Gridtie, breaking grounded conductor [RE-wrenches]

[Robert Warren]

If the PV system was one with amorphous modules instead of crystaline, 
that capacitive charge that John B. and Bill Brooks speak of is not such 
a small shock: it can pack quite a wallop! Apparently the nature of 
amorphous cells is conducive to building up and holding a huge capactive 
charge. Sure, it will zero out through your DVM, but it it happens to 
zero out through your fingers, it can knock you on your butt, as friend 
or mine in Scotland found out while testing a 12 kW Unisolar amorphous 
system while standing on a metal roof.
 The lesson here is to always treat all wires as live. I don't think 
this means that we need a disconnect on the roof, though. 
 As for the location of the connection of the negative to ground (or the 
suggestion that it be possible to break it), doesn't the recommended 
practice of a UL listed device such as the Sunnyboy inverters 
automatically supercede any new and fuzzy installation concept that 
inspectors might come up with? I remember a clause in the NEC code 
saying something to the effect that the manufacturer recommendations may 
superceed the NEC code in terms of being more safe than Code. Let the 
GFI do its job.
Robert Warren 


John Berdner wrote:
>   
> The shock the inspector experienced form the negative conductor is a
> capacitive discharge due to the small capacitive coupling between the
> array and earth (as Bill Brooks correctly pointed out).  
> You can verify this with a DVM measurement from PV + to ground and PV -
> to ground with the GFDI fuse removed.
> Unless you have a ground fault the system is ungrounded at that point
> and you should see about 0.5 * Voc on each measurement.
> This voltage should decline towards zero as the capacitive coupling is 
> discharged through the DVM.
> A fixed voltage that does not decline normally indicates a ground
> fault.
> 



Check out my website on making your own fuel: 
http://running_on_alcohol.tripod.com 
robertwarren at mail.com

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