Where is Ground Clamps [RE-wrenches]

[John Berdner]

Jay:

The problem with grounding through the frame is that many of the frames
are anodized aluminum (read as excellent insulator).  Unless the
structure has been evaluated as a grounding member you can't rely on it
to provide the equipment ground.  I think this could be solved with
insulation piercing hardware, e.g. star washers, but so far none of the
structure manufacturers has developed this concept to the point that it
can be listed as a means of grounding.  In absence of Listed "systems"
that provide equivalent grounding means, the Code says you have to run a
ground wire to every module to make sure it stays grounded.  The UL
requirement for a ground is 0.1 Ohms at 60 Hz.  Given that we are
talking about dc I think UL would also want to see a dc impedance
measurement as well.  

Based on my own experience I have measured grounding impedances far
above this level when using only the frames for grounding.  Others such
as J. Wiles and B. Brooks have also confirmed high ground impedance on
frames when only the structures are used. Until we have a grounding
structure system I think you have to run a ground wire (even one long
one daisy chanied) to every module.  Also, J. Wiles has convinced me
that all splices in the equipment ground wires should made with "non
removable" pressure connections, i.e. butt splices or ferrules. Just my
$0.02.

If you have any questions or if I may be of any further assistance,
please do not hesitate to contact me.

Best Regards,

John Berdner

SMA America, Inc.
12438-C Loma Rica Road
Grass Valley, CA  95945
530.273.4595 - Tel
530.274.7271 - Fax

-----Original Message-----
From: Jay Peltz, Peltz Power [mailto:jay at asis.com] 
Sent: Monday, April 21, 2003 09:50 AM
To: RE-wrenches at topica.com
Subject: Re: Where is Ground Clamps [RE-wrenches]

Hi Dean,

Can you give me the code # that states all panels must be grounded in
addition to the metal frame they are on?

One installer I know puts in the permit all grounding to be done in
accordance with 250.136(a).  This allows for only a single ground wire
from
each seperate array.  Makes it much easier.

thanks,

jay

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