Module grounding revisited [RE-wrenches]

[William Miller]

Allan and Wrenches:

Thanks, Allan, for contacting John.  I apologize for wasting all of your
time going off half cocked on this idea.  I try to read the Code Corner
faithfully, but I must have missed this one and it sounds like others did
as well.

The lesson learned is that the NEC is not a stand-alone document.  I will
be researching more reading of the UL documentation in an effort to be the
best PV installer possible.  Anyone suggest any other texts to be
acquainted with?

It sounds like this idea is pretty well dead and that we've been doing the
right thing all along, although the corrosion issue with copper against
anodized aluminum has yet to be resolved. I will experiment with SS
washers, although many grounding screws may be too short to include two
washers.

On the positive side, we got to learn more about ground wire sizing and
grounding electrodes.  Thanks for all who contributed.

William Miller




At 09:38 AM 10/30/02 -0700, you wrote:
>Here's John Wiles' response to William's question on rack versus module
>grounding:
>> Allan:
>>
>> No.  This comes up every year.  I address it at least once a year in
>> Code Corner.  I wish more people would read it.
>>
>> Early in the days of PV (early to mid 1970's), Jet Propulsion Labs,
>> Underwriters Laboratories (UL) and the PV module manufacturers
>> determined through extensive and widespread testing and field
>> experience that it was not possible to obtain adequate module
>> grounding through the mounting bolts used to fasten the module frame
>> to a grounded mounting structure.
>>
>> Aluminum oxidizes very easily and quickly.  The oxidation is an
>> insulator.  Anodized modules (brown or other color) are also
>> insulated by the anodizing.  These insulators are hard to break down
>> and hard to stay broken down with normal mechanical fastenings of
>> module frames to module racks.
>>
>> For this reason, UL Standard 1703 requires that a specific grounding
>> point be identified and hardware be supplied for each module to
>> ensure that the proper grounding is made and maintained.  This is
>> usually a self tapping screw made of stainless steel that must cut
>> 2.5 threads in the aluminum module frame.  Some modules have threaded
>> stainless steel inserts to meet this requirement.  UL tests this
>> grounding connection for continuity and voltage drop with current
>> injection to all other parts of the module frame and to any other
>> exposed metal on the module.
>>
>> The NEC requires that all equipment be installed in full compliance
>> with any instructions or labels furnished with the product.  The
>> module instructions and the marked green grounding point on the frame
>> override any general requirements found in either Article 690 or in
>> other sections of the code.
>>


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