Fw: Fw: Grounded for two weeks...hopefully longer [RE-wrenches]

Mon Apr 5 15:23:00 PDT 2004

===========================================================
INSTANT CAR INSURANCE QUOTE! Save time, save money, and 
get the best deal. Get quote, buy, and print insurance 
cards online!
http://click.topica.com/caab599bz8Qcsbz9JC9a/ Insurance4usa.com
===========================================================

Fellow Wrenches,
John Wiles' grounding piece.
Allan

Grounding PV Modules

Grounding PV modules to reduce or eliminate shock and fire hazards is
necessary but difficult. We use copper conductors for electrical connections
and the module frames are aluminum. As many of you know, copper and aluminum
don't mix as was discovered in numerous fires in houses wired with aluminum
wiring in the 1970's. PV modules generally have aluminum frames. Many have
mill finish, some are clear coated, and some are anodized for color. The
mill finish aluminum and any aluminum surface that is scratched quickly
oxidizes. This oxidation and any clear coat or anodizing form an insulating
surface that makes for difficult long-lasting, low resistance electrical
connections (e.g. frame grounding). The oxidation is not a good enough
insulator to prevent electrical shocks, but it is good enough to make good
electrical connections difficult.

Underwriters Laboratories (UL) who tests and lists all PV modules sold in
the US requires very stringent mechanical connections between the various
pieces of the module frame to ensure that these frame pieces remain
mechanically and electrically connected over the life of the module. These
low-resistance connections are required because a failure of the insulating
materials in the module could allow the frame to become energized at up to
600 volts (depending on the system design). The NEC requires that any
exposed metal surface be grounded if it could be energized. The installer of
a PV system is required to ground each module frame. The code and UL
Standard 1703 require that the module frame be grounded at the point where a
designated grounding provision has been made. The connection must be made
with the hardware provided using the instructions supplied by the module
manufacturer.

The designated point marked on the module must be used since this is the
only point tested and evaluated by UL for use as a long-term grounding
point. UL has established that using other points such as the module
structural mounting holes coupled with typical field installation
"techniques" do not result in low-resistance, durable connections to
aluminum module frames. If each and every possible combination of nut, bolt,
lock washer and star washer could be evaluated for electrical properties and
installation torque requirements AND the installers would all use these
components and install them according to the torque requirements (we all
have and use torque wrenches and torque screw drivers don't we?), it might
be possible to use the structural mounting holes for grounding.

Most US PV module manufacturers are providing acceptable grounding hardware
and instructions. Japanese module manufactures are frequently providing
less-than-adequate hardware and unclear instructions. Future revisions of UL
1703 should address these issues. BP Solar is to be congratulated for
getting their module listing to include making new grounding points at other
locations than the marked points.

In the meantime, installers have to struggle with the existing hardware and
instructions, even when they are poor. SWTDI has identified suitable
grounding hardware and provides that information when installers ask about
grounding-a frequent topic. And yes, we are using the hardware and methods
described below to ground Sharp modules in our new inverter test facility.

For those modules that have been supplied with inadequate or unusable
hardware or no hardware at all, here is a way to meet the intent of the code
and UL Standard 1703.

A thread-forming stainless steel 10-32 screw is used to attach an ILSCO GB4
DBT lug to the module frame at or adjacent to the point marked for
grounding. A #19 drill is required to make the proper size hole for the
10-32 screw. The 10-32 screw is required so that at least 2 -1/2 threads are
cut into the aluminum (a general UL requirement for connections of this
kind). The thread-forming screw is required so that an airtight, oxygen-free
mating is assured between the screw and the frame to prevent the aluminum fr
om reoxidizing. It is not acceptable to use the hex head green grounding
screws (even when they a have 10-32 threads) because they are not listed for
outdoor exposure and will corrode eventually. The same can be said for other
screws, lugs, and terminals that have not been listed for outdoor
applications. Hex-head stainless steel "tech" screws and sheet metal screws
do not have sufficiently fine threads to make the necessary low resistance,
mechanically durable connection. The only thread-forming, 10-32 stainless
steel screws that have been identified so far have Phillips heads; not the
fastest for installation.

The ILSCO GB4 DBT lug is a lay-in lug with a stainless steel screw made of
solid copper and then tin plated. It accepts a 4-14 AWG copper conductor. It
is listed for direct burial use (DB) and outdoor use and can be attached to
aluminum structures (the tin plate). The much cheaper ILSCO GBL4 lug looks
identical, but is tin plated aluminum, has a plated screw and is not listed
for outdoor use. We have not been able to identify an alternative to the
GBL4 DBT, but continue to search.

Yes, we would all like to use the module mounting structure for grounding. I
have encouraged UNIRAC and others to get their products listed as
field-installable grounding devices, but I suspect that they are running up
against that aluminum oxidation problem also as well as the lack of
consistency in tightening nuts and bolts in the field.

The code allows metal structures to be used for grounding and even allows
the paint or other covering to be scraped away to ensure a good electrical
contact. We see numerous types of electrical equipment grounded with sheet
metal screws and star washers. This works on common metals like steel, but
not on aluminum.

I am also trying to interest the module manufacturers in making that
aluminum connection in the factory and giving us a copper-compatible
terminal in the j-box or on the frame as is done with the 300-watt
RWE-Schott modules.

Unfortunately many PV systems are being grounded improperly even when the
proper hardware has been supplied. The picture below taken in March 2004
shows that even the proper hardware can be misused. Here, the
stainless-steel isolation washer has been installed in the wrong sequence
and the copper grounding wire is being pushed against the aluminum frame; a
condition sure to cause corrosion and loss of electrical contact in the
future.

4/2/04 John Wiles SWTDI/NMSU jwiles at nmsu.edu

> Allan:
> Feel free to post the attached.  I'll use it in an article sometime.
> >John, this is good; care to comment?
> >Allan
> >
> >----- Original Message -----
> >From: "Geoff Greenfield" <Geoff at Third-Sun.Com>
> >Sent: Thursday, April 01, 2004 8:40 AM
> >
> >I agree that this is an area of big potential improvement...
> >
> >We currently use stranded bare #10 with crimp lugs and "green" screws to
> >bond all panel frames, rack and poles, with #6 solid and tinned
mechanical
> >lugs where we are "subject to abuse"...  My personal array has 7 years
with
> >the crimp lugs starting to rust but still good mechanical and electrical
> >connection.  Probably not going to last 30 years!
> >
> >I like the zig zag through SS screws approach that was posted- especially
> >for flush mount roof jobs - will be trying it!
> >
> >Here is my question? - On the concept of using racking AS grounding (with
> >star washer for positive connection) I have heard of large arrays doing
this
> >and passing inspection.  Specifically - BP supplied and installed a 25KW
> >ground mounted affair that used galvanized steel racks made out of tube
> >steel posts and a primary E-W strong back, then with unistruts attached
to
> >that and panels attached to that.  No grounding other than the "steel"
> >racking.
> >
> >Now, congregation, please open the good book and turn with me to the
> >grounding 250:verse 136...
> >
> >And the NEC said ye shall ground the panels... and it was good....
> >
> >
> >Ok... seriously:
> >
> >Looking at NEC 250.136 we see exception A for "non-current carrying metal
> >parts" - "...secured to or in electrical contact with a metal rack or
> >structure provided for its support and grounded by one of the means in
> >250.134.  (metal frame of a building doesn't count for AC equipment)"
> >
> >250.134 then discusses conductors or methods, referencing 250.118.
> >
> >250.118 is types of grounding conductors - listing wire, but also
includes
> >cable trays and gutters listed for grounding (referencing 392.3C and
397.7)
> >
> >I am assuming that unistrut and other struts are listed as grounding
> >conductors and this is how this system passed.  Perhaps in addition to
> >asking the PV manufacturers to broaden their grounding methods, we should
> >approach UniRac and the rest and get their products listed as grounding
> >conductors.  I would rather string a #6 along a large array bolting to
every
> >second unirac rail, or even the steel substructure!  Am I correct that
our
> >answer is already in the Code and we just need to come up with a way to
> >comply? (like switch to unistruts until the racking companies get with
the
> >program?
> >
> >Perhaps some comments from Pastor Wiles...?
> >
> >Sincerely,
> >
> >Geoff Greenfield
> >NABCEP Certified Solar PV Installer TM
> >

===========================================================
Let University of Phoenix make 2004 your year. Evening, 
weekend or FlexNet® classes – over 130 locations. Look 
into our programs and get the degree that gets you going!
http://click.topica.com/caab6aBbz8Qcsbz9JC9f/ UOP
===========================================================

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://lists.topica.com/lists/RE-wrenches/read

List rules & etiquette: www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

For Topica's complete suite of email marketing solutions visit:
http://www.topica.com/?p=TEXFOOTER
--^----------------------------------------------------------------