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resistance on groung rod #81981
10/10/02 09:46 AM
10/10/02 09:46 AM
R
Reel-Break  Offline OP
Member
Joined: Apr 2002
Posts: 178
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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Re: resistance on groung rod #81982
10/10/02 09:58 AM
10/10/02 09:58 AM
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
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!


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
Re: resistance on groung rod #81983
10/10/02 11:07 AM
10/10/02 11:07 AM
T
txsparky  Offline
Member
Joined: May 2001
Posts: 552
Magnolia,.Texas U.S.A.
I think I'll go gather some worms and find that fishing hole Joe took a picture of [Linked Image]
Now where did I put that" 5amp worm gatherin tool " [Linked Image]


Donnie
Re: resistance on groung rod #81984
10/10/02 12:03 PM
10/10/02 12:03 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
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?

Re: resistance on groung rod #81985
10/10/02 07:33 PM
10/10/02 07:33 PM
HotLine1  Offline

Member
Joined: Apr 2002
Posts: 6,918
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


John
Re: resistance on groung rod #81986
10/10/02 07:54 PM
10/10/02 07:54 PM
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
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!

[Linked Image]

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).]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
Re: resistance on groung rod #81987
10/11/02 06:04 PM
10/11/02 06:04 PM
W
watthead  Offline
Member
Joined: Oct 2001
Posts: 172
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

Re: resistance on groung rod #81988
10/11/02 06:16 PM
10/11/02 06:16 PM
R
Roger  Offline
Member
Joined: May 2002
Posts: 1,716
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

Re: resistance on groung rod #81989
10/11/02 08:05 PM
10/11/02 08:05 PM
sparky66wv  Offline
Member
Joined: Nov 2000
Posts: 2,236
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?

[Linked Image]


-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI
Re: resistance on groung rod #81990
10/11/02 08:27 PM
10/11/02 08:27 PM
T
Tom Baker  Offline
Member
Joined: Oct 2001
Posts: 30
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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