

5. bare grounding conductor is ok. But if there are long runs, turns, etc use stranded THHN wire for the conductors. Green for ground.

Say goodbye, Homer. Goodbye
 
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Old 08-18-04, 01:42 PM
rlrct
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Originally Posted by Homer Simpson

2. If you decide to run one neutral instead of two you would have to use
a double pole breaker with a tie. Also if Gfics are needed on the circuit, it would cause a problem.
Actually, the NEC only requires that "a means shall be provided to disconnect simultaneously all ungrounded conductors" if you have a multiwire circuit feeding multiple devices on the same yoke. IOW, if you were to split-wire a receptacle - you need a 2-pole common-trip breaker or breaker with handle-ties.

Ironically, it is allowed to have a duplex/triplex box, with 2/3 receptacles where each receptacle is fed by a different hot leg on a multi-wire circuit, with 2/3 independent breakers. You could kill 1 breaker, pull the cover plate and the receptacle next to the one you're pulling is hot. That's not how I'd wire it because I want to know that any circuit in the box is dead when I'm working in there, but the NEC does allow it. Go figure. NEC reference is 210.4(B) if you want to see this in ink.

------------------------------------

On the GFCI's, you can run a multiwire with single/shared neutral as far as the first GFCI receptacle. Then you need to split the neutrals.
 
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Old 08-18-04, 01:55 PM
mattgg
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Thanks for all the info, but I'm not planning to used a shared neutral. I'm also not using GFCI devices because the circuits I'm adding are for dedicated single receptacles for sump pumps.
 
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Old 08-18-04, 06:23 PM
Homer Simpson
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The facts are...

rlrct,

Respectfully, It makes no difference as he is going to use two neutrals.
But...

Out of the code book: 210-4 B

" The simultaneous opening of both 'hot' conductors at the panelboard will
effectively protect personel from the inadvertant contact with an energized
conductor or device terminal. The simutaneous disconnection can be secured
by a 2 pole circuit breaker or by two single-pole circuit breakers with a handle
tie."

The reasoning is that a duffus is going to use a double breaker on the same
buss thereby doubling the current on the neutral conductor- up to 40 amps
on a 20 amp wire. But I know, you know this. Say goodbye, Homer. Goodbye
 
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Old 08-18-04, 07:16 PM
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Smile

Homer,
With all due respect to you as well, 210-4(B) is specifically referring to a mulit-wire circuit terminating on the same yoke.

While a two pole breker is a good idea it is not code for the purposes of this discussion.
 
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Old 08-18-04, 07:18 PM
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Talking

Also, as we all know, it is against code for dufuses to be doing electrical work in the first place.
Then again, we know not everyone follows the code.
 
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Old 08-18-04, 07:35 PM
rlrct
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Homer,

Your quote of 210.4(B) makes me think you have a copy of the handbook, not the actual code. That's not a problem, but it helps to have the actual code in addtion to the interpretation of it.

210.4(B) has nothing to do with neutrals. It specifically talks about having multiple hot legs supplying multiple devices on a single yoke. A split-wired receptacle is a typical example. Another would be one of the single outlet, single toggle switch combos, where 1 circuit feeds the outlet and another circuit feeds power to the switch. Notice no mention of neutrals here. The point of the NEC is that, to work on the device, all hot legs must be simultaneously disconnected.

In terms of doubling the return current flowing through a shared, multiwire neutral - someone would need to work pretty hard to achieve that. The easiest way to make the mistake is to use a pair of half-size breakers next to each other. Any other combination of side-by-side breakers will result in poewr being drawn from both busses and the shared neutral will be the difference in current between the 2. If you want to separate the breakers in the panel, then you could pretty easily double that return current.

So, the reasoning of 210.4 has nothing to do with the return current. It's all about the hot legs feeding the devices on 1 yoke.
 
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Old 08-19-04, 12:03 AM
Homer Simpson
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Addendum

Speedy Petey and rlcrt,

It was my impression that the garage was being wired for recepticals.
whether you could have 1 grounding conductor or was required to have
2 grounding conductors has been addressed.

I didn't know that this was for 2 sump pumps. Mea Culpa

Yes, this did come out of the handbook, but every section of the code is in the handbook with the added benefit of theory and rational.
Many a time the rational in the handbook has corrected a building inspector's
faulty interpetation of a code section. I have used them since trade tech and I continue to use them with an occassional suppliment for that reason.

As for disconnecting the energized conductors, it must be done. However, the rational of using a 2 pole breaker or 2 full space breakers addresses the issue of overloading the neutral conductor not the disconnecting means. You
can disconnect the energized conductors with a double or twin breaker, but it
is on the same buss with the potential for overload. As far as, rarely happening, with today current hungry devices it can happen easily. A hair
dryer draws 1500 watts, for pete sake. If the neutral conductor is carrying
30 amps what's going to shut down the circuit. Melt down is. The rational
addesses the neutral;the code section addresses the disconnecting necessity.

I have run accross my share of licensed contractor making misakes, some
pretty grievious. My pencil has an eraser on it, too. But I come accross duffuses that shouldn't be allowed with in ten miles of an extention cord.
An some guy who doesn't know one breaker from another or it's application
will substitute a double for a 2 pole because it is cheaper.

Say goodbye, Homer. Goodbye
 
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