grounding plate vs. rod? [RE-wrenches]

Scott Russell scottr at lotusenergy.com
Wed Dec 18 21:51:25 PST 2002


Thanks, all. 

No, I've never tested the soil composition here (or anywhere). We work
across a wide geographic and topographic range so it may be tough to make
generalizations about soil composition in Nepal. 

Convention is to put the coal directly against the copper plate (above and
below) and the connection point is simply nut/bolt/washers at three seperate
points across the plate face.

The truth be told, these guys would never let me dig a hole. They'd claim
it's because it's not work befitting of me, but they probably just think I'm
not up to it. :-)

More than anything, I just wanted to make sure that this plate approach
wasn't rooted in some old mythology that had been disproven long ago. Sounds
like my skepticism is clearly unwarranted.

Best,

Scott



-----Original Message-----
From: Matt Lafferty [mailto:pvpro at attbi.com]
Sent: Wednesday, December 18, 2002 7:54 PM



Wrenches:

Scott Russell wrote:

> I'm installing PV in Nepal for a Kathmandu-based company. They typically
use
> copper grounding plates (18"x18") here rather than the grounding rods I'm
> familiar with back in the good ol' USA. Our Nepali techs claim that the
> local soil composition necessitates taking extra steps to increase its
> conductivity. That is, using the larger surface area of a plate as opposed
> to a rod and burying it parallel to the surface, two or more meters deep
> sandwiched between two layers each of salt and coal. Does this sound
> reasonable/plausible?

Yes, this is plausible.  In fact, there are quite a few areas here in the
States that the conductivity of the soil isn't as good as it should
be....Almost nobody takes that into consideration.  At least the local
Nepalis have discovered this and have an answer for you.

As we've all heard many times, a lot of guys just drive a ground rod and
tell stories about how hard it was or how "you cut off the pointy end by a
couple of feet before you start driving it so the Inspector can see the
writing at the top end".  A 10' x 3/4" ground rod only has about 120 sq. in.
of surface contact, by the way.

Plate or "made electrodes" are a suitable and effective way to provide
grounding.  The NEC Handbook has some pretty good explanations and drawings
that can assist you.

A couple of questions:

1.  Which is directly against the copper, salt or coal?  (Bill B...salt,
copper, moisture absent air???)

2.  How are you connecting your electrode conductor to the plate?
(Exothermic, Direct Burial Mechanical Lug, etc.)

On the brighter side:  At least they probably don't have Prevailing Wage
Requirements in Nepal!  Perhaps tapping into the local labor pool is an
option?  Hope it's not in the mountains!  Besides, a little honest work
shouldn't hurt you.... ;-)

-Matt Lafferty
pvpro at attbi.com

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