Module grounding revisited [RE-wrenches]

[Nick Nicholas]

Hi William:
    It is my understanding that a rack must have a UL listing which
specifies that modules connected to the rack are considered to be
"electrically connected" to the rack.  It is my understanding that most
racks, including Unirac, have not been rated for this application.
    What I find most excessive is to ground an array that is located on
steel poles buried in the  ground with multiple yards of concrete
surrounding the steel pipes.  Why ground any of it?
    Nick

Alternative Power Systems
www.alternativepowersystems.com
aps at sbcglobal.net
135 Colfax Ave.
Grass Valley, CA 95945
(530) 274-0588 phone
(530) 274-0589 fax
----- Original Message -----
From: "William Miller" <wrmiller at slonet.org>
To: <RE-wrenches at topica.com>
Sent: Tuesday, October 29, 2002 2:04 PM
Subject: Module grounding revisited [RE-wrenches]


Friends:

I am researching some new module mounting for rooftops-- more on that later
as it develops.  One question pertinent to the design is module frame
grounding.  One concept I had been wanting to research is that of grounding
only the rack frame.  The Code seems to allow this:

690.43 Equipment Grounding.
Exposed non-current-carrying metal parts of module frames, equipment,
and conductor enclosures shall be grounded in
accordance with 250.134 or 250.136(A) regardless of voltage.

Researching further:

250.136 Equipment Considered Effectively Grounded.
Under the conditions specified in 250.136(A) and (B), the
non-current-carrying
metal parts of the equipment shall be considered effectively grounded.
(A) Equipment Secured to Grounded Metal Supports. Electrical equipment
secured to and in electrical contact with a metal rack or structure provided
for its support and grounded by one of the means indicated in 250.134.
The structural metal frame of a building shall not be used as the required
equipment grounding conductor for ac equipment.

Therefore, if one grounds a rack frame, the modules being "secured to and
in electrical contact with" the racks renders the module frames
"effectively grounded".

Comments?

William Miller


PS:  I am now using the CD version of the 2002 NEC.  It really makes this
research easier.


WM




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