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Hi Slamat,

Thank you for your question regarding resistance-to-ground calculations for parallel electrodes, it is our pleasure to help.

The simplified calculation for predicting the resistance-to-ground (earth) of a given length grounding rod is:

R=(p/(2*pi*L))*(ln*(4L/a)-1)) + (p/(2*pi*s))*(1-(L squared/3s(10X8)) + (2L(10×4)/5s(10×4)…)

Where:

• R= Resistance
• p= soil resistivity
• L = Length of the rod
• a= radius of the rod
• ln= natural log
• s = rod spacing

The above is the hand formula, however it does not take into account multi-layered soils.  We highly recommend using a computer program such as CDEGS.  Here are a few other links that you may find useful:

http://www.esgroundingsolutions.com/blog/731/we-have-soil-resistance-in-260-ohm-meter-short-circuit-level-is-8000a-short-circuit-time-3-milli-second-i-want-to-calculate-the-length-of-copper-rod-dia-how-many-earth-pit-required-and-depth-o

http://www.esgroundingsolutions.com/blog/664/what-are-calculations-regarding-lowering-earth-resistance-using-copper-rods-tapes-at-telecom-tower

We hope you find this information useful.  If you should have any further questions. Please do not hesitate to contact us again in the future.

Best regards,

The Engineering Team at E&S Grounding Solutions

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