Where is Ground Clamps [RE-wrenches]

[Bill Brooks]

Bob-O,

Don't be so quick to discount internal shorts. I just saw one on a 20 kW
array a few weeks ago. It caused the module glass to shatter. Energized
frames used to be more common with modules back in the 1980's in high
voltage systems. Still can happen though. Now that we have USE-2 cable
running all over the place it is much more likely. How about the wires
rubbing on the roof surface when not supported properly--happens all the
time. Now you have a conductor with the jacket abraded and little Jimmy
grabs it and the frames at the same time--bummer dude.

Having a connection of a current carrying conductor to a module frame is
always a hazard whether the frame is grounded or ungrounded. It is actually
more of a hazard to NOT ground the frames because a potential difference
exists between the frame and ground so little Jimmy becomes the conducting
path when he touches anything grounded (conduit) and then you have to make
funeral arrangements and it's a big bother. Effectively grounding the module
frames allows your ground fault detection circuit to kick in and detect the
problem before it becomes a fire hazard and hopefully before the ground
connection degrades to high resistance.

Bill.




-----Original Message-----
From: Bob-O Schultze, Electron Connection
[mailto:econnect at snowcrest.net]
Sent: Monday, April 21, 2003 3:13 PM
To: RE-wrenches at topica.com
Subject: RE: Where is Ground Clamps [RE-wrenches]


Bill,
I certainly agree that an ungrounded energized module frame could be
bad news. Have you EVER seen one? Has anyone else? It seems to me
that the likelihood of an internal short causing that to happen is
almost nonexistent. True, a connecting conductor could rub the
insulation off and short to a frame (another reason to use flexible
nonmetallic conduit instead of MC cables) but that makes the same
case for NOT grounding the module frames.
Best, bob-O

>I believe that we need racking systems that provide for effective grounding
>of all the modules. This is a very real safety issue. An energized module
>frame without effective grounding is a huge hazard.
>
>Bill.

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