Ground System Testing Requirements

[mdgardner]

I have a client (manufacturing facility) looking for how often they should be testing their grounding system and what kind of testing they should be doing? I've found a lot of information on testing ground resistance. Is this all that all the testing that is required? what about maintenance of connections, etc? How often should these be checked?
Thanks!

 

[petersonra]

Why would you test something like that at all? Do a visual inspection annually. That is about all that is needed unless you have something very special like a cell tower.

If the customer wants to spend money for no good reason there are all kinds of tests that can be done.

 

[mayanees]

In accordance with NETA there's a test for it, Acceptance and Maintenance tests. In the 2015 version of the Maintenance Testing Specification it's section 7.13 Grounding Systems. There are point to point tests, along with a Fall of Potential (FOP) test on the assembled system. The minimum acceptable limits for the FOP test for industrial/commercial systems is 5 ohms and it's less than 1 ohm for generating/transmission systems.

I used to require it on our biannual Power System PMs when I worked in industry where all of the electrical systems were maintained in accordance with industry standard. Scott Paper and P&G both support maintenance for electrical systems. And it's the only way that arc flash labels are applicable, if the electrical equipment maintenance is to industry standard. So corporate-conscious employers keep their electrical systems maintained.

 

[nhee2]

And it's the only way that arc flash labels are applicable, if the electrical equipment maintenance is to industry standard. So corporate-conscious employers keep their electrical systems maintained.

Is this correct? I understand the need for maintenance of OCPDs, I guess I would not have considered ground system testing a requirement for validating results of an arc flash study - don't all the arc-flash calculations assume L-L faults?

 

[mayanees]

Is this correct? I understand the need for maintenance of OCPDs, I guess I would not have considered ground system testing a requirement for validating results of an arc flash study - don't all the arc-flash calculations assume L-L faults?

I'm referring to ocpd testing to put the system into the "Normal" category in 70E, so I don't think ground-testing would negate that classification. But ground testing would be part of a comprehensive Power System PM.

 

[zbang]

One thing often neglected IF you have an isolated-ground setup is to make sure that it's still isolated. Usually this meant that during a full downtime, the factory electricians would de-energize a branch circuit, lift the IG conductor, and test continuity to the GES; if there was, they'd start at the far end and work back looking for something that would cause the fault. Called it "ground-hogging" .