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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