megger readings vs earth ground tester

[mannyb]

we have a customer that has changed the way we do ground testing. they required the grouding be done at each electrode with earth ground tester for ohms, now
they want a megger to test entire ground loop for tower ground of cellular site. I was wondering what the difference. the requirement is to be 5 ohms or less. IMO opinion if each ground rod test 5 ohms of less there should be a problem. does any one have experience with testing ground ring with megger tester or why one is needed.

 

[GoldDigger]

A simple Megger is designed for high voltage testing of resistances in the megohm and above range. It is not a ground impedance meter. There may also be a low impedance test function (low voltage, high current) but that by itself is not suitable for ground impedance testing.
If you do not use a clamp type meter for individual electrodes, the recognized alternative is the three point fall of potential method. But if you try to apply that to an entire GES you really need to have clear space several building diameters around the building for your test electrodes.

 

[mannyb]

A simple Megger is designed for high voltage testing of resistances in the megohm and above range. It is not a ground impedance meter. There may also be a low impedance test function (low voltage, high current) but that by itself is not suitable for ground impedance testing.
If you do not use a clamp type meter for individual electrodes, the recognized alternative is the three point fall of potential method. But if you try to apply that to an entire GES you really need to have clear space several building diameters around the building for your test electrodes.

i understand. i have read different literate and they say what you mention. i also understand that if used properly you will get same results. Clamp meter or megger using fall of potential method.

 

[jim dungar]

A simple Megger is designed for high voltage testing of resistances...

I have seen lots of field technicians refer to their test sets by the Manufacturer's name rather than the function they perform. This almost always ends up in confusion when they are not with their normal co-workers.
My ground test equipment is built by Megger, my high resistance meter comes from Fluke, my VOM is from Square D.

 

[brian john]

There is also confusion in what should be used for Earth Ground Resistance Testing, and have seen electricians trying to use a megger.

The question to the OP is what is the customers requirement, and that should be a low resistance ground that would be the complete grounding electrode ring, But to get the true resistance of this you would need to go out at a minimum of 10 times the diameter of the ring or diagonal

The clamp-on is generally not an accepted method by our customers.

In my experience most Ground Resistance test are not performed per properly.

 

[big john]

...In my experience most Ground Resistance test are not performed per properly.

No argument, but I will say I have seen a number of sites where it was literally impossible to do a proper FOP test.

 

[brian john]

No argument, but I will say I have seen a number of sites where it was literally impossible to do a proper FOP test.

I am with you there 110%. Often next to impossible, but customers refuse to accept that as an answer, they need a number to sign off on the project.

 

[cuba_pete]

we have a customer that has changed the way we do ground testing. they required the grouding be done at each electrode with earth ground tester for ohms, now
they want a megger to test entire ground loop for tower ground of cellular site. I was wondering what the difference. the requirement is to be 5 ohms or less. IMO opinion if each ground rod test 5 ohms of less there should be a problem. does any one have experience with testing ground ring with megger tester or why one is needed.

Seems a little backwards. I use the ground tester (FOP) for testing the health of the system, and use the Megger to determine resistance at higher potentials, such as when I am testing building steel as part of a LPS or downleads for the system. The results were actually the same, except where the resistances were out of range for the ground tester (too high).

I would normally use a megger for insulation testing, though.