[RE-wrenches] To Megger or not to Megger

Fri Jan 8 13:41:47 PST 2010

Hi Bill,

I wanted to follow up on your results finding a ground fault with a lower resolution megger. 

Do you think the .1MOhm meters will work in field applications? 

Do you know of any .001MOhm meters like the old 1520?

I have taken a  position with a cadtel mfgr as their field application engineer.  I hope to be using your consulting services if I get over my head. 

Thanks and Happy New Year!

-Wes Kennedy

303-653-3073

--- On Tue, 4/28/09, Bill Brooks <billbrooks7 at yahoo.com> wrote:

From: Bill Brooks <billbrooks7 at yahoo.com>
Subject: Re: [RE-wrenches] To Megger or not to Megger
To: "'RE-wrenches'" <re-wrenches at lists.re-wrenches.org>
Date: Tuesday, April 28, 2009, 11:39 AM

Dave, 

The issue is definitely resolution. The cool thing about the
Fluke 1520 is that it goes down to 0.001MOhms (1000 Ohms). That is the
resolution you are looking for. Neither of the current Flukes go low enough.
That is why I’m going into the field later this week to see how a 0.1MOhm
meter stacks up to finding faults—I have an array with a pesky fault that
should make it fun. 

Many arrays will ring out as a faulted array when, in fact,
everything is fine. This is especially true of a-Si arrays with low quality
glass. They are very leaky. I’ll keep looking and report back on a
recommendation for Christmas shopping. 

Just to add punctuation to this thread, I always recommend that
contractors megger their arrays, because it has saved my butt several times.
Also, with exterior wiring systems it is even more important. The problem in
the early days is that people would whine about the $600-$1000 price tag. In my
opinion, that argument is gone. With contractors routinely putting down $1400
for a SunEye, the value of a good megger is similar and costs less. 

Bill. 

From:
re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of David
Palumbo

Sent: Tuesday, April 28, 2009 7:59 AM

To: gilligan06 at gmail.com; 'RE-wrenches'

Subject: Re: [RE-wrenches] To Megger or not to Megger 

Matt, 

“Muggering”, I think that will catch on. The last
post, I think, ol’ Uncle Bill Brooks (4/13/09 8:17 PM) had on this topic
raised a concern about “not having enough resolution in the low impedance
area. PV arrays can have an impedance to ground of a slow as 2kOhms. A
resolution of 0.1MOhms will likely not cut it.” Bill went on to say that
he had bought a cheaper meter to test out “for fun”.  Some of
us do enjoy “muggering around”. 

So my question is.  Do  the Fluke 1503’s and
1507’s have enough resolution in the low range?  

Dave 

From:
re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Matt
Lafferty

Sent: Tuesday, April 28, 2009 9:56 AM

To: 'RE-wrenches'

Subject: Re: [RE-wrenches] To Megger or not to Megger 

RE: Suggested replacements for Fluke 1520 and "pricey
meters"... Good News below! 

Another Wrench sent me a note off-list last night, asking how much
a "muggering" would cost. Here's what I sent him: 

When I got that 1520 it was just over $600. I just
checked online and find that it's a discontinued item... Bummer!  

Fluke recommends the 1587 or the 1507 or the 1503. They also
mention the 1577, but it's an ugly stepsister, or maybe a retarded adopted
relative, to the 1587.  

The 1587 is basically a multimeter that also has a <TEST> button to
discharge a high voltage shock into the sample under test... It runs about $620
from standard distributors. http://us.fluke.com/usen/products/Fluke+1587+1577.htm?catalog_name=FlukeUnitedStates  You
can get it for $522 here:  

http://www.testequipmentdepot.com/fluke/megohmmeters/1577_87.htm  NOTE: It
does not test at 10A in DMM mode which means it wouldn't be able to test
short-circuit current in strings. Don't bother with the 1577!  

The 1507 & 1503 are more robust equipment. You can check them
out here: http://us.fluke.com/usen/products/features.htm?cs_id=35391(FlukeProducts)&category=HMA(FlukeProducts) 
While they do measure AC & DC Voltages to 600V as well as some lower ohm
& continuity work, they are really more tailored to being a megger. The
1503 will suffice for most of what I expect you will get into, but there are
some features on the 1507 that might make it worth considering. Mind you, I
haven't looked at at price on either yet, so that last comment may just be
noises coming out my ass.  

The 1507 has a Compare function which basically sets up a Pass/Fail
value so you can quickly run through repeated tests. This would be useful for
doing larger systems where you are testing dozens or hundreds of circuits at a
time. For my purposes, I want my guys to think a little more than "Buzz =
OK" and I want them to write an actual tested value down on a piece of
paper so this is not a big plus to me. 

The 1507 also does Polarization Index and Absorption Ratios. These
are more advanced di-electric tests that you are not likely to need in smaller
scale PV. Use of these features would come into play when playing with real
high-voltage gear or transformers. Might also come into play on super-sensitive
equipment. They might also be used to assess older or aging underground or
overhead feeders.  

The 1507 & 1503 both have an Earth Bond Resistance function
which is likely to become more of an issue in the future. This feature lets you
test the resistance between a grounding electrode or a grounding electrode
conductor and actual earth. Another use for this feature would be to set the
output to 1kV, connect the alligator jaw to one of Mike Gripando's extremities
and use the probe lead as a tongue depressor while you push <TEST>. This
feature used to be in a single-purpose tester that ran >$2K. They also both
have backlit displays which comes in real handy out in the field. 

The primary features you want are: 500V & 1kV Test Voltage and
2 Gohms (2,000 Megaohms) or above for the top end of the range. Any of the 3
meet this spec.  

Well, I just checked prices for the 1503 & 1507 and I'm
pleasantly surprised. The 1503 ranges from about $291-$370.
Here's the place I found it for $291  http://www.testequipmentdepot.com/fluke/megohmmeters/1503.htm That's
marked down from the regular price of $342.   

The 1507 ranges from about $385 to $500. Here's where I found it
for $385... http://www.testequipmentdepot.com/fluke/megohmmeters/1507.htm  That's
a special price, for you only, down from $454.  

All things considered if I were in your shoes, I'd go for the 1503.
That give you a solid megger that you can dedicate to that purpose for a
reasonale muggering. If it were me, in Matt's shoes... Oh, what am I saying?
I've already got mine and I just found out I paid too much for it! But I have
Battery Check... Neener neener neener! 

Be safe out there! 

Matt Lafferty 

I hope more hands go up on this topic. Thanks for asking, Keith. 

Peace and Palm Trees everybody, 

Matt Lafferty 

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