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How do you determine the resistance-to-ground of an active utility substation in an urban setting?

Scott asks us: Customer wants a fall of potential tests performed on the ground grid of a 34.5kv substation property. The problem is there is no soil around the property only asphalt. And within 50-75 feet on all sides of the property are other buildings. So there is no way to get out of the sphere of influence of the grid if there was soil to drive rods into. Is there an alternative test we can offer under this condition?

Hi Scott,

Thank you for your question regarding resistance-to-ground (fall-of-potential) testing of your substation, it is our pleasure to help.

Yes, the best way is to conduct a Wenner 4-point soil resistivity test in an open field somewhere near the substation, and then model the grid in a computer using the famous CDEGS engineering software. This is actually the single most common way to determine not only the resistance-to-ground of the substation, but the impedance-to-ground, and the mandatory human safety requirements under 29CFR1910.269 (Step & Touch Voltage hazards).

CDEGS is the software used by the IEEE, the NEC, the NFPA (and many more), to develop standards and regulations related to electrical safety and grounding and is the single most validated software on the market.  In fact, the programmers of the CDEGS program are some of the same people who developed the procedures used for the fall-of-potential test.

E&S Grounding Solutions can easily help you with this project.  If you would like some additional information regarding these services, please call us at 310-318-7151 California time, and someone will be happy to discuss your project with you.

Best regards,

The Engineering Team at E&S Grounding Solutions


Photo credit: E&S Grounding Solutions

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