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#81981 - 10/10/02 07:46 AM resistance on groung rod
Reel-Break Offline
Member
Registered: 04/04/02
Posts: 178
Loc: nc
Is it possible to measure the groung rod resistance with a normal meter say fluke 87 or 175? If so how do you take the measurement.
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#81982 - 10/10/02 07:58 AM Re: resistance on groung rod
sparky66wv Offline
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Registered: 11/17/00
Posts: 2232
Loc: West Virginia
The only way I've known of testing ground rods without a ground-testing meter, is to disconnect the EGC, place a 5A cartridge fuse in line with the EGC and a 120V line, turn on the power *briefly*, and if the fuse blows, you're done, if it don't, then drive another rod. Gives you a "threshold" of 24 Ohms, rather than the NEC 25, but it works. If you've got (closer to) 125V (we do here in Greenbrier County) then it's a perfect 25 Ohms.

Plus, you can gather nightcrawlers after the test!

I also read this in (I think) an older version of the American Electrician's Handbook (say, 1970's?)...

Kids, don't try this at home!
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#81983 - 10/10/02 09:07 AM Re: resistance on groung rod
txsparky Offline
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Registered: 05/25/01
Posts: 552
Loc: Magnolia,.Texas U.S.A.
I think I'll go gather some worms and find that fishing hole Joe took a picture of
Now where did I put that" 5amp worm gatherin tool "
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#81984 - 10/10/02 10:03 AM Re: resistance on groung rod
Bjarney Offline
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Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
'66wv—That’s a very interesting proposal. What would be considered a proper waiting period for fuse operation? Any difference for time-delay type versus less-expensive one time?
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#81985 - 10/10/02 05:33 PM Re: resistance on groung rod
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6776
Loc: Brick, NJ USA
Reel-Break:
Most contractors in our area just drive 2 rods from the get-go. Most AHJ's require documentation of the 25 ohms or less, and a meter to test and print results is pricey. Rods are cheap, and driving them with a roto hammer is quick.

66 thats a test to remember, I'll pass it on to my guys. Do you need "documentation" for your AHJ's or???

John
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#81986 - 10/10/02 05:54 PM Re: resistance on groung rod
sparky66wv Offline
Member
Registered: 11/17/00
Posts: 2232
Loc: West Virginia
Hee hee...

I've never tried this method, just read about it once and found it to be intriguing!

PoCo wants two rods here, period. No fun!



To further ReelBreak's Q, what minumum voltage and sensitivity must a meter operate at to be useful for ground rod resistance testing?

My DMM (Fluke T-5 1000) will easily meter 25 Ohms, why won't it work on rods?



[This message has been edited by sparky66wv (edited 10-10-2002).]
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#81987 - 10/11/02 04:04 PM Re: resistance on groung rod
watthead Offline
Member
Registered: 10/13/01
Posts: 172
Loc: South Carolina
66
the reason we can't use our flukes to do this is because we don't know exactly where to stick the other probe into the earth. this is why biddle can get a grand for these instructions supplied with their meters.
watt
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#81988 - 10/11/02 04:16 PM Re: resistance on groung rod
Roger Offline
Member
Registered: 05/18/02
Posts: 1716
Loc: N.C.
There is a very reasonably priced tester available in the store here.

As far as paying big bucks for instructions, save your money and go here, http://www.tradeport.on.ca/ApplicationNotes/aemc.pdf

This is almost identicle to Biddle's instructions, and a little more detailed.

Roger
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#81989 - 10/11/02 06:05 PM Re: resistance on groung rod
sparky66wv Offline
Member
Registered: 11/17/00
Posts: 2232
Loc: West Virginia
Could we check resistance from the opened EGC to the neutral? Wouldn't we be testing for continuiuty for any and all grounding electrodes attached to the grounded conductor?

How about to the nearest PoCo rod?

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#81990 - 10/11/02 06:27 PM Re: resistance on groung rod
Tom Baker Offline
Member
Registered: 10/09/01
Posts: 30
Loc: Bremerton WA
A ground resistance tester uses three electrodes, one is a reference electrode. A fluke DMM just won't work.
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