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#26467 - 06/12/03 07:13 PM One neutral or 2
spkjpr Offline
Member

Registered: 12/01/00
Posts: 226
Loc: Sedalia,MO, USA
Hooking up a line in a manufacturing plant that has 1 120VAC ckt for recpt. and 1 120VAC for motor controls, using foot pedals. The other electrician on the shift and myself ran 2 neutrals, the day shift guy said he would use one for both. Just wondering what most of the rest of the guys here would have done? Thanks.

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#26468 - 06/12/03 07:22 PM Re: One neutral or 2
Electric Eagle Offline
Member

Registered: 04/20/02
Posts: 928
Loc: Alpharetta, GA
I would've use one for both, but if you do you must use a pole breaker with a common trip handle. This insures that each will be on a diferent phase and that the neutral can't have power if either circuit is being serviced.

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#26469 - 06/12/03 07:33 PM Re: One neutral or 2
CanadianSparky Offline
Member

Registered: 03/05/01
Posts: 86
Loc: Alberta Canada
Depends how hard it was to get the other neutral there. But even if it wasnt easy I'd probably still run the separate neutral. Easier to isolate individually.

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#26470 - 06/12/03 07:36 PM Re: One neutral or 2
spkjpr Offline
Member

Registered: 12/01/00
Posts: 226
Loc: Sedalia,MO, USA
The first thing I thought of was the breaker requirement. I'm sure that it is going to be wired on 2 SP breakers, as there are no DP breakers in the panel.

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#26471 - 06/12/03 08:21 PM Re: One neutral or 2
caselec Offline
Member

Registered: 04/14/02
Posts: 557
Loc: San Jose, CA
Why would this multi-wire circuit need to be connected to a multi-pole common trip breaker? The NEC does not require multi-pole common trip breakers for multi-wire circuits and using one is not a good idea in my opinion. Why should you loose both circuits if one of the circuits trips?

Curt
_________________________
Curt Swartz

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#26472 - 06/12/03 08:54 PM Re: One neutral or 2
Electric Eagle Offline
Member

Registered: 04/20/02
Posts: 928
Loc: Alpharetta, GA
Curt, I don't have the book with me but the NEC absolutely does require a common trip breaker for multi wire circuits. This is a double safety feature. If you don't use a common trip breaker and both circuit get put on the same phase, the nuetral may carry up to twice it's intended load(1 circuit pulls 15 amps another pulls 18 amps, then the neutral is carrying 33 amps) - Not Good!

Also both circuits must open at the same time to prevent stray voltage on the neutral when working on either circuit.

If someone doesn't beat me to it I'll cite the code in the morning when I get to the office

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#26473 - 06/12/03 09:01 PM Re: One neutral or 2
DaveB.inVa Offline
Junior Member

Registered: 02/25/02
Posts: 6
Loc: Nickelsville Va
210.4(C)

Line to neutral loads. Multiwire branch circuits shall supply only line to neutral loads.

Exception 2.
Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch circuit overcurrent device.

This exception only requires a common trip IF you are serving a line to line load using a multiwire branch circuit.

210.4(B)
Only requires a common trip when the multiwire branch circuit is supplying more than one device on the same yoke. Even then this is only for a dwelling. Anything else doesnt require a common trip.

The above scenario isnt in a dwelling so 210.4(B) is out, and no line to line loads are served so the requirement for a common trip is out as well.

[This message has been edited by DaveB.inVa (edited 06-13-2003).]

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#26474 - 06/12/03 09:02 PM Re: One neutral or 2
Anonymous
Unregistered


Eagle,
With all due respect I don't think you will ever find that in the NEC.The only requirement, to my knowledge, is that a two pole breaker or handle ties be used if both circuits land on the same yoke.
Brian

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#26475 - 06/13/03 02:28 AM Re: One neutral or 2
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
2002 NEC 210.4(B) does not require a common trip breaker, this was pointed out to me on this forum in another post.

You can use a common trip breaker or you can use a approved handle ties with single pole breakers.

2002 NEC
 Quote:

210.4 Multiwire Branch Circuits.

(B) Dwelling Units.

In dwelling units, a multiwire branch circuit supplying more than one device or equipment on the same yoke shall be provided with a means to disconnect simultaneously all ungrounded conductors at the panelboard where the branch circuit originated.


2002 NEC Handbook commentary on this.
 Quote:
The simultaneous disconnection can be achieved by a 2-pole circuit breaker or by two single-pole circuit breakers with an approved handle tie,


[This message has been edited by iwire (edited 06-13-2003).]
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#26476 - 06/13/03 04:43 AM Re: One neutral or 2
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Just a practical reson that it may be undesirable to use a multi-pole breaker on a multi-wire circuit...
In commercial or industrial lighting, a fault on one circuit would kill all 3 or both lighting circuits. This could possibly leave a whole plant, or office wing in the dark.
Economically speaking, if you were to run a neutral (or grounded conductor ) for each circuit, you would lose all lighting bids due to excessive material costs.

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