External Loop Impedance

The external loop impedance is the impedance of the path that the fault current takes external to the installation. The value can be measured using a test instrument. The Ze contributes to the overall earth fault loop impedance.


Zs                Earth fault loop impedance

Ze                External loop impedance

R1                Resistance of the line conductor

R2                Resistance of the CPC

Zs = Ze + (R1 + R2)

Measuring Ze

City & Guilds 2365

Electrical Installation