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Earthing System Design

An earthing system has to do two things at once: keep step and touch voltages within safe limits during a fault, and give fault current a reliable path so protection operates. Both depend on soil resistivity, which is why the design starts with measured data rather than assumed values.

What this covers

  • Soil resistivity interpretation — deriving a layered soil model from measured field data.
  • Earth grid design — conductor layout, spacing, depth and rod arrangement.
  • Step and touch voltage — calculated against tolerable limits for the fault duration and surface layer used.
  • Ground potential rise — magnitude and the transferred potential implications for incoming services and communications.
  • Conductor sizing — thermal sizing of earth conductors for the fault duty and duration.
  • Earthing arrangement — solid, resistance or resonant earthing and the fault current each produces.
  • Lightning and surge — coordination with lightning protection and surge arrester earthing.

What you receive

  • Earthing design report with the soil model and calculation basis
  • Earth grid layout drawings
  • Step, touch and ground potential rise calculations against tolerable limits
  • Conductor sizing calculations
  • Test and verification requirements for commissioning

Standards and references

Design is carried out to IEEE 80 for substation earthing and IEC 61936-1 for AC installations above 1 kV, with soil measurement to IEEE 81 and conductor sizing to IEC 60949.

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