Module grounding revisited [RE-wrenches]

Joel Davidson joeldavidson at earthlink.net
Tue Nov 5 18:23:15 PST 2002


Bill's right, but use your ohmmeter anyway.

A good way to show your off-grid customers to why they should keep their
batteries clean is to set your voltmeter on 20VDC and put one lead on a battery
terminal and the other lead on the case to measure voltage. Then tell them to
neutralize the outside of the case with some Arm & Hammer. Sure, there's not
much current, but the "voltage leak" gets their attention.

Windy, I'm going to get that $50 clamp meter you mentioned next time I'm at
Sears.

Lately, I've been using a Test Products International (TPI) portable infrared
thermometer (model 371) that I bought at Fry's Electronics for under $100. Just
aim the laser and measure cell temperature. Pretty accurate.

Best regards,
Joel Davidson, incurable tool junkie.

Bill Brooks wrote:

> Joel,
>
> Remember that resistance readings without appreciable current flow will not
> be accurate. That is why ground resistance testers are so expensive.
>
> Bill.
>
> -----Original Message-----
> From: Joel Davidson [mailto:joeldavidson at earthlink.net]
> Sent: Tuesday, November 05, 2002 5:46 PM
> To: RE-wrenches at topica.com
> Subject: Re: Module grounding revisited [RE-wrenches]
>
> Thanks Ron. Sapphires for frames. No wonder PV is so expensive :-)
>
> It is worth taking a minute or two to pull out your multi-tester and measure
> solar module frame resistance. The anodized skin is non-conductive. The
> metal around the holes drilled in the frame are conductive. While you are at
> it, measure an installed array mount for less than 5 ohms to earth ground.
> The scientific method: observe, experiment, hypothesize.
>
> Ron Schroeder wrote:
>
> > Question:
> > ?Is anodizing a barrier to conductance?
> >
> > Answer:
> > Yes, absolutely.  Anodizing is aluminum oxide.  Aluminum oxide is
> > sapphire.  Sapphire is one of the best insulators known.  At my "day
> > job", we often use 2 anodized aluminum surfaces (with smooth edges)to
> > stand off several thousand volts.  You must brake thru the anodizing to
> > get conduction.
> >
> > Ron Schroeder
> > Brookhaven National Lab
> > Energy Efficiency Systems
> > Long Island NY
> >
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