Module grounding analysis-600V residential [RE-wrenches]

Brian Wiley btw at we-llc.com
Wed May 23 06:32:43 PDT 2007


Brian Wiley of Wiley Electronics LLC:

I think the question of how to safely remove a module with a short 
circuit is very simple.  Install a temporary equipment ground to the 
module with enough wire length to allow handling.

Some people have intimated that this is a problem with the use of the 
new ground clips, but I believe this is also a problem with the more 
common method of attaching lay-in lugs with a thread forming screw (and 
indeed any grounding which can not be directly inspected).  In my 
testing I have found them to be an unreliable method which is prone to 
corrosion.  So I would not bet my life on them to provide a ground after 
some years exposed to the elements.  There are a lot of such systems 
installed, so this problem will be around for many years.

We should also examine industry practice in servicing.  In the AC world 
one first turns off the power.  This should also be the practice for 
solar.  There is no good reason that modules cannot be covered before 
servicing.  For large installations, a subsection of the array can be 
isolated at the combiner box then the subsection in question covered.  
No power from the modules, no potential for shock, no matter what the 
wiring problems.

I think that the Europeans actually have a much safer system than ours 
because their systems are "ungrounded".  In your scenario of the 
ill-fated Frisbee girl, if she were European, there would have to be two 
exposed conductors lurking and she would have to contact them both.  
Pretty unlikely compared to her American counterpart, where we 
intentionally ground the return conductor and make it much easier for 
the poor girl to meet her demise.

Brian Wiley
---------------------------------------------
Wiley Electronics LLC
1131 Kings Highway
Saugerties, NY 12477

voice:    845.247.2875 ext. 1#
fax:      845.246.0189
website:  http://www.we-llc.com
---------------------------------------------


William Miller wrote:
> 
> I am resending the post below because Topica apparently ate my first 
> attempt:
> 
> 
> 
> Friends:
> 
> I read the article, suggested on this forum, analyzing grounding 
> problems.  The article was written by Thomas Bowes.  Here is a more 
> manageable link to the article:
> 
> http://tinyurl.com/yo3ckx
> 
> I found the article to be very germane to safety issues emerging as 
> industry installation practices evolve.  The most important point made, 
> in 
> my opinion, is the point that installation of 600 volt systems in 
> residential settings is a very new concept.  This idea has implications 
> beyond just the grounding issues.
> 
> I have some very strong safety concerns prompted by this knowledge.  
> What 
> causes me dismay is that the industry is hell-bent on cheapening and 
> speeding up installation techniques.  I believe the motivation is partly 
> to 
> make Utility-interconnected PV systems more accessible to the masses, 
> which 
> is a good motivation.  The other motivation is to obtain an advantage 
> over 
> competing vendors of systems, a bad thing.
> 
> It is, in my opinion, not a matter of if, but when we kill our first 
> human 
> (if it has no happened already) with our shoddy installation 
> procedures.  My scariest scenario is of the child who throws a Frisbee 
> or 
> ball onto a roof to have it become stuck under a PV array.  A USE cable 
> has 
> been rubbing against abrasive roofing material, exposing the 
> conductor.  The child finds a length of metallic pipe in the garage and 
> uses it to dislodge the toy.  You imagine the rest of the story...
> 
> The trend in reducing wire protection is driven also in part by 
> practices 
> in Europe.  It is my understanding that the "quick-connect" is 
> ubiquitous 
> there and that leads from the roof to the inverter and from the inverter 
> to 
> the AC distribution are all USE or similar cable, not protected by 
> conduit.  Does anyone have experience with these European standards or 
> practices?
> 
> Lastly, the point made in the article is very correct in that if a 
> module 
> in a "top-down" installation has a short circuit, how does one remove 
> the 
> module without getting electrocuted?  This is particularly risky when 
> one 
> can not verify the short circuited module until one removes it from the 
> ground connection and undergoes a very real risk of becoming the ground 
> path, with possible fatal consequences.
> 
> I'd like to hear from those that share my concerns about these 
> practices.  I would hope we could, as a group, put aside our pursuit of 
> paying contracts long enough to convene an installer based group to 
> examine 
> some of these concerns.
> 
> 
> William Miller
> 


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