ToolStaxx guide
How to calculate prospective fault current
Prospective fault current is commonly estimated from supply voltage and loop impedance. This guide explains the simple voltage ÷ impedance calculation and when to use the ToolStaxx PFC calculator.
Quick answer
Prospective fault current is commonly estimated from supply voltage and loop impedance. This guide explains the simple voltage ÷ impedance calculation and when to use the ToolStaxx PFC calculator.
How to do it
- Start with the measured or supplied Ze value.
- Use nominal voltage for a quick estimate, usually 230 V for UK single-phase domestic notes.
- Divide voltage by impedance to get amps, then divide by 1000 for kA.
- Record whether the value is estimated or measured.
Worked example
230 V ÷ 0.35 Ω = 657 A, or 0.66 kA.
Common mistakes
- Using an assumed Ze without checking.
- Confusing PSCC, PEFC and the highest prospective fault current.
- Recording an estimate where a measured value is required.
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