3 point fall of potential test question

[PowerdT]

Not what I was asking for. The job contract submittals or specifications describing what tests are required to be performed.

There is no job contract or anything. I just saw it in the manufacture user manual. That’s why it throws me off because It didn’t make sense to me

 

[ATSman]

What does not make sense? The test is measuring the resistance of the Ground Electrode (yellow) to earth after it is disconnected (isolated) from the rest of the ground system.

 

[PowerdT]

What does not make sense? The test is measuring the resistance of the Ground Electrode (yellow) to earth after it is disconnected (isolated) from the rest of the ground system.

Ok. Please correct me if I am wrong.

When u you do 3-point earth resistance test, you need 3 electrodes and probes to create electrical circuit, which are 2 auxiliary rods and 1 electrode(rod) that is under test.

Let’s say this rod under test is the service entrance electrode.
Do you disconnect the rod to measure 3-point test ?

 

[ptonsparky]

Ok. Please correct me if I am wrong.

When u you do 3-point earth resistance test, you need 3 electrodes and probes to create electrical circuit, which are 2 auxiliary rods and 1 electrode(rod) that is under test.

Let’s say this rod under test is the service entrance electrode.
Do you disconnect the rod to measure 3-point test ?

Yes, you disconnect the rod being tested from the rest of the GES. Two or more rods could checked at the same time but they, as a unit, would be disconnected from the rest of the GES.

 

[kwired]

I think I am mixed up with the Megger insulation. However, you answered my question. Another question related to this.

When you measure earth electrode resistance, would that make big difference on the test result when the rod is connected and disconnected?

Megger is actually brand name of testing equipment somewhat well known for insulation resistance testing equipment though they have other products.

Because of this many people call any insulation resistance tester a "Megger".

 

[PowerdT]

Yes, you disconnect the rod being tested from the rest of the GES. Two or more rods could checked at the same time but they, as a unit, would be disconnected from the rest of the GES.

Then this probably requires power outage.

I see what you mean though, if the tested rod still connected to the transformer GEC, the current injected from the earth tester might travel to the source

 

[ptonsparky]

Then this probably requires power outage.

I see what you mean though, if the tested rod still connected to the transformer GEC, the current injected from the earth tester might travel to the source

Not so much that it travels to the source but you would include every rod, every CEE, every waterline, etc. in that test. Your results would be meaningless.

 

[PowerdT]

Not so much that it travels to the source but you would include every rod, every CEE, every waterline, etc. in that test. Your results would be meaningless.

Yea that makes sense specially if you have bad ground result. However though if you test the ground without disconnecting and resulted a good ground then you should be good,

 

[roger]

My question is why bother? In a situation where a rod is or rods are the sole GE what could be so important that a rod type GE would require testing for a minimum or maximum. In commercial or industrial scenarios odds are there will be more than the rod(s) so who cares.

 

[PowerdT]

My question is why bother? In a situation where a rod is or rods are the sole GE what could be so important that a rod type GE would require testing for a minimum or maximum. In commercial or industrial scenarios odds are there will be more than the rod(s) so who cares.

Good question Roger. It’s for electronic equipment building where the ground resistance is required to be 5 ohms or less per IEEE 1100

 

[ptonsparky]

Who cares? The engineer that specs the tests in the bid contract!.

 

[PowerdT]

Who cares? The engineer that specs the tests in the bid contract!.

Maybe you are right who cares. I just wanted to learn and understand

 

[kwired]

Good question Roger. It’s for electronic equipment building where the ground resistance is required to be 5 ohms or less per IEEE 1100

I guess then you need to know whether that standard is test of the GES only or if it can include a GEC that is connected to the grounded service conductor. You should get different result with each of those scenarios nearly every time.

To some extent I don't get why they would want it to be a test with isolated GES though that is kind of what those electronics experts seem to want you to do when there is issues that they think grounding changes will fix, but isolating the ground from the service grounded conductor goes against NEC, and can leave you with voltage on equipment when there is a ground fault condition.