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Is there a way to determine the sphere of influence for a ground plate like there is for a ground rod?

Hi John,

Thank you for your question regarding the sphere of influence for a ground plate, it is our pleasure to help.

Yes, the sphere of influence of a ground plate is very easy to calculate.  Take the diagonal distance of the plate, and that is your length and then apply it to the standard formula.  Here is a link to that formula:

http://www.esgroundingsolutions.com/about-electrical-grounding/grounding-electrode-sphere-of-influence.php

The National Electrical Code has a requirement for ground plates in Article 250.52 (A)(7).  This code requires the thickness of the plate to be at least 6.4 mm (0.25 inch) for ferrous materials or 1.5 mm (0.06 inch) for non-ferrous materials, and the surface area to be at least 2-ft square.  This converts to 288 square inches or a 17-inch X 17-inch plate.  A 17 inch X 17 inch plate has a diagonal length of 24 inches (or 2-ft).  If we apply this to our sphere of influence formula we get approximately 40 cubic feet of soil for the sphere of influence.  Compare this to a 10-ft grounding rod, which utilizes 5,000 cubic feet of soil, a 125-times improvement.

Grounding plates are rarely the best choice for providing effective grounding because their sphere of influence is so small.  They also tend to cost more to purchase and to install compared to a standard grounding rod.

We hope that you find this information helpful.  If you should have any further questions, please do not hesitate to ask.

Best regards,

The Engineering Team at E&S Grounding Solutions

 

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