Rooftop wiring [RE-wrenches]

[bob ollerton]

Somehow a part of my email on this got dropped, sorry.

So I need to add hat Cad plated hardware is thought to be the least reactive
with Aluminum and still have corrosion resistance.

There are Aluminum nuts and bolts that would be less reactive with the
mounts, but would probably corrode together when exposed to nature, so not
very useful. These are sometimes used in aircraft where weight is a real
problem but they are expensive and don't have the structural strength of
steel.

This is probably not the biggest problem to worry about when installing
panels, and like many things there is a tradeoff with where the corrosion is
and its effect.  Being able to take a nut of a bolt 10 years later might be
the real priority.

You can almost eliminate the dissimilar corrosion  if you put some kind of
insulating washer between the stainless or Cad plated steel part and the
Aluminum.  On Aircraft (restoration) we use mylar cut to shape of the steel
part being mounted against aluminum, or easily obtained nylon washers under
nuts and bolts.  And one last point is that the aluminum alloys used in
industrial products is less reactive and vulnerable to corrosion than almost
all the alloys used in Aviation.

Last but not least, I have a chart of relative corrosion of dissimilar
metals that I got from a class at the Smithsonian, I will dig it up and type
in in and post it here in hopes its usefull to someone.


bob.


----- Original Message -----
From: "Bill Brooks" <billbrooks7 at earthlink.net>
To: <RE-wrenches at topica.com>
Sent: Thursday, April 11, 2002 2:48 PM
Subject: RE: Rooftop wiring [RE-wrenches]


> Is that true? Maybe if the Zinc-plating stays in place, but experience
says
> otherwise--I'm sure other wrenches have observations on this.
>
> Bill.
>
>
> -----Original Message-----
> From: bob ollerton [mailto:lizard at mcleodusa.net]
> Sent: Thursday, April 11, 2002 12:34 PM
> To: RE-wrenches at topica.com
> Subject: Re: Rooftop wiring [RE-wrenches]
>
>
> If you are looking to protect the aluminum, Zinc (galvanized hardware) is
> less reactive with Aluminum than stainless steel in wet environments.
>
>
>
>
> ----- Original Message -----
> From: "Bill Brooks" <billbrooks7 at earthlink.net>
> To: <RE-wrenches at topica.com>
> Sent: Thursday, April 11, 2002 11:57 AM
> Subject: RE: Rooftop wiring [RE-wrenches]
>
>
> > Kurt,
> >
> > The screw needs to be stainless so it will not galvanically corrode with
> the
> > aluminum. Some manufacturers provide these screws, some do not. The main
> > reason the code requires attachment to each module is because the
> > manufacturer tests the module at UL with the grounding point shown on
the
> > module. Because they do not provide any other direction on acceptable
> means
> > of grounding, or test those alternative means. This is a major hastle
for
> > rooftop installations because the grounding systems were never designed
to
> > be easily installed on roofs. They were designed for open rack mounting.
> >
> > This is an area where installers are going to have to make their voice
> known
> > to manufacturers so that they provide us better products for grounding.
> >
> > Bill.
> >
> >
> > -----Original Message-----
> > From: sunwise at cheqnet.net [mailto:sunwise at cheqnet.net]
> > Sent: Thursday, April 11, 2002 11:10 AM
> > To: RE-wrenches at topica.com
> > Subject: Re: Rooftop wiring [RE-wrenches]
> >
> >
> > Brad Bassett wrote:
> > >
> > > Another question I have is how often do other installers use a ground
> > > wire to every module, or a star washer on each module and ground the
> > > rack? What's common practice for grounding arrays?
> >
> > Hey Brad,
> >
> > I think code says you're supposed to hit every module and I do the
> > mast/rack as well.  I have heard that part of the reason each module
> > needs its own ground connection has to do with the resistance of the
> > anodizing on the AL frames (is the star washer suposed to dig in past
> > the anodizing?).
> >
> > I use self drilling/self tapping, hex-head screws that easily drive into
> > the panel's designated point of ground on the frame, but have heard that
> > such screws do not meet code, any additional comments?
> >
> > Kurt Nelson
> >
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