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What will be effect of adding a ground rod or horizontal grounding conductor on step and touch voltage and especially on GPR at a substation? Which option should be considered as far as design modifications are necessary?

Hi K A Vyas,

Thank you for your question regarding Step & Touch Voltages and the effect changes in the grounding system will have on human fibrillation currents.  It is our pleasure to help.

It is really not possible to predict the impact that changes to the grounding system will have on human safety, without running those changes through a computer model.  Here are a couple of things to keep in mind:

  1. Touch voltages are primarily mitigated by bringing the grounding systems (and thus the voltages) closer to the persons feet, so as to reduce the voltage differentials
  2. Step voltages are primarily mitigated by taking the grounding systems away from the persons feet, so as to keep the hazardous voltages away from the persons legs.
  3. Increasing grounding causes more current to flow in that area
  4. If the soil gets more resistive with depth, ground rods will not be as effective as horizontal grounding conductors at removing hazardous currents.
  5. If the soil gets less resistive with depth, ground rods will be more effective than horizontal conductors at removing hazardous currents.
  6. Ground rods tend to move hazardous currents away from the surface where people are at
  7. Horizontal grounding conductors tend to keep hazardous currents near the surface where people are at

As you can see by the list from above, many of the items seem contradictory to each other.  Adding a horizontal ground conductor may fix a touch voltage issue, but may cause a step voltage problem.  A driven ground rod may fix a step problem, but cause a touch problem.   The only way to know what the impact changes to the grounding system will have on human safety, is to run a computer simulation (model).  There are simply too many variables to analyze without the aid of a computer.  Also, given the legal implications found in many countries (29 CFR 1910.269 in the USA), it may also be the only legal way as well.

We here at E&S Grounding Solutions are more than happy to help you with conducting a computer model of your site.  But if not us, please get someone with the proper software and expertise to ensure that personnel working in the facility will be safe from electrocution.  Feel free to call us at 310-318-7151 California time.

Best regards,

The Engineering Team at E&S Grounding Solutions

 

Photo credit: E&S Grounding Solutions

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