[RE-wrenches] Module grounding requirements
Drake Chamberlin
drake.chamberlin at redwoodalliance.org
Fri Jan 9 10:00:04 PST 2009
Hi Richard,
Thanks for responding to my post. It looks like no more responses
are coming in on the thread.
To summarize, it looks like the module grounding methods are not too
clearly spelled out at this time, and that some of the methods we use
could possibly be problematic (I.E. the ground screws used with
lugs). As the code catches up, maybe methods will be spelled out
more clearly.
It seems that the WEEB devices are safe, both institutionally and
technically. Also, the new UniRac self grounding mounts should
provide a good solution. Hopefully, self grounding mounts will
become the norm, and this issue will become history.
My issue was that I was unable to explain why this grounding needed
to be done, or to suggest other possible solutions, due to not
knowing the wording or the source of the requirement. It is sort of
an unusual situation.
Cheers,
Drake
At 04:47 PM 1/7/2009, you wrote:
>Hi Drake,
>
>Thanks for your detailed reply. Hmmm. Grounding / bonding ....
>always the most
>misunderstood, confusing, controversial aspect of electrical work.
>
>Some thoughts:
>
>1) The NEC is a MINIMUM standard.
>2) The NEC sometimes has to play "catchup" in the case of developing
> technologies such as PV.
>3) PV module and array grounding methods and requirements have
> "evolved" over time and continue to do so.
>4) Certain proprietary module / wiring / racking systems may include
> "devices identified and listed to bond adjacent module frames".
>5) The NEC is all about safety for people and buildings, and not so
> concerned about lightning related damage to sensitive, expensive
> electronics such as inverters and charge controllers.
>6) I think John Wiles recommended the star washer / bolt /
> weather resistant lug combination as a solution in the absence of a
> module manufacture's specific instructions.
>7) Response to your Question #1: I don't believe you will find this
> anywhere in the code. UL tests modules for "Bonding Path Resistance",
> ( http://www.ul.com/dge/photovoltaics/tests.html ), presumably using
> the designated frame bonding location and methods specified by the
> manufacturer. The details of this procedure and all of the
> listing process
> are available for a fee from UL. I'm told, (by a former NH
> State Electrical
> Inspector) you may be able to find this information, free of charge,
> at a good library.
>8) Response to your Question #2: See #6 above.
> Also, paraphrasing, the code does require that the
> removal of any module not compromise the bonding of
> any adjacent module.
>9) The much higher voltages and greater investments in today's systems
> make good grounding / bonding more important than ever.
>
>Thank you for bringing this to my attention.
>
>Dick
>
>Dick Ratico
>Solarwind Electric
>Bradford, VT
>
>
>--- You wrote:
>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 ---
>--- end of quote ---
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Drake Chamberlin
Athens Electric
OH License 44810
CO License 3773
740-448-7328
740-856-9648
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