DC-GFP/2 protection [RE-wrenches]

[Ray Walters]

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.

Ray



 At 09:42 PM 8/22/02 -0400, you wrote:
>Jeff,
>
>Wow! What a timely message for me to see. I have always gone by the book and
>bonded DC negative to ground at one point in the system and have experienced
>no more than the occasional lightning issues.
>
>However I have been recently considering a change to a floating DC system. A
>tech at one of my distributors had my ear on this issue and he was convinced
>that floating the DC negative would help with lightning protection. He also
>said that there was some sort of movement to do away with the language in
>the code that mandates the DC negative bond to ground.
>
>Dave Palumbo
>IP&L
>
>
>-----Original Message-----
>From: Jeff Yago [mailto:jryago at earthlink.net]
>Sent: Thursday, August 22, 2002 9:12 PM
>To: RE-wrenches at topica.com
>Subject: RE: DC-GFP/2 protection [RE-wrenches]
>
>
>We just returned from inspecting a brand new 4 month old system (that we did
>not install!!) that had BOTH SW5548 Trace inverters "fried" by lightning.
>This was a 4800 watt totally off grid system.  The AC side of the inverters
>supply a standard 120/240 volt house panel that was grounded properly.  The
>ground mounted array frame was grounded properly also.  However, the
>negative of the DC side of the inverter, batteries, and charge controllers
>were not grounded.
>
>The lightning was "nearby" but was not a direct strike.  Since there was no
>grid connection, the surge could not have entered the AC side.  I for one
>like grounding the DC side and wish this installer had done so also.
>
>Jeff Yago
>
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