clamp-on ground resistance tester categories

[MIEngineer]

I am looking to purchase an AEMC 3711 tester for checking the integrity of existing facility ground. In comparing models I see that many have CAT III ratings. In my understanding of IEC 61010, without actually reviewing the document, the CAT ratings only apply for voltage testing with hazards resulting from transients. Why would these types types of meters have CAT ratings at all? Aren't the CAT IV ratings for outdoor environments anyway?

Thanks.

 

[brian john]

How do you plan to use this tester.

It is reliable only in very specific applications.

It is not recognized tester for ground measurements.

I own one and never use it. Not that has any bearing on anything.

Zog has more on this.

 

[zog]

I am looking to purchase an AEMC 3711 tester for checking the integrity of existing facility ground. In comparing models I see that many have CAT III ratings. In my understanding of IEC 61010, without actually reviewing the document, the CAT ratings only apply for voltage testing with hazards resulting from transients. Why would these types types of meters have CAT ratings at all? Aren't the CAT IV ratings for outdoor environments anyway?

Thanks.

Well you are outdoors and are working on an energized system and have a potential of transients.

As far as a clamp meter, you may want to look into that a little more, many issues and limitations on thier use. They do some slick marketing of them though.

 

[zog]

Limitations of clamp on ground testers

Effective only in situations with multiple grounds in parallel (pole grounds).

Cannot be used on isolated grounds (no return path)

Not applicable for installation checks / commissioning new sites

Cannot be used if an alternate lower resistance return exists not involving the soil

Subject to influence if another part of the ground system is in "resistance area"
? If there is another part of the ground system in the "resistance area" of the electrode under test, the result will be lower than the true resistance of the electrode ? this could lead to a false sense of security.

Requires a good return path:
? Poor return path may give high readings.

Connection must be on the correct part of the loop for the electrode under test:
? Requires thorough understanding of the system.
? Wrong connection can give a faulty result.

Susceptible to noise from nearby substations and transformers (no reading).

There is no built?in proof for the method ? results must be accepted on "faith". Most facilities will not accept a clamp on reading, nor does IEEE or ANSI recognize it as a valid test method.

 

[jim dungar]

Limitations of clamp on ground testers

Effective only in situations with multiple grounds in parallel (pole grounds).

What about confirming building steel 'bonding jumpers' to ground grid and equipment enclosures?

I understand these are not first choice devices, but sometimes isn't a quick and dirty check sufficient?
Dragging a reference conductor through an operating facility can be daunting. And sometimes finding undisturbed soil is all but impossible.

 

[MIEngineer]

Basically we have an older building that is having the service entrance and a room upgraded, more receptacles, lighting, new panelboard, etc. There is an existing bare ground connected at the main disconnect that is bonded to the building neutral. The bare wire goes into the footing and then disappears, no ground rods can be seem sticking above grade. The intent is to test this bare wire to see if it serves as a sufficient ground. Since we don't know of any ground rods I have a feeling we need to install a few anyway. We are also bonding the water service as well as the steel roof beams, walls are block.

So is it not even worth having the clamp-on tester for facility work?

Any insight into the CAT ratings?

Thanks for everyone's replies.

 

[zog]

What about confirming building steel 'bonding jumpers' to ground grid and equipment enclosures?

Point to to connections should be verified with a low resristanc eohmeter and should be less than 0.5 ohms

I understand these are not first choice devices, but sometimes isn't a quick and dirty check sufficient?

Yes, if applied correctly under the right conditions, but you still have no verification.

Dragging a reference conductor through an operating facility can be daunting. And sometimes finding undisturbed soil is all but impossible.

Amen to that, not always easy.

 

[zog]

Basically we have an older building that is having the service entrance and a room upgraded, more receptacles, lighting, new panelboard, etc. There is an existing bare ground connected at the main disconnect that is bonded to the building neutral. The bare wire goes into the footing and then disappears, no ground rods can be seem sticking above grade. The intent is to test this bare wire to see if it serves as a sufficient ground. Since we don't know of any ground rods I have a feeling we need to install a few anyway. We are also bonding the water service as well as the steel roof beams, walls are block.

So is it not even worth having the clamp-on tester for facility work?

Any insight into the CAT ratings?

Thanks for everyone's replies.

If there is a fault on the system the ground will be energized, hence the need for a CAT rating.

 

[jim dungar]

Point to to connections should be verified with a low resristanc eohmeter and should be less than 0.5 ohms

Yes, if applied correctly under the right conditions, but you still have no verification.

Point to Point is great when you have access to both points, but that is not always possible for 'quick checks' in existing installations.
Many facilities have bonding jumpers where one end disappears into the concrete and the other end may also not be readily accessible.

For example, say a customer puts a clamp-on ammeter around some jumpers and measure currents from .04A to 2.8A, he uses a clamp-on ground meter, in a different area, and finds (9) jumpers at .10 ohms, (1) @ .11 ohms, (1) @.02 ohms and (1) at .09 ohms. Are you saying nothing can be deduced from these types of quick checks? After all there is not specific ground resistance value required for NEC compliance.

 

[zog]

Point to Point is great when you have access to both points, but that is not always possible for 'quick checks' in existing installations.
Many facilities have bonding jumpers where one end disappears into the concrete and the other end may also not be readily accessible.

For example, say a customer puts a clamp-on ammeter around some jumpers and measure currents from .04A to 2.8A, he uses a clamp-on ground meter, in a different area, and finds (9) jumpers at .10 ohms, (1) @ .11 ohms, (1) @.02 ohms and (1) at .09 ohms.

How do you know what you are measuring? Without having a clear picture of the grounding system there is no way to properly apply a clamp on ground meter test.

Are you saying nothing can be deduced from these types of quick checks? After all there is not specific ground resistance value required for NEC compliance.

No, I am saying you have to know how to properly apply the test and still have to take the readings with a grain of salt because you can't verify the accuracy.

Here is an article on the limitations and proper application. http://www.netaworld.org/files/neta-journals/NWsu05-JOWETT.pdf

 

[jim dungar]

How do you know what you are measuring? Without having a clear picture of the grounding system there is no way to properly apply a clamp on ground meter test.

No, I am saying you have to know how to properly apply the test and still have to take the readings with a grain of salt because you can't verify the accuracy.

Here is an article on the limitations and proper application. http://www.netaworld.org/files/neta-journals/NWsu05-JOWETT.pdf

The article seems to be saying:
Clamp-on meters are 'not good' for measurements to actual ground/dirt.

Clamp-on meters can be 'good' for evaluating bonding.