600 vdc arc testing [RE-wrenches]

[Bill Brooks]

Joel and Graham,

USE cable has a poison impregnated in it that keeps rodents away. It is used
on literally millions of homes in the U.S. and is exposed to squirrels (they
like to use it to get from one place to another) and other varmints. This
type of cable has not had the problems that other cables (TV, etc...) can
have. I'm sure there may be exceptions, but there are probably dead animals
to prove it too.

Bill.


-----Original Message-----
From: Joel Davidson [mailto:joeldavidson at earthlink.net]
Sent: Tuesday, January 22, 2002 4:32 PM
To: RE-wrenches at topica.com
Subject: Re: 600 vdc arc testing [RE-wrenches]


We installed a couple hundred 4 and 6 kW Omnion inverters for
residential and commercial systems in Sacramento back in 1995 and only
had one 600 volt arc when an installer accidentally shorted the bi-polar
300 VDC in the combiner box with a screwdriver. Since then, high voltage
c-boxes are larger with more space between the terminals and more room
to work.

In 35 years, we never had squirrels, mice or rats eat wire insulation.
When I investigate "rat eats insulation" stories, they end up to be
hearsay that can not be corroborated with two or more witnesses. I've
worked in and inspected over five thousand homes in the U.S. and other
countries and have seen only one case of wire eaten by rats. In rural
Arkansas 25 years ago, the lady of the house gave fried chicken lunch to
the men working on her house. The men returned to work without washing
their hands. The rat ate the fried chicken flavored insulation and got
fried himself.

If you panelize in your shop, you have better quality control and better
utilization of shop and field time.

If PV module manufacturers make bigger and bigger modules, field wiring
will someday only require two connections - and a skyhook. PV modules
can be too big, but you can't tell that to guys who feel the need to
prove that their thing is bigger (and therefore better?) than the other
guy's thing. Over-sized modules often require special shipping, handling
and cranes that increase overhead and labor costs.

graham at solarexpert.com wrote:
>
> Hi Christopher,
>
> Thanks for taking the time to test the arc length of 600 Volts DC as
> well as making it available on your web site.  The potential for arcing
> on my customers residential roof tops scares me.  There are quite a few
> 600 volt systems being installed in southern California at this time,
> and almost all of these installations are using quick-connects between
> the modules.  I have even heard of an individual installer that pulls
> apart a quick connect to pull an arc to light his cigarette. 600 volts
> systems with quick-connects are fast an easy to install but are they
> truly safe for residential applications?
>
> I have had problems at my house with squirrels gnawing on telephone,
> cable TV as well as power lines.  Last year a squirrel chewed through
> the line drop across my back yard and burning insulation was dripping
> onto the lawn.  The Burbank Department of Water and Power came out and
> found the dead squirrel and mentioned that this is a common occurrence.
> This has kept me from installing high voltage systems with quick
> connects.
>
> Would it be safer if the USE cable is armored and a clamping devise or
> cover eliminates the chance of the connections pulling apart?
>
> I would really appreciate advice from members of the wrenches list who
> have been working with PV for a much longer time than the guys
> installing systems locally who keep advising me that I am crazy
> panelizing modules with conduit in the shop.
>
> Graham Owen
> GO Solar Company
>
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