[RE-wrenches] Rail concerns (was: Top of POST mount)

August Goers august at luminalt.com
Wed Mar 23 07:09:41 PDT 2011


You definitely have a point from a basic engineering point of view that
bolts through the module bottom holes is technically the most robust option.
However, the main racking companies have been selling top down clamps for a
very long time and the two big ones, Unirac and Pro Solar, haven't changed
their design for a long long time as far as I can tell. I tend to like Pro
Solar's clamps, especially the end clamps, a bit better than Unirac's but I
have to believe that if there was a problem that these companies would be
the first to change their design. Modules flying off the rack or roof is a
very bad thing. Some of you may recall the modified hex bolts that Unirac
was shipping for a little while a couple of years ago. They definitely
weren't good but Unirac got right on it and we had to switch out each and
every one that we had installed... That said, if you're talking about pole
mounts and other types of racking where you can get underneath easily then
why not just use the bottom holes.



-August



*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Jason Szumlanski
*Sent:* Wednesday, March 23, 2011 4:40 AM
*To:* RE-wrenches
*Subject:* Re: [RE-wrenches] Rail concerns (was: Top of POST mount)



I tend to agree about the clamps, and in a case like this where there is
little risk of an expensive mistake with a voided warranty, I would actually
drill holes in the frame and use bottom clamps in addition to top clamping.



Jason Szumlanski

Fafco Solar





*From:* re-wrenches-bounces at lists.re-wrenches.org [mailto:
re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *William Miller
*Sent:* Tuesday, March 22, 2011 5:48 PM
*To:* RE-wrenches
*Subject:* [RE-wrenches] Rail concerns (was: Top of POST mount)



Friends:

When installing modules on extruded rail systems, I worry that any vibration
or motion could loosen top-down clamps.  Unlike bottom-up systems that
install with tried-and-true bolts and lock washers through captive holes,
clamp systems seem less "positive" in holding capability.  If one rail in
the proposed design moves in relation to the other, the clamps could loosen
and the modules could eventually slide right off the rail.  It appears that
wind turbulence could rock the modules in the proposed design, there is a
lot of leverage for that.  This might loosen clamps.

I hesitate to design my own racking.  Small business management is all about
controlling risk.  I do not want to be responsible for damaged modules if my
design fails.

At least one local AHJ forbids home-brew racks for a permitted system.  I'm
not sure I support that restrictive approach.  I might suggest allowing them
for owner-builder systems where the home owner assumes the liability.  For
myself, the remaining tasks associated with installing a system properly
have enough pitfalls without me playing structural engineer.

And lastly, it is my understanding that Solar World had temporarily
abandoned mounting holes in the back rails of their new "Plus" modules (my
quotes) and even abandoned the flanges altogether.  According to what I
heard, industry pressure forced them to add them back in, but as an option.
This is third-hand knowledge, but I do know that removing the option to
mount panels with through bolts would be a big mistake.

William Miller




Here is my “cobulated” idea, admittedly done this way to take advantage of
parts in stock:

http://www.fafcosolar.com/download/402/Cobulate.pdf
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