ToolStaxx guide
Earth fault loop impedance calculator explained
Estimate Zs from Ze and R1+R2, compare it to a chosen max Zs value, and understand the relationship between loop impedance and fault current.
Quick answer
Estimate Zs from Ze and R1+R2, compare it to a chosen max Zs value, and understand the relationship between loop impedance and fault current.
How to do it
- Zs is estimated as Ze + R1+R2.
- Lower impedance produces higher fault current.
- Use the correct protective-device data and correction factors for real work.
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.
When this is not suitable
Do not use this instead of proper testing, standards, competent judgement or safety-critical design checks.
Related next tools
Next useful power and electrical tools for this check.
Keep the result together
Use the calculator first, then add the result to a Project Sheet if you need a clean printable summary.
Open Project Sheet Builder