Please Read!

[dereckbc]

This is a general question mainly for the inspectors but all comments welcome.

I have been designing DC power plants for the telecom industry for years, and have been aware we play loose and fast with the code in the design. Mostly with de-rating cables such as having as many as 72 500 MCM cables in a cable tray and not de-rating to 310.15 or having space between cables.

I was always under the impression were allowed to do so because we are a utility, designed under engineering supervision, and the areas are only service by qualified personnel. But I always wondered why in some circumstances like telcos that are not a utility and have equipment in public buildings like high-rises ever got away with it.

Well I was speaking with an ole ex-Ma-Bell power engineer who I have a great deal of respect for and who has forgotten more than I will ever know told me I was all wet. He said the reason is after the rectifiers all the cabling is not premise wiring and is considered utilization equipment, therefore the NEC couldn?t say squat about it.

I argued for a moment because I have been busted for it twice; once in King of Prussia and Reston VA. There I had to install multi-layers of cable rack and have 1-inch air-gap spacing, or quadruple the cable count. Wished I had the premise wiring argument under my belt then, I would have played it out in court as the re-do cost over $1M

What do you inspector types think???

 

[BarryO]

Re: Please Read!

Originally posted by dereckbc:
[QB]He said the reason is after the rectifiers all the cabling is not premise wiring and is considered utilization equipment, therefore the NEC couldn?t say squat about it.

So he's saying the NEC doesn't apply to utilization equipment? 'news to me.

 

[esox39]

Re: Please Read!

I install alot of these systems, -48V DC, for the "teleco" industry. Now that there are so many "telco" companies out there, whose to tell who is the "utility" and who is not. What I run into is when inspectors see these systems finished, they are a little overwhelmed by the amount of cables installed, all tied with string in very neat stacks, bent and rolled down the ladder racks. Most have never seen this let alone the amount of grounding involved with the ground field, bonding of everything and anything metal. I believe nothing is ever said because most inspectors don't have a clue on what they are looking at, but is sure looks good when done correct.

 

[don_resqcapt19]

Re: Please Read!

Premises Wiring (System). That interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed, that extends from the service point or source of power, such as a battery, a solar photovoltaic system, or a generator, transformer, or converter windings, to the outlet(s). Such wiring does not include wiring internal to appliances, luminaires (fixtures), motors, controllers, motor control centers, and similar equipment.

I see the rectifiers as a "source of power" and the conductors on the load side of the "source of power" are "premises wiring".
Don

 

[pierre]

Re: Please Read!

I agree with Don and Esox.
The rectifiers can be a source of power or in other words a supply source. The component itself is listed, the wiring is Premises wiring, and depending on the wiring method, it would follow that part of the code.... that being said, doing some of the calculations necessary for cable trays can be a pain in the... Art 392 is almost for specialists.


"I believe nothing is ever said because most inspectors don't have a clue on what they are looking at, but is sure looks good when done correct."

The above scenario either creates a "monster" or a "silent participant".

 

[triphase]

Re: Please Read!

pierre true. If I am "clueless" I make sure We walk it together. I ask a lot of questions. I don't play "dumb" so to speak. If I see any thing ominous, such as derating, sizing, grounding, bonding etc., then "hey" let's research it together and come up with a solution. I know it sounds like a "backwoods" approach but it seems to work out with everyone involved.

 

[mprairie]

Re: Please Read!

Just a non-inspector comment.
Has anyone experienced capacitive influence in parallel runs of DC conductors?
I know I cant use a DC megger on parallel bus bar runs.
This may be where spacing comes into the picture.