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#96097 - 11/02/05 07:46 PM New panel/gutter question
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Say someone retrofitted a new panel and installed a gutter above the panel to splice the short cables.
Assume they feed all the spliced circuits into the panel via a single big nipple.
Can they just put an isolated neutral bus bar and a ground bar in the gutter feeding back to the panel with two appropriatly sized conductors?
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#96098 - 11/02/05 10:31 PM Re: New panel/gutter question
mhulbert Offline
Member

Registered: 10/19/04
Posts: 133
Loc: Anaheim, CA USA
Yes.

I do it all the time with EGC's, however, I'm not sure about doing it on the neutral...if you lose that large jumper, you may fry some of your loads. Maybe it would be better to parallel 2 or 3 conductors for redundancy?

If you look at "column width" panelboards, they do this as well, with a large j-box at the top with a wireway going down to the panelboard.

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#96099 - 11/03/05 03:49 AM Re: New panel/gutter question
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
The inspector might be interested in how full the nipples are and what the neutral load is and what size the wires are that you are putting in parallel.
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#96100 - 11/03/05 08:24 AM Re: New panel/gutter question
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
Actually "fill" was one of the reasons I though this would be done.
If you took the example of 20 120v 20a circuits, you would have 20 blacks, one 2ga neutral and one 4ga EGC. (~.55 sq/in) That fits in a 1.25" @ 36.33%. You can load a short nipple more than that and a 2" nipple would give you lots of breathing room.
Any 240v circuits without a neutral load could come down in another nipple.

I agree you can't parallel anything smaller than 1/0 but if you wanted "belt and suspenders" for the open neutral concern, you could parallel a 1/0 neutral, adding an extra .14" to the fill.
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#96101 - 11/03/05 09:43 AM Re: New panel/gutter question
winnie Offline
Member

Registered: 09/15/03
Posts: 652
Loc: boston, ma
Code has explicit permission for multiple sets of feeders sharing a single suitably sized neutral, and has explicit permission of multiple ungrounded conductors _with voltage between them_ sharing a single neutral (multi-wire branch circuit), but I don't recall anything that either permits or prohibits multiple circuits sharing a single suitably sized neutral.

I would be rather uncomfortable, for example, with 2 #12 conductors on the same supply leg fed through 2 20A breakers, both sharing the same #8 neutral. The installation being discussed here is essentially an extension of this sort of concept.

However the strongest reason that I can come up with for not sharing the neutral in this nipple is that it would not work with any sort of breaker that needs to sample the neutral current, in particular GFCI and AFCI breakers.

On the parallel conductors, while you are not permitted to parallel conductors smaller than 1/0, I be comfortable with smaller conductors paralleled for redundancy, with 2 provisos: the conductors are all in the same conduit or raceway, or are in non-metallic conduit, and that each individual conductor be suitably sized to carry the entire load. Basically, if no hazard would be created if the parallel connection would fail, then I would be comfortable with more relaxed requirements for parallel conductors.

-Jon

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#96102 - 11/03/05 05:26 PM Re: New panel/gutter question
HotLine1 Offline

Member

Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
My 2 cents:
As winnie said, GFI/AFCI excluded, I see no problems with what you proposed, and your spec.

Now, as to sizing the ground.....would you not base the ground conductor on the size of the OCP, or the largest OCP for the branch circuits involved??

(That's an opinion someone laid on me, I tend to agree with Greg's specs)

John
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#96103 - 11/03/05 06:11 PM Re: New panel/gutter question
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
See 300.3(4)
http://www.markhellerelectric.com/300.3(4).pdf

You can do it... But something tells me, at least, at one point or another the auxilliary gutter was to be listed for the purpose, but if you are allowed to do it in any junction box, I might start doing it myself more often, just to get rid of some fill in some of the tighter panels.
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Mark Heller
"Well - I oughta....." -Jackie Gleason

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#96104 - 11/05/05 02:40 AM Re: New panel/gutter question
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I challenge anyone to point to a code section that prohibits using one properly sized grounded conductor for multiple circuits as Greg described or for any branch circuit wiring.

The 2002 NECH even shows how it is done.


Exhibit 225.3 A 120/240-volt, single-phase, 3-wire system (branch circuits rated at 20 amperes; maximum unbalanced current of 80 amperes).



FWIW I do not understand the worry expressed in loosing the neutral, if we worry about that than how would we install feeders or services?

Bob
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Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#96105 - 11/06/05 06:57 AM Re: New panel/gutter question
George Little Offline
Member

Registered: 01/18/04
Posts: 1492
Loc: Michigan USA
Bob- you've selected a very unique example for your point and I have never seen this type of installation installed. It is only usable outside as 225.7 states. All other type of installation would have us sizing the neutral to match the individual branch circuit.
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George Little

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#96106 - 11/06/05 07:04 AM Re: New panel/gutter question
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
George please cite a code section that prohibits doing this in any branch circuit.

I have been down this road before so you have an up hill battle.

Bob
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Bob Badger
Construction & Maintenance Electrician
Massachusetts

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