Calculate EPR Contours

Modified on Thu, 20 Jul, 2023 at 4:23 PM

During an earth fault, the fault current which enters the earthing grid causes the grid voltage to rise. The subsequent voltage transferred to (conducted through) the soil is called Earth Potential Rise (EPR). The EPR reduces with distance as we move away from the earthing grid. The EPR can represent a hazard when transferred to nearby sensitive locations.

In certain countries, there are safety limits for the EPR, which can be transferred on particular assets via earthing systems whilst dissipating earth fault currents. The Standard AS/NZS 3835.1, which relates to telecommunications assets, provides certain rules for the EPR limits, and these limits are as follows:

Telecommunications EPR - Code of Practice, Section 4.2:

  • 430 V EPR contour
  • 650 V EPR contour
  • 1500 V EPR contour
  • 2500 V EPR contour


These EPR contours can be plotted using SafeGrid Earthing Software as follows.

Step 1:    Configure the Voltage Profiles to extend beyond the earthing system boundary.

You can create a large area profile and/or a long-line profile. In the image below, both have been created to extend 100 metres beyond the perimeter of the earthing grid.

Step 2:    Calculate in Display Results.

Step 3:    Plot and analyse the EPR contours.

1. Enter the EPR limit into the Surface voltage limit.

2. Press Exceeding limit.

The 3D EPR contour is displayed below.

You can switch to a 2D contour surface view.

You can switch to a 2D contour line view.

There is a Line profile, and the Surface voltage limit is shown on the plot.



[1]    AS/NZS 3835.1:2006  Earth potential rise - Protection of telecommunications network users, personnel and plant.

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