Module grounding revisited [RE-wrenches]

[Brad Bassett]

The trick is get electrical contact between the module frame and the 
rack. Many modules frames are so well anodized that electrical contact 
can't be counted on by just bolting them together. There must be a way 
to break through the anodized coating to get contact.

One method used by some is to put a star washer (stainless of course) 
between the module frame and rack where it is bolted down. Whether this 
gives adequate conductance or not I'm not sure. I also wonder how it 
will do over a period of years. It also wouldn't work with a clamp down 
type rack.

Another corollary issue is how to get a good, long lasting ground on any 
aluminum rack or module. Somewhere there is likely to be a problem with 
corrosion between the aluminum frame and the copper grounding wire. 
Inserting something stainless between might slow it down some. The best 
I've seen is a copper lug (GBL-4DB from Ilsco) held with a stainless 
bolt with a stainless washer between it and the aluminum frame (with 
copper ground wire of course).

I have a question about the size of the ground wire. I think I've read 
in the NEC that AWG #6 stranded or #8 solid is required where subject to 
physical damage. Does ground wiring in an array qualify as subject to 
physical damage (if the combiner is adjacent)? Or is #10 ground wire 
adequate? Since #10 or smaller interconnect wire seems to be accepted, 
maybe that's all that's needed for ground wire. Any thoughts?

Thanks
Brad Bassett

William Miller wrote:
One concept I had been wanting to research is that of grounding
> only the rack frame.  The Code seems to allow this:
> 
> 	(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. 
> 


Brad Bassett
bsbassett at earthlink.net

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