Earth resistance measurement

By Manuel Jaime Leibovich

Abstract:

The main factors that should be considered in order to get an accurate earth resistance measurement in electrical systems are analyzed. The measurement system geometry, including minimum distances that should be taken into account, is particularly considered.

Introduction:

The grounding system is an essential element for the electrical system security and it is required to:

  • Allow for protective devices activation when there is an insulation fault.
  • Equalize the potential of conductive parts that can be accessed simultaneously, with the potential in the surrounding soil in order to prevent people from being exposed to hazardous voltages.
  • Allow the lightning strike energy to be safely dissipated.
  • Reduce electromagnetic interferences.

Due to the fact that it is a system designed to guarantee safety, its effectiveness should be verified. The diffusion resistance value is the parameter normally considered to be the most relevant one to test grounding system quality and its capacity to carry out its function properly. But the correct measurement of this parameter needs to fulfill several requirements, which will be analyzed in this issue.

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