Plant ground testing frequency

[controlnovice]

Is there any code/recommendations for testing frequency of ground grids.

I'm not talking 50Hz vs 60Hz. I'm looking for a schedule frequency 6 months vs annually vs 5 years, etc.

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[Skogsgurra]

32 nHz seems reasonable. But that depends a lot on what your factory does. No vibrations, dry environment and other positive factors could easily reduce that to something like 6 nHz - as you said.

Sorry, couldn't resist.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[controlnovice]

There always has to be one

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[Zogzog]

It depends on the type of facillity, refer to the NFPA 70B. Should never exceed 3 years.

 

[ScottyUK]

Hi zogzog,

Some parts of the world don't use or much care about NFPA standards because we aren't governed by them. Can you quantify 'should never exceed three years' with any data to support the choice of three instead of (say) one year or five years?

For example, doing a proper test on the fully welded copper earth grid at our power plant would require a full station outage because of the amount of noise in the ground which consistently foils any attempt at measuring earth grid resistance into the bulk of earth. The earth grid is also heavily tied to two major transmission substations which makes things even harder to test. Three yearly testing simply isn't going to happen. We just about manage to maintain visual inspection of the thousands of above ground connections to the structural steel at five yearly intervals. We prove earth connections from the switchgear and other major electrical plant to the earth grid much more frequently, at roughly two year intervals.


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Sometimes I only open my mouth to swap feet...

 

[Zogzog]

No idea on the basis of the 3 year recommendation from the NFPA 70B. Ground testing is highly debated here in the US also, some people believe it should be done every year and is vital to safety and the operation of some types of ground fault protection, others believe there is no reason to ever test.

I think that you should always perform a fall of potential test on a new installation, and then retest if you suspect there may be a problem due to water table changes, people getting shocked off equipment, failure of a GF relay, etc. But that is just my 2 cents.