Sharp modules [RE-wrenches]

[Bill Brooks]

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William,

Matt raises an important issue that I don't hear the conduit proponents
mention very often. That point is that many module manufacturers that offer
junction boxes do not have conduit ratings on their junction boxes. Has
everyone checked the conduit rating of their junction boxes? (Shell is the
only one I know for sure--possibly Kyocera as well) Just because a junction
box has an appropriately-sized knockout does not mean that it is rated by UL
to receive conduit. I have seen many examples (e.g. BP Solar, Solec, etc...)
where the junction boxes worked loose because they were exposed to the
normal stresses that thermal cycling flex puts on junction boxes.

Long before MC Cables were available, I supported the idea of multiconductor
cables (TC) being run between modules to comply with the "no conduit" issue
of most junction boxes. TC has its own problems in that it is not fire
rating (can't run through the house) and I have found that squirrels like it
(over 20 burned out shorts in a 3 kW array from squirrel damage), but I have
to ask if conduit is so much superior given the broken junction boxes laying
on the roof at 600Vdc.

USE-2 seems to be the best thing going right now. The biggest drawback to
USE-2 is that it is difficult to keep neat and protected from physical
damage--many installers connect the MC connectors and drop them on the
roof--just as bad as squirrels on TC.

For those that don't like plugs, I would like to see a TC that has rodent
inhibitors in it. I'm sure it must be available somewhere--anybody know of a
source?

Bill.


-----Original Message-----
From: Matt Tritt [mailto:solarone at charter.net] 
Sent: Tuesday, March 01, 2005 10:02 AM
To: RE-wrenches at topica.com
Subject: Re: Sharp modules [RE-wrenches]

  This is only the case if you don't make the run to the combiner with MC 
cables. We have had O problems in using the MC system as designed (and 
employed all over the world) though. I know that there is a divergence of 
opinion on the use of exposed cabling in our business and I have had many 
converstaions with installers in the US and elsewhere about the pros and 
cons of both methods.

  My conclusion, which will not be shared by one and all, is that either 
method can be easily compromised by mischievous intent or honest accident. 
As a matter of fact, the only problems I've ever personally encountered with

panel wiring have been done in flex PVC conduit. In one case, a guy called 
me to look at a sytem installed by others that had stopped working properly.

I discovered that someone (no-doubt a young boy) had pulled hard enough on 
inter-connecting conduit to break the j-boxes loose, pull the conduit from 
the adaptors and rip the wire ends from their connections on a pair of 
panels. The panels were also badly damaged in the process.

  Another situation I encountered was with a job I subbed-out to a competent

electician who used flex conduit to connect panels to inverter on a pair of 
tracking systems. The conduit had been incorrectly cut and routed which, 
because of the semi-flexibility of the material and the way it was fixed, 
caused the tracker to bind, which pulled the conduit loose, damaged a J box 
and blew a fuse in the tracker.  Since I sold the system, I had to fix the 
systemic problems with this install so it sticks in my memory. I also have 
to admit that back in the "old days" it was common practice to do all module

inter-connections in exposed THHN and/or tray cable. I recently re-visited 
an install I helped do in 81 that was still going strong in spite of the 
crappy looking module inter-connects. No cracks in the insulation, no 
shorts - just several cases where the rubber plugs that Arco used to provide

on their J boxes had fallen out and been replaced with hornet nests. Gulp. 
These were all 12 volt systems of course but still have plenty of potential 
for disaster.

  As to Todd's comment on the Cheese Factor of exposed cables, if done right

it doesn't Have to look tacky, but it does take some time to tidy things up 
and get everything the right length for the drip loop. (I'm only referring 
to pole mounted systems here, by the way).

  An over complex reply to a nice, simple question if there ever was one!

  Matt T
 

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