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Joined: Mar 2005
Posts: 1,213
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I inspected a UPS installation yesterday we and filled up 2 sheets of violations. One of which had to do with the conduit; the electrician had installed the UPS rectifier input, bypass input and output cabling in a single 4" piece of rigid conduit. They had also run the UPS alarm cabling through the same conduit. My colleage and I are both certain it's illegal, but couldn't recall exactly WHY- the two inputs (rectifier and bypass) are fed from different transformers, but coming from a common bus. Is it legal to put both of those in a single raceway? Is it legal to put the UPS output cabling in the same raceway as that?

And finally, the data cable they used has no markings on it to indicate voltage rating or that it's class 2 so it's illegal in this case- if it WAS 600V class 2, would it be legal to run it in the same conduit? It's not controlling the UPS, but is taking alarm signals from the UPS ("on bypass") to the wraparound maintenance bypass switch.

2017 / 2014 NEC & Related Books and Study Guides
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The only way this low voltage signalling circuit can be in the same pipe is if it meets the requirements of a class 1 (basically using the same wiring methods as chapter 3). The other requirement is that it is associated with the power circuits it shares a raceway with, but you have that.


Greg Fretwell
Joined: Oct 2004
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As far as running the input, bypass, and output in the same conduit...wouldn't these be Separately Derived Systems? You can run power wires of different systems and voltages in the same raceway. I don't see a code problem with it, though it is a bad design as far as uptime goes.
Mike

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They've got bad practice all over this job, that's for sure! I can't reject this shared conduit unless there's an actual code violation, though. Ah well, I guess I'll be hitting the NEC hard tomorrow morning...

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725 is the most confusing part of the NEC IMHO.
The different interpretions I have seen are even more confusing than the language of the code.


Greg Fretwell
Joined: Mar 2005
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The UPS manual says the alarm & signaling circuits are Class 1, and should be installed IAW NEC Class 1 requirements. NEC 725.26(A) Permits Class 1 circuits to share a cableway with power cables, but only if it's rated for the highest voltage in the raceway. The cabling installed on-site gave no indication of any voltage rating.

Also, the power cabling they installed was labeled "TW75" What the heck is TW75, Canadian THW?

NEC 250.20(D) FPN No.1 notes that on-site generators are not considered separately derived if the neutral is solidly interconnected to the service-supplied neutral. As this is the case with this UPS, I do not believe it would be considered separately derived.

Last edited by SteveFehr; 04/24/07 07:17 AM.
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I guess you ae left with the question of the rating of your LV cable. The general rule with inspectors is, if it isn't labelled it does not have a voltage rating.


Greg Fretwell

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