[RE-wrenches] Module shorting to ground?

[Kelly Larson]

Hi Rebecca,

If you suspect the wires in conduit, you can megger just the wires by disconnecting all the wires on both ends of the conduit, wirenutting them off on one end, and meggering them on the other end.  Megger between two of the wires at a time, and repeat until all the wires have been tested against each other and each is tested against the metal conduit, (if any).  There should be very high resistance between all of them and between them and the metal conduit.

To megger an array:

Remove the array connection to the inverter!  Cap that end of the wires with wirenuts.
Remove any surge protection devices!
Be sure that you connect the positive of the megger to the negative of the array (this is important to get right)
Connect the negative of the megger to the grounding conductors
Make sure all the metal of the system is clear of people and animals.  (Don't touch any metal)
Energize megger.  Use the 50V setting, (if the megger has that low a setting), it will show something if there is a problem that you are picking up with a multimeter
	or use the lowest setting.  Don't use more than 500V.

I am not sure the megger is the right tool to diagnose a module and prove it has an internal GF to a module manufacturer.  Some module manufacturers say not to megger their modules.  

Hope that helps.  Let us know!

Blessings,
Kelly


On Oct 27, 2012, at 7:25 AM, Rebecca Lundberg wrote:

> I have an array that has been up and running with no problems for 6
> months. The array includes 58 Sanyo HIT 220 watt N-Series modules, 13
> of which are on Enphase M210 and the rest in strings to (2) Power One
> transformerless (ungrounded) inverters. This week one of the Power One
> inverters shows a RISO error, indicating a connection to ground on one
> of the current carrying conductors.
> 
> I went out yesterday to look at the array, thinking these were the
> three potential issues (in descending order of likelihood):
> - animal damage to the wires (though there are no trees near the house at all)
> - contractor damage to wires (no work has been done on roof or attic
> since we were there)
> - inverter problem
> 
> I found one inverter input that shows continuity to ground at the DC
> disconnect (which indicates the inverter is doing just what it is
> designed to do!). I opened the Soladeck on the roof (which is where
> the PV output circuit/PV wire is transitioned to wire in conduit run
> through the house), disconnected the connection, and found the PV
> output circuit itself shows continuity to ground. I inspected the
> array carefully, and all wires are strapped securely off of the roof
> and out of sight, everything looks just as I left it 6 months ago.
> I've dealt with significant animal damage before and know what to look
> for.
> 
> My question: I can lift each of these 8 modules in the string up and
> check the wires carefully, but outside of that being a hidden cause,
> is it possible that one of the modules itself is shorting to ground?
> If so, how do I check that and what else will I need to do to prove
> that to the distributor for warranty replacement? So far I've used the
> continuity tone on the volt-meter for testing the short to ground. I
> have a megger but it is new, so, therefore, is my knowledge of how to
> use it...
> 
> Thanks in advance.
> 
> Keep Shining!
> Rebecca Lundberg
> NABCEP Certified Solar PV Installer ®
> Owner/CEO, Powerfully Green
> Rebecca.Lundberg at PowerfullyGreen.com
> 763-438-1976
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