[RE-wrenches] Module grounding requirements

[Drake Chamberlin]

Hi Dick,

The methods of array grounding that I've used are WEEB bonding 
device, or weather resistant grounding lugs screwed to the array 
frame or bolted to array frames, using a star washer to dig into the 
anodized aluminum frame.  The lugs are connected together by a copper 
ground wire, which may be smaller than number 6 if mechanical damage 
is not an issue.

690.43 only states:

"Devices listed and identified for grounding the metallic frames of 
PV modules shall be permitted to bond the exposed metallic frames of 
PV modules to grounded mounting structures. Devices identified and 
listed for bonding the metallic frames of PV modules shall be 
permitted to bond the exposed metallic frames of PV modules to the 
metallic frames of adjacent PV modules.

What I've learned, on this list over the years, is that anodized 
aluminum can develop a resistive coating, so that some method of 
digging into the aluminum, or having a  screw threaded into it, must 
be utilized to insure good bonding."

An engineer, on a job recently, did not require all the aluminum rail 
pieces to be bonded together, since they were bolted together.  This 
seems consistent with 609.43.   Additionally, to do so on that 
particular huge racking system would have created a lot of 
holes.  But here you have an anodized aluminum rail bolted together 
without this extra bonding.

My understanding is that we are permitted to use lugs, bolted to the 
module frames, utilizing a star washer, rather than having a screw 
thread into a hole.  This method is certainly permitted in electrical 
bonding in general, with or without the star washer. I don't know of 
any requirement, for any other anodized aluminum electrical 
equipment, to be bonded in this special manner.


Question  # 1:  Where in the code does it say we need to bond PV 
systems in this particular manner?  250.136 (A) permits metal 
equipment bolted together to be considered bonded.  Are the array 
frame bonding methods a UL requirement?  If so, is there a place we 
can read the actual wording?


Question # 2:  If a star washer is sufficient to bond a lug to a 
module, why is it not sufficient to bond two modules to each 
other?  Or, is a star washer not permitted, even though inspectors 
accept them.  Where can we read what is acceptable?


I'd like to see the wording of the requirement for the extra bonding 
of PV modules.  Maybe I'm missing something obvious, but I don't find 
the requirement spelled out, although do routinely meet it, at least 
as I understand it.



Thanks,

Drake


At 09:25 AM 1/7/2009, you wrote:
>Hi Drake,
>
>Could you please elaborate?
>
>Dick
>
>Dick Ratico
>Solarwind Electric
>Bradford, VT
>
>
>--- You wrote:
>Hi William,
>
>So is there no document we can read that delineates the actual
>requirements?   The standard methods of module bonding that we use
>don't always seem logical.  Engineers on a recent job had similar feelings.
>
>Drake
>
>
>
>
>At 03:07 PM 1/6/2009, you wrote:
> >Drake:
> >
> >Listed equipment must be installed per the manufacturer's
> >instructions.  Listing agencies require grounding by a specific
> >process to replicate circumstances that occur when the product is tested..
> >
> >William Miller
>
>Drake Chamberlin
>Athens Electric
>OH License 44810
>CO License 3773
>740-448-7328
>740-856-9648
>
>--- end of quote ---
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
740-856-9648