Enter the external earth loop impedance, and the resistance of the line and protective conductors, R1 and R2, into the calculator to determine Zs.

ZS (Earth Loop Impedance) Formula

The following equation is used to calculate the ZS (Earth Loop Impedance).

Zs = Ze + (R1 + R2)

  • Where Zs is the line-earth loop impedance
  • Ze is the external earth loop impedance
  • R1 is the resistance of the line
  • R2 is the resistance of the protective conductors

What is a ZS (Earth Loop Impedance)?


An earth fault loop impedance, denoted Zs, is a measure of the impedance along the path followed by a fault current when a low impedance fault occurs between the earth and a conductor.

How to Calculate ZS (Earth Loop Impedance)?

Example Problem:

The following example outlines the steps and information needed to calculate ZS (Earth Loop Impedance).

First, determine the external earth impedance. In this case, this value is measured to be 50 ohms.

Next, determine the resistance of the line. For this example, this is measured to be 20 ohms.

Next, determine the resistance of the conductor. This is determined to be 10 ohms.

Finally, calculate the line-earth impedance Zs, using the formula above:

Zs = Ze + (R1 + R2)

Zs = 50 + (20 + 10)

Zs = 80 ohms