grounding array ? [RE-wrenches]

[Ray Walters]

At 12:08 PM 1/14/02 -0700, you wrote:
>>My opinion is to float the array. ...   ....   ...
>>There are many more benefits, but this would turn into long
>>dissertation.
>>
>>Regards.
>>____________________________________________
>>Kent Sheldon
>>Manager, Industrial Power Systems
>>SMA America
>
>
>Thanks, Kent!
>
>Any other agreement out there?
>
>Is anybody urging NEC writers to change the rule?
>
>Windy
>
Hi Folks;

First I'd love that dissertation Kent. 
Next a quote from " Lightning Protection and Grounding Solutions for
Communication Sites" published by Polyphasor :
 "Some manufacturers ground the negative side of DC operated equipment to
the chassis. This reinforces the need for local DC over voltage protection
since the chassis ground potential follows the rest of the ground system's
potential during a lightning strike and could go up."
  I can't quite figure their stance on grounding the neg. conductor. While
the above quote seems to advocate floating, an inspection of their
Polyphasor DC lightning protectors shows that they actually route negative
current through the unit's chassis.
Sorry to muddy the waters on this question, but I have struggled with it
for years. Sometimes I ground neg. sometimes I don't. It depends on how
good a ground I have (I usually ground neg. if I have a steel cased well)
and what the nominal voltage is (I almost always ground 48 volt, 12 volt
almost always floats).

All of the systems I've worked on that suffered signifigant lightning
damage had three things in common:
 
1. Neg. was grounded.
2. The ground was questionable but still to "code". (5/8" ground rods in
dry, rocky soil).
3. Delta lightning arrestors were installed.

Windy, I'm not currently lobbying the NEC, but I find lightning protection
to be the most dangerous issue I deal with, and the least addressed by the
NEC. While I have never seen an actual incident where a DC GFI would have
been useful, I have almost lost a customer to line surge from a nearby
strike. (It arced past and ruined a QO breaker, while a class t fuse and
Delta LA did nothing.) 
If one of my floating systems ever takes a hit I'll let you know.

Ray

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