[RE-wrenches] Cable tray

Mon Mar 25 22:15:11 PDT 2013

William,

I would strongly disagree that conduit is tried and true on rooftops. I have
rarely seen good conduit runs on rooftops. Most electricians have no clue
how to work with expansion joints. Conduit on rooftops is a bad idea in
general. Most conduit runs in big buildings are all done indoors for good
reason. We are the crazy people doing things on the roof. 

The sooner we get away from conduit-particularly for long feeder runs-the
better.

In Europe they don't have problems with their rooftop wiring systems because
everything is in tray.

For those that don't allow cable tray for anything less than 1/0, just
remember that if it isn't called cable tray, then 392 doesn't apply. The NEC
would allow us to use treated lumber in place of cable tray. This makes no
sense.

We did some research on the origin of the 1/0 requirement, and it is ancient
and no longer relevant. Just because it is in the code, does not mean it is
correct. That's why we try to fix it every three years.

Bill.

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William
Miller
Sent: Monday, March 25, 2013 9:30 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Cable tray

David:

Of course, I understand that you are not saying we can willfully disregard
the Code in anticipation of future clarification.  I was just extrapolating
on your idea.  

If we want an exception based on a predicted update in the code, we are at
the mercy of the AHJ who may or may not be convinced.  I think most AHJs are
willing to diverge from the Code in a more strict interpretation, but not
the reverse. Right now, as I read it, unless the leads are 1/0 or larger, we
are forbade.

I treat PV systems like rooftop AC units.  The voltages and currents are
similar, if not more severe.  I don't believe you could or should run power
to a rooftop AC unit in cable tray.  Conduit is a tried and true practice
and I recommend it.

William Miller

At 06:01 PM 3/25/2013, you wrote:

Ouch. I promise I'm not advocating for anything like that. What I may be
missing is the Code reference that says "no cable tray on roofs" or similar.

There is so much room for improvement in wire management practices, that
being able to use cable tray seems like a step forward. I understand some
jurisdictions do not allow it, but it appears as though Code changes were
made specifically to address this. It's boring stuff, but you can read the
explanation of the Code changes in the ROP and ROC documents. 

The Code changes a lot with regards to PV system, and Article 690 is more
fluid than other articles. Some of this is the Code trying to keep up with
technology. In other cases the Code evolves based on new applications for
existing products. Often it changes because some areas of the Code are
confusing for electricians and inspectors alike. If the new Code language is
more clear in its intent than previous versions, some inspectors are willing
to let installers build to the most current standard.

That's all I'm advocating for: Trying to understand how the minimum
requirements outlined in Code evolve over time so that you can have a
friendly and informed conversation with your AHJ over a donut. 

On Mar 25, 2013, at 6:26 PM, William Miller wrote:

David:

This is great news.  Now, whenever I want to do something that is prohibited
by code, I can just say that the Code Making Panel is gonna correct that
pesky code section (insert your problem citation here) any day now, so I
might as well be allowed to do whatever it was I was fixin' to do anyway.
Unless I am missing something...

Thanks!

William Miller

PS:  Just kidding.  Hope no offense is taken.

wm

At 03:46 PM 3/25/2013, you wrote:

So if you ever get called on 392.10(B)(2), I think you can point out that
the Code Making Panels have been busy clarifying that cable tray is okay for
source circuit conductors. Unless I'm missing something....

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Miller Solar
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