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Earthing Design

Competent earthing design is a key component of substation safety.

Our earthing studies will ensure compliance with the Standards for:

  • step and touch potential,
  • earth fault-loop impedance limits,
  • sizing of protective earth conductors, earthing of conductive parts &
  • equipotential bonding.

For HV system earthing, AEE identifies the relevant generic case studies provided in Australian Standard, AS 2067:2016 to assess acceptable levels of step and touch potential.

For large earth grids, such as those associated with outdoor substations, AEE applies the theory provided in the North American standard, IEEE 80 Substation Grounding, to calculate the earth grid resistance. These results, in conjunction with short circuit studies and selection of an appropriate split factor, allow the calculation of the earth potential rise (EPR), step voltages and touch voltages associated with the earth grid.

Our design capabilities span the following types of earthing systems:

  • TN where the source’s earthable point and the equipment frames are connected to the same earth. This system has three sub types:
    • TN-C with a common cable (PEN) for both protective earth and neutral,
    • TN-S with separate protective earth (PE) and neutral (N) cables, &
    • TN-C-S where part of the system uses a PEN conductor but at some point there is a split into separate PE and N conductors.
  • TT where the source’s earthable point and the equipment frames are separately connected to earth. There is no earth conductor between the source and the (downstream) installations. At each installation, all exposed conductive parts of are connected to a local earth electrode.
  • IT where the source’s earthable point is connected to earth through a high impedance such as an earthing resistor or earthing reactor. The equipment frames are earthed to an earth electrode system which may be the same system used for earth the source’s earthable point.

AEE can also ensure that your low voltage circuits are protected to the requirements of clause 5.7 EARTH FAULT-LOOP IMPEDANCE as given in the Wiring Rules, AS/NZS 3000.