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#93918 - 06/23/05 02:03 PM Branch circuits from different panelboards in same conduit
Radar Offline
Member

Registered: 04/30/04
Posts: 344
Loc: Los Angeles, CA
Here's a situation maybe you all can help me with. On one particular design / build project, the electrical subcontractor is proposing to place branch circuit wiring from two different panelboards in the same conduit run. The idea here is to feed a string of light fixtures from alternate panelboard circuits and save a little on conduit in the process.

The first light would connected to a circuit from panel A, the second light on panel B, the third on A, and so on alternating back & forth. The string of lights is between the two panelboards, so the branch circuit conduit would run from panel to panel with a J-box at each light fixture location. The light fixtures themselves are surface wall mount fluorescents mounted just below the J-box, and have a short piece of conduit to connect to the afore mentioned J-box.

Back when I was a field foreman, we never dreamed of doing something like this. The reasons seem so obvious, but I am unable to find anything specific in the NEC that precludes it. In fact, NEC 300-3(c)(1) would appear to support their proposed design.

Thanks for any clarification,
Radar
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#93919 - 06/23/05 02:13 PM Re: Branch circuits from different panelboards in same conduit
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
Radar I am not sure what you mean by

 Quote:
The reasons seem so obvious,


but code wise this installation is fine.

It is just a design issue.

Of course that is assuming other code articles are followed like derating etc.


Bob
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Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#93920 - 06/23/05 05:15 PM Re: Branch circuits from different panelboards in same conduit
e57 Offline
Member

Registered: 05/27/03
Posts: 2837
Loc: S.F.,CA USA
The only reason I wouldn't do something like that is if the came from different meters. I don't like having metering mixed, even if they are for the same customer. And seeing that they are from panels from different locations, I would probhably use striped wire for one. Just to make sure they don't get connected by the neutral by accident, although that would only be required if they were from different transformers, but still a wise idea.

Don't really understand why, the guy is doing it. Does this serve some purpose? Like say one was from a UPS, or generator.
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#93921 - 06/23/05 05:57 PM Re: Branch circuits from different panelboards in same conduit
Gregtaylor Offline
Member

Registered: 03/02/05
Posts: 212
Loc: Boise, Idaho, USA
Yeah, my question is also,why? It's legal. After all, circuits of different voltage can be in the same conduit so it stands to reason that two sources is OK. It's just a strange design.

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#93922 - 06/23/05 07:38 PM Re: Branch circuits from different panelboards in same conduit
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5035
Loc: Blue Collar Country
One code issue that comes to mind is the requirement that neutrals from different systems be identified; you are required to have all the conductors of a circuit come from the same source. Mixing them up in the same pipe can lead to all sorts of interesting problems.

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#93923 - 06/24/05 01:35 AM Re: Branch circuits from different panelboards in same conduit
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
reno keep in mind different panels are not necessarily different systems.

Check out e57s post. ;}
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#93924 - 06/24/05 06:55 AM Re: Branch circuits from different panelboards in same conduit
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5035
Loc: Blue Collar Country
IWire- nice smile! I don't want to get bogged down in what is a 'different system.' It just doesn't seem like a good thing if the "hot" wire comes from one panel, and the neutral goes to another- even if the two are simply separate load centers from the same service!

I believe the code says all conductors for a circuit must be in the same raceway....I would think that meant the neutral has to go back to the panel the hot comes from. If you don't identify the neutrals, it is all too easy to get them mixed up....and that's where the trouble starts.

So how do you identify a nuetral? My personal favourite way is to run a colored "Sharpie" along the wire, leaving a SINGLE stripe. That way, I know the red stripe goes with the red wire, etc.

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#93925 - 06/24/05 07:06 AM Re: Branch circuits from different panelboards in same conduit
Radar Offline
Member

Registered: 04/30/04
Posts: 344
Loc: Los Angeles, CA
Thanks for all your input. To answer Bob's first question, and as addressed in other posts, this concept seems repulsive to me from a workmanship point of view, the possibility for errors by installers and/or future workers is just too great and very dificult to troubleshoot. I and another foreman once spend a few days in a new highrise in LA tracking down and correcting a half dozen or so crossed neutrals in exit lights (emer & norm). I can't tell you how much fun that was!

Without being specific concerning location, the two panels in this case are far enough apart that they are most probably on different meters, although the same customer and same utility. I'm thinking they're about a mile apart. Voltages are the same, but different utility meters.

The reason for the alternating panel circuits in the first place is that's what is indicated in our preliminary (as-bid) design. We do this so that in the event that an entire auxiliary power station bites the big one, we don't loose all the lighting. Every other light is still powered from the neighboring power station. Again, I am avoiding specific locations here.

I believe the main reason for considering the single conduit is to economize; minimize costs on a firm fixed price design / build contract. After all, a single conduit is less expensive to provide and install than two are, even if it is a size bigger.

Thanks again for the great responses,
Radar
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#93926 - 06/24/05 01:48 PM Re: Branch circuits from different panelboards in same conduit
energy7 Offline
Member

Registered: 06/10/02
Posts: 58
Loc: Oxnard, CA, USA
Radar,
Oh! Wait!!! The "separate meter" part is BIG. That gets back to the reason for 230-2, especially (e)Signage.
Think of the Fire Dept Responder who thinks he just de-energized a power to the room before they pump 125 GPM of fire water all over, only to find half the circuits in the pipe still energized.
Got to have separate conduits, signage/labeling, "billboards, red flags, pom-poms".
Sorry, I got carried away!

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#93927 - 06/24/05 02:09 PM Re: Branch circuits from different panelboards in same conduit
Radar Offline
Member

Registered: 04/30/04
Posts: 344
Loc: Los Angeles, CA
Well, we would fall under the 'By Special Permission' claus in exception #4 of 230-2(a). Besides, I'm only reasonably, not entirely, certain the panels will be metered separately.

However, this illustrates my concern. I think the fire responder issue would apply to anyone who may have to work on the system in the future. Imagine getting into a J-box thinking you've killed the circuits and discovering there are others from who knows where that are still live?

I think this is a really poor design, but am not able to locate a code section to prevent it. Thanks again for your help,

Radar
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