Branch circuits of 120/208v and 277/480v in same junctio

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wwebb

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I have assumed many things throughout the years concerning wiring methods. When apprenticing in the trade, I learned (I thought) many things from Inspectors and Supervisors in the electrical trade. I am quite familiar with the NEC (or at least I thought that I was) and I am now stumped.
I have always assumed that when installing branch circuits in a facility which contains 120/208 3phase as well as 277/480v, 3phase systems, that you could not junction circuits from both systems in the same junction box. I am now searching, unsuccessfully, the 2002 NEC for a Code to support this assumption. I have not been able to locate this.
The only item I have found related to this is 300.3(C)(1), which seems to allow this type of installation.
Have I been making the wrong assumption, or am I just a little "brain dead"?
I know that we are always learning, but this is nuts.
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

The only issue is voltage between adjacent devices, which can be found in 404.8 (off the top of my head).
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

As long as the insulation on the conductors of the 120/208 and the 480/277 are rated at 600v for the maximum circuit voltage, they can share the same raceway or junction box.
300.3c

[ October 22, 2004, 04:04 PM: Message edited by: jap2525 ]
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

Sections 200.6(D) and 210.4(D) may also apply, however, neither of these sections prevent the instsallation you are questioning, they just provide requirements for when you do.
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

I don't have a reference handy, but I seem to remember seeing an illustration in the handbook that showed how the grounded conductors of circuits of different voltages that are in the same j-box have to be marked as distinct from one another. If they have this requirement, I think it's safe to assume that it's permissible to have circuits of different voltages in the same j-box.
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

I do not think that NEC prohibits this, as long as other Code rules mentioned in the above posts are followed. But we consider this as not a good design practice & do not do it, at least in new work for branch ckts.

Big feeders in big pullboxes, might be a little different story.
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

Originally posted by jap2525:
As long as the insulation on the conductors of the 120/208 and the 480/277 are rated at 600v for the maximum circuit voltage, they can share the same raceway or junction box.
300.3c
Click to expand...
i thought they had to have the same temp. rating to share the same raceway.
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

The conductors do not have to be the same temp rating, however when derating for conductor fill then different temp ratings would complicate the derating.
277/480 and 120/20 or 240 certainly can share the same enclosure, box or raceway.
However they have to be identified as to the branch circuit and source. If grounded neutral conductors are present then they have to be individually identified, first is white or gray, second has a stripe not green see 200.6 (D)

And a change in the 2005 NEC now requires the ungrounded conductors to be indentifed by system and the system posted at each panel. see 210.5(C)
You can use pink/blue/black for 277/480 if you want, as long as you maintain the identification colors throughout.
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

And a change in the 2005 NEC now requires the ungrounded conductors to be identifed by system and the system posted at each panel. see 210.5(C)
Click to expand...
But we lost the requirement that was in 210.4(D) that required multiwire circuits to be identified as to both phase and system. Now they are only required to be identified by system. You could use blacks for all of the phases in a 208/120Y volt circuit and reds for all of the phases in the 480/277Y circuits and be in compliance with the 05 code. That would have been a violation in the 02 code. I think that the code took a step backwards here.
Don
 
Re: Branch circuits of 120/208v and 277/480v in same junctio

Don I'd agree that is a big step backwards. I liked 210.4(D) by the 2002 code.

Al
 
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