rooftop wiring/grounding [RE-wrenches]

Sat Apr 13 09:21:53 PDT 2002

Colleagues:

Why are so many installers against the use of conduit?  I really like using
1/2" non metal liquid tight to interconnect modules.  At each rack, I
connect to a PVC J-box and transition to schedule 40 PVC.  Here are my
reasons for using conduit:

-I know there is a hair splitting compliance question regarding temperature
when using non-metal flex, but I've never seen the flex fail or degrade.
-In just about any other commercial/industrial wiring situation, wire is
protected by conduit.
-Conduit has many provisions for attaching to supporting structures.  I use
a 1/4" beam clamp attached to a mineralic conduit hanger to attache to rack
rails.  I use a beam clamp to attach PVC J boxes to rack feet and
transition to PVC.
-PVC is listed as sunlight resistant.There are many UV resistant coatings
to protect PVC from discoloration.
-Non metal liquid tight conduit is water tight.
-Conduit protects wire from abrasion.
-Conduit allows one to wire in series, parallel or any combination.
-Conduit allows one to put more than one wire into a knockout.
-Conduit can be used to route a ground lead along with the current carrying
conductors.
-Non-metal flex and schedule 40 PVC is readily available and inexpensive,
as is THHN stranded.
-When using conduit, one can change out wiring if there is a failure or
change in design.

William Miller

At 10:45 PM 4/12/02 -0400, you wrote:
>For wiring both between modules, as well as longer runs to a central 
>combiner box, we are working with the multi-contact cables, made for each 
>project for us by Kensington. To keep them in some sort of order, or at 
>least away from abraision, we had been simply tie-wrapping to supports, 
>etc., but I've not really been pleased with it.
>
>We are now going to try out some plastic cable tray which we can fasten 
>directly to the horizontal rack supports. This will give us a nice place to 
>tuck all wires, let us get at them if we need to, and should proceed 
>faster. At any rate, it keeps the wires out of harms way.
>
>At the end of the rack, we'll transition to a piece of flex (through a 
>multi-wire gland connector) unless the combiner box is within inches of the 
>end, in which case we would simply let the wires come out the end of the 
>tray.
>
>The idea is to make the roof work fast and easy, and as fool proof as 
>possible. (I can be a pretty good test for that some days....)
>
>We'll let you know how it works after we do a few.
>
>Jeff
>Jeffery D. Wolfe, P.E.
>Global Resource Options, LLP
>A Woman-Owned Limited Liability Partnership
>4 Kibling Hill Road
>P.O. Box 161
>Strafford, Vermont 05072
>800-374-4494 Toll Free
>802-765-4632 Phone
>802-765-9983 Fax
>global at sover.net
>http://www.GlobalResourceOptions.com
>
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>
>
>On Friday, April 12, 2002 12:31 AM, Brad Bassett 
>[SMTP:bsbassett at earthlink.net] wrote:
>> First, I would like to say that I had no intention of denigrating all
>> California solar installers. Now that I've seen the responses, I assume
>> that unprotected home run wiring is not the norm anywhere. That there
>> are installers that do better work than others will always be true.
>>
>> My comment about Washington inspectors has mainly to do with the fact
>> that outside of the cities, the inspection is done by a state agency,
>> and they tend to be consistant sticklers. That's OK if you do it right
>> (and can quote chapter), and have UL listed equipment (no UL = no
>> acceptance).
>>
>> I agree that the wiring between modules is still a concern. I've seen
>> wires sitting on the roof in many installations, and in the back of my
>> mind am thinking that an entirely different wiring method needs to be
>> designed for wiring between modules. The gears are whirring in my mind,
>> maybe someday I'll be able to do something about it. I understand why
>> some agencies are tending toward conduit used everywhere, but this can
>> be quite a bit of overhead if done with conduit said to be rated for
>> that use. And as pointed out, conduit can be poorly installed also. This
>> leads to another question, what are some good methods for supporting
>> conduit on a roof? (I will ask this within our company and get some more
>> answers too, I'm sure)
>>
>> On the grounding of modules, I'm surprised to hear that grounding of
>> individual modules is actually done! I figured this was skipped by most,
>> I guess not. I'm used to working with ASE-300's which make it easier,
>> both because they have a threaded insert in the frame with grounding
>> hardware, and because there are fewer modules for a given size system.
>> (Yes, star washers are made to break the anodized or painted surface for
>> electrical continuity)
>>
>> Brad Bassett
>> Schott Applied Power
>> Tumwater, WA office
>> bsbassett at earthlink.net
>>
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>
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William Miller
Miller Power and Communications
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