Ground rod testing

[easymoney]

We are testing our ground rods at out facility with a fluke clamp on meter. On some of the transformers 480/120 we get "noise" or current on the test, why is this? how can it be fixed?:-?

 

[ceb58]

We are testing our ground rods at out facility with a fluke clamp on meter. On some of the transformers 480/120 we get "noise" or current on the test, why is this? how can it be fixed?:-?

The clamp meter method is unreliable. The "noise" usually means that it is detecting a grounding loop. As in one big ground ring. The only way to achieve a true idea is preforming a F.O.P. test (fall of potential). If this is a one time thing you would be better off hiring some one to do this test for you due to the cost of the equipment.

 

[dereckbc]

We are testing our ground rods at out facility with a fluke clamp on meter. On some of the transformers 480/120 we get "noise" or current on the test, why is this? how can it be fixed?:-?

It is happening because there is current flowing, and perfectly normal. It can also be from improper wiring which can be fixed.

 

[brian john]

The clamp on should also measure current, did you measure current?

Did they bond XO in the transformer and panel? this will result in ground current.

Do you have a high number of switch mode power supplies? this can result in noise.

If you have ground current you may have a shorted neutral conductor down steam from the XMFR or you may have neutrals cross connected between transformers.

 

[dereckbc]

Is it a grounded service like wye or corner grounded delta?

 

[augie47]

With the Fluke clamp-on, if you disconnect the grounding electrode conductor from it's termination (panel, transformer, etc) can you measure the resistance of just that one electrode by clamping the non-terminated GEC ?.

 

[don_resqcapt19]

With the Fluke clamp-on, if you disconnect the grounding electrode conductor from it's termination (panel, transformer, etc) can you measure the resistance of just that one electrode by clamping the non-terminated GEC ?.

No, the rod has to be connected to the system for any of the clamp-on ground resistance testers to work.

 

[hardworkingstiff]

No, the rod has to be connected to the system for any of the clamp-on ground resistance testers to work.

How do they work Don, by using the coil to introduce a current into the ground conductor and then check the resistance of the conductor by how much the coil field changes?

If so, then isn't it really checking the ground rod connection to the grounded PoCo system?

 

[don_resqcapt19]

Lou,
They inject a high frequency current into the electrode and measure the voltage drop, but not exactly sure how it all works.

 

[sparky_magoo]

I recently added a 125 amp subpanel to a house and dicovered that the ufer was never connected to the panel when I opened the wall to install the new feeder. I measured 23 Ohms from the # 4 stub to the meter-main cabinet.

Was this an accurate indication of the ufer's impedance? If it wasn't an accurate measurement, why not?

 

[ohmhead]

Well it works by a current electrode and a potential electrode placed at a distance from the rod under test .

The tester has two rods testing rods these measure the current and voltage back to the rod under test or system under test by a higher frequency then 60 cycles mostly at 97.5 hertz . Then the voltage and current in ground between rods back to test rod gives us ohms in resistance there placed apart at say 50 foot voltage rod to 90 foot current rod so the fields around the rods dont overlap .

It measures the R=E/I and calculates this in the old days it was a galvanometer but today its a digital circuit to find ohms.

Its at a high freq to keep stray freq of electrical equipment on systems from effecting the meter .

 

[ohmhead]

Well read this it explains it in detail both methods clamp and three point or four point http://www.lyncole.com/pdf/Lyncole_Ground_Test_Methods.pdf