[RE-wrenches] Over-torquing Module Clamps?

[August Goers]

Hi Corey -

For many years we used Pro Solar racking and Unirac Solarmount and
tightened the clamps with impact drivers. At some point maybe roughly 8
years ago, Unirac switched its mid clamps to stainless steel self grounding
clamps with teeth to bite into the module frame. We continued to use
impacts with no issue. Then, starting around 4 years ago, we started to
have module glass failures with our SunPower commercial systems and these
Unirac clamps. We immediately switched to torque wrenches for tightening
the clamps. However, the failures continued. My guess is that the poor
design of the Unirac mid clamps in conjunction with thinner “weaker” module
frames exasperated the issue. We now have stopped using those mid clamps
and continue to hand tighten all clamps. We primarily install SunPower, and
their residential module frames have a lip so all the pressure from the
clamp doesn’t go to the glass.

Getting to your question - what kind of mid clamps do you have? If they are
aluminum, there may be less risk than the stainless clamps. I would be
worried that the process of loosening and then re-tightening might cause
more damage than good if there aren’t any problems that have occurred to
date. It’s a good question.

August
Luminalt

On Fri, Sep 3, 2021 at 12:06 AM Corey Shalanski <coresolar at gmail.com> wrote:

> Wrenches,
>
> (This question actually does refer to the proper use of 'wrenches'...)
>
> While inspecting some recent work from one of our contractors, we noted
> that the PV module clamps had been torqued to ~150% of the racking
> manufacturer's specified value. My question is whether that might have any
> detrimental effect on the modules (frame, glass, cells, seal, etc) and
> whether it would be worth loosening the clamps and re-torquing them to the
> proper spec? For reference, 224 modules are installed.
>
> We were made aware that the contractor used an impact driver on the
> clamps, which accounts for the excessive torque applied. I definitely
> understand the temptation to use an impact driver for just about
> any hardware that needs turning—but my understanding is also that impact
> drivers are generally incompatible with machine screws. So my other
> question to the group is whether anyone has had success in dissuading
> subcontractors from using impact drivers so liberally on project sites? Any
> advice is appreciated.
>
> --
> Corey Shalanski
> Jah Light Solar
> Portland, Jamaica
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> --
August Goers
Luminalt
o: 415.792.6666
m: 415.559.1525
august at luminalt.com
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