Power & Electrical
Earth Fault Loop Impedance Calculator
Estimate Zs from Ze and R1+R2, compare it to a maximum Zs value and show calculated fault current.
Estimator only. Use the correct maximum Zs for the protective device, standard, temperature correction and local requirements.
Notes and next steps
How it works
Estimate earth fault loop impedance Zs from Ze and R1+R2, with a simple max Zs comparison.
Formula used: Zs = Ze + (R1+R2). Fault current = voltage ÷ Zs.
Worked example
Ze 0.35 Ω + R1+R2 0.42 Ω gives Zs 0.77 Ω. At 230 V, fault current is about 299 A.
Common mistakes
- Using an incorrect max Zs value.
- Ignoring temperature correction or protective device requirements.
- Treating an estimate as a test certificate result.