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#178989 - 06/20/08 02:26 AM Circuit conductor grouping
jes Offline
Member

Registered: 07/12/02
Posts: 103
Loc: CT
HID lighting installation done years ago...1980's
All 208V ckts with 5 - 2.5A HID fixtures per 20A ckt, run in armored cable from common switching location (2 pole switches) to junction boxes in overhead where it is broken out into each light string.

The circuits in the armored cable are each run with like colors from TWO cables... 2 reds, 2 blacks, 2 whites. So, 2 - #12-3 armored cables carry 3 circuits with one phase of each circuit in each cable. Phases are NOT the same as it is a random pick of breakers in the three phase distribution panel.

This installation has been prohibited by the NEC for as long as I have Code books. (300.3(B) in the '05 Code)

Has anyone seen an actual problem in an installation like I have described?

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#178990 - 06/20/08 04:41 AM Re: Circuit conductor grouping [Re: jes]
Brian_John Offline
New Member

Registered: 05/14/07
Posts: 7
Loc: Leesburg, VA
Are you saying the 12-3 has an "A" phase from one panel and possible a "B" phase from another panel?

This would result in neutral circulating current between the two panels.

Are the panels off the same transformer?

While not compliant, it would not result i induction issues.
IF I AM READING YOUR POST CORRECTLY.

But I would suggest rewiring to correct the issue.

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#178992 - 06/20/08 07:19 AM Re: Circuit conductor grouping [Re: jes]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
I think he is describing two things that were done ...

I think he is saying that every box / fixture receives two pieces of MC. The fixture is then hooked up to, say, the red wire from each cable. Back at the panel, one red is landed on, say, phase "A" while the other red is landed on phase "B".

From a code perspective, there is no requirement to adhere to any color coding. So, having the reds land on two different phases is not a violation. A maintenance / troubleshooting nightmare, sure ... but no violation.

I don't think there are any neutral currents involved at all.

There is a violation of the code requirement that all conductors be run in the same conduit or raceway. I believe the reason is a fear of inductive heating of the raceway itself.

Our OP is thus presented with an old installation that has been working fine for years, and is wondering just how important it is to fix it. This, naturally, would be an involved and disruptive task.

I say: Do it. I suspect that, along the way, other, more critical errors were made. The method smacks of 'self taught, well meaning handyman.' I am curious as to the use made of the white and green wires in those cables.

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#178994 - 06/20/08 08:17 AM Re: Circuit conductor grouping [Re: renosteinke]
Brian_John Offline
New Member

Registered: 05/14/07
Posts: 7
Loc: Leesburg, VA
 Quote:
The circuits in the armored cable are each run with like colors from TWO cables... 2 reds, 2 blacks, 2 whites. So, 2 - #12-3 armored cables carry 3 circuits with one phase of each circuit in each cable. Phases are NOT the same as it is a random pick of breakers in the three phase distribution panel.


Need clarification here.

Are there 3 circuits on two 12/3 MC's For example Black, black one circuit, red, red one circuit and white, white one circuit?????

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#179002 - 06/20/08 03:50 PM Re: Circuit conductor grouping [Re: Brian_John]
electure Offline

Member

Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
Instead of speculating, perhaps the Original Poster could clarify things.

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#179004 - 06/20/08 04:17 PM Re: Circuit conductor grouping [Re: jes]
jes Offline
Member

Registered: 07/12/02
Posts: 103
Loc: CT
OK, to clarify a bit...
ALL circuits are from the SAME 3 phase loadcenter fed from the SAME service fed from the SAME transformer. There is NO neutral involved. In fact there are no circuits with neutrals landed in this panel. ALL 208 volt 2 wire lighting circuits using 2 phases.

Two #12-3 AC (not MC) cables carry three circuits fed from separate 2 pole breakers. One circuit uses the BLACK from one AC cable and the BLACK from the second AC cable. The same is true for the REDs and the WHITEs.

At the opposite end of the run (100+feet) there is a junction box where the BLACK circuit is sent off via EMT to one string of lighting. The same for the other two colors.

The phases used are random in the loadcenter with other circuits but I am relatively certain that at least 2 and likely 3 phases are present in both AC cables.

I am wondering if anyone has SEEN a problem related to improper grouping of circuit conductors like this.

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#179006 - 06/20/08 05:17 PM Re: Circuit conductor grouping [Re: jes]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Looking out my window, my view of traffic lets me see numerous cars go by in excess of the posted speed limit. Seems nearly everyone goes 'a little bit' faster.
I have yet to see an accident that could be attributed to going only a few miles over the 'limit.'

Still, that doesn't make it right. Nor will it get you off a ticket, should you get one.

I have not seen a problem that I could attribute to having the wires distributed as you describe. Indeed, I have never seen such a distribution done. Maybe I've been lucky, but every three phase lighting installation I've seen has had all the circuit conductors contained within the same 'wrapper.'

You've got an installation that violates code, and makes things the very devil to sort out. The correct thing to do is to fix it. If that means running another cable, so be it.
My failing to encounter such an installation, combined with the lack of problems on the site, does not make it right. It needs to be fixed.

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