DC-GFP/2 protection [RE-wrenches]

[Joel Davidson]

All good points, but it is not expensive and is worth the time to measure
resistance (<5 ohms) between equipment and the earth.


Ray Walters wrote:

> Hi Guys;
>
> Well I fried a pair of SW4048s and we DID ground negative. Jeff, when you
> say that the PV frame and AC were properly grounded, what testing did you
> do to determine that? What was the resistance or (more importantly for
> lightning protection) what was the impedance to ground? What are the soil
> conditions at the site? To say it was properly grounded, you really need to
> answer those questions or you need to tie to a steel cased well.  When the
> ground is questionable, I now advocate floating DC negative.
>
> Here's the choices:
>
> 1.Expensive ground testing and certification.
> 2 Bond to a steel well casing.
> 3.Sink two rods and consider floating the DC negative and adding extra
> protection.
>
> Even if you do everything by the book or beyond, you may someday have an
> installation damaged.  Check out Polypasher, they protect communications
> towers that take so many direct hits,they install "Event" counters. I'm not
> hawking their wares, (that previously mentioned system had some of their
> stuff and Delta  LAs) but they really have studied this stuff in depth.

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