ECN Forum Forums Code Related Discussion NEC & other Code issues Branch circuits from different panelboards in same conduit

If you are worried about power from one meter going down, why not run power from both to a transfer switch and then hit the lighting. I think this would be a better solution.

I know that this sounds somewhat unorthodox, but what about using NM-B inside the conduit?

Since you are going to be alternating fixtures, you could pull the cable _through_ every other junction box, and never have conductors from different systems exposed in the same junction box. This would seem to eliminate the problem of accidentally mixing conductors from different panels.

-Jon

Yep this would be a 230.2E requirement if you are allowed to do it. (If it is two services!? You should check that "Special permission" before you build it...) And if it is allowed, still a bad idea, (from two services, especially if not located together.) its not like two different systems of different voltages. You would need the signage to let you know there were two sources... See 225.37

Although these would be two different systems, and need to be identified as such. That means Neutrals and Grounded conductors to identify "system" if in the same conduit, or boxes. Although they might be the same voltage, if they are on different transformers, they are different "systems".

A while back I did a resturaunt with 4 different transformers to 8 panels, all same voltage. It was easier to run all the circuits together. So I got rolls of all my colors... ABCN with black stripe, ABCN with red stripe, ABCN with blue stripe, and no stripes. (The black, red, and blue were slightly different than main color with contrasting boarder.)

My wife works at a disaster control center, and it has several services, and generators all right next to eachother. And a really interesting array of transfer switches. All can be switched to different loads. And it can shed non-critical, all the critical stuff is on UPS. If the door wasn't always locked, I'd get a picture... But it has a huge warning on the door, "Authorized personell only - This facility powered by multiple sources"

Are you marking your own neutrals in some way? Is white THHN available in striped varieties? Not in my area, at least off the shelf. The mistakes happen when care is not taken in labeling each end of wires. This thread has me wondering what is available for neutrals from the factory.

The Romex in the conduit idea seems to me like it would add more difficulties than it would help, since space and code issues limit such installations severely.

One point worth noting here: This is a design / build contract, and the bid documents described basically what we want (the alternating panel circuits on adjascent fixtures idea) without much guidance on just how to design it as long as the design complies with all codes & ordinances. In other words, the contractor is free to design this any way he wants, as long as it meets the performance criteria and is code compliant.

Any design interference from us regarding specifics of his design would result in a contract change. If we now tell him to install separate conduits, or install NM inside the conduit, or whatever, we are changing the contract from the original condition, and affecting his cost base.

OK - so here's another question: NEC 700-9(b) states that wiring from emergency source to emergency load shall be kept entirely separate of all other wiring, other wiring shall not enter the raceway, etc (paraphrased). The obvious exceptions are inside transfer switches, exit or emergency fixtures, light outlets for exit or emergency lighting, etc.

The question is this - in this example, if the branch circuits feeding these lighting units are emergency circuits (at both panels), which are on different meters, and therefore different systems, can they be mixed as proposed above, or must they be kept separate according to 700-9(b)?

Thanks again for all the great replys,
Radar

Radar,

I am just going to repeat you to make sure that I understand where you are coming from.

You (your company) has a contract with a sub, and the sub has the leeway to do 'anything' as long as it meets both the performance criteria _and_ code. The sub has come to you with a proposal which, as far as you know, meets both the performance criteria and code, but does so in a fashion that you are leery of. I presume, then, that you want to achieve one of the following:

1) Find a code reference that makes this proposed design untenable, so that the sub simply can't do it the way that you don't like.
2) Find a method that is the equivalent of what the sub is proposing, but addresses your safety concerns.
3) Find a method that is almost the equivalent of what the sub is proposing, with a slight change in performance criteria that will be easy to negotiate.
4) Decide that you can't force this issue and give up, but at least you know that you tried.
5) Decide that you can't force this issue and re-negotiate a different set of performance criteria with the sub so that they have no reason to use the design that you don't like.

IMHO, your best bet is option 3. I do not see a _significant_ hazard in this installation, as long as the wires from the two different systems are very well segregated. If the conductors from system A simply pass through the JBs for system B, and vice-versa, and if the colors for system A and system B were easily differentiable, then the chance of error will be very slight. Since the sub has no reason to cut the wires from one system in the JB of the other system, this is not going to be a significant performance requirement. However I think that you could only make a code case for identifying separate neutrals.

Identifying _all_ of the wires is IMHO a small performance change. I suggested using romex as a _cheap_ way of identifying all of the wires; but perhaps one could use E57's technique of using custom colored wires, or perhaps pre-twisted wire sets. This sounds like a large enough job that the cost of custom colored wire would be a small premium; in fact you might consider doing the _entire_ job with different colors from each supply. Since this is a change in the performance criteria, I'd presume that you would have to negotiate it, and would have eat the materials cost increase. But I'd think that the cost increase is probably slight.

These latter approaches would result in essentially the same labor as currently proposed. Wire manufacturers can easily make different colors or standard colors with custom striping, and can also easily duplex/triplex/quadruplex your conductors. If you absorb the change in materials cost, this might be very easy to negotiate with the sub.

-Jon

Just to clarify a bit, I currently work for a public agency (quagmire, doonboggle, etc) and we are the customer in this case. We contract with a GC for the design/build work, and the GC's electrical subcontractor is the topic of this thread. They're not our subcontractor per se'.

Our preference would be for the contractor to run one conduit with it's associated wiring from one of the panels, with J-boxes at every other light fixture; and another conduit with it's associated wiring from the other panel, with J-boxes at the remaining every other fixture location. Our problem is that we did not communicate our preference, only the requirement that every other light be connected to one panel, the remaining to the other panel.

Radar

A clarification: If the wiring from the two different panels, are indeed from seperate system transformers, then ALL of the wiring needs to be identified to each system. Neutrals, Phase, and control/switching too.

See 200.6D for neutrals, and 210.4D


The way I have understood this, is that identification is required for each system, not just when they are of a different voltage. Like if you have 120/208, and 277/480 in the same conduit, the same would be true for two different systems of 120/208, or two different 277/480's. This reduces the chances of connecting them, and coming up an 8-wire some weird voltage system. As they are two seperate voltages even if they are the same! What voltage do you get from A1 - A2?

And yes, striped wire is the best way I know of doing this. I get it for the same price as I do regular wire, just have to wait longer for it. If in a rush I get NAILED on shipping though.

Now no one has brought this up... How are these two systems or even if the are just different panels bonded together? The conduit with the lights on it? A water line?

I beleive they need to be grounded at the same place and be sized from Table 250.66.

Now wait... The grounds for each service, from seperate power stations, are MILE APART?! Hope the guy putting the coupling for this together has a WILL. As reguardless of bonding, your lighting conduit will be a parralel path to ground for each service, and likewise the bare-handed guy putting it together.


[This message has been edited by e57 (edited 06-27-2005).]

[This message has been edited by e57 (edited 06-27-2005).]

Good point, e57!

As you suggest, having them bonede at the same point is a way to do it.
So would having them tied to the same "ufer" or grounding grid.
Or, I think simply running a #8 bonding wore panel-to-panel would meet the requirement. Or- maybr not! Do we need to protect both services from lightning if they are far enough apart?

Reno you chimed in there wile I added/edited that last parragraph.