Earthing Conductor Size Calculator

Calculate protective earth conductor size, grounding wire size and adiabatic short-circuit withstand from fault current, clearing time, material and insulation type.

⚡ Field Rule: Earthing conductor size is not selected by normal load current. It must withstand fault current until the protective device trips. Use this with the future Short Circuit Current Calculator, future Cable Derating Calculator, Conduit Fill Calculator, Cable Tray Fill Calculator and Breaker Size Calculator.

⏚ Fault Current Path — Protective Earth Conductor Sizing

Fault Current

Clearing / Trip Time

Conductor Material

k Factor

Installation Margin

Standard Size Series

Phase Conductor Size Optional

Adiabatic equation: S = √(I²t) / k. Use RMS fault current and actual protective device clearing time.

Presets:small DBmotor feedermain panel

Selected Earth Conductor Size

Fault Current

Clearing Time

k Factor

Phase Conductor Size Optional

This tab checks whether a selected earth conductor size can withstand the entered fault duty.

Earth Conductor Size

Clearing Time

k Factor

Safety Margin

This estimates the maximum fault current a conductor can withstand for the selected clearing time.

📐 Formula Reference

Adiabatic Equation

S = √(I² × t) ÷ k

Fault Withstand

Imax = k × S ÷ √t

Where S

S = protective conductor area in mm²

Where k

k depends on conductor material, insulation and temperature limits

📋 Quick Reference

Common k Factors

Copper PVC115

Copper XLPE143

Aluminium PVC76

Input Quality

Fault currentRMS

Trip timedevice curve

Materialcorrect k

Also Check

Touch voltagesite

Loop impedancefault path

Mechanical min.code

📚 Engineering Notes

Earth conductor is fault-duty basedPE conductor sizing depends on fault current and disconnection time, not normal operating current.

Use actual trip timeBreaker/MCCB/fuse clearing time from curves is important. A longer clearing time requires a larger conductor.

Short-circuit estimate comes firstUse the future Short Circuit Current Calculator to estimate fault current before sizing the earth conductor.

Installation checks still matterAfter sizing, check routing with the Conduit Fill Calculator or Cable Tray Fill Calculator, and use future Cable Derating Calculator where applicable.

What is an Earthing Conductor Size Calculator?

An earthing conductor size calculator estimates the minimum protective earth or grounding conductor cross-section needed to withstand short-circuit fault current until the protective device disconnects the circuit.

How protective earth conductor size is calculated

This calculator uses the adiabatic equation S = √(I²t) / k. Fault current, clearing time and conductor material factor decide the required cross-sectional area.

Earthing conductor sizing workflow

First estimate fault current with the future Short Circuit Current Calculator. Check the protective device trip time using the breaker/fuse curve. Then size the protective conductor with this calculator. For routing, use the Conduit Fill Calculator or Cable Tray Fill Calculator.

Important limitation

This calculator is a planning aid. Final earthing design must follow local electrical code, IEC/NEC/BS/IS requirements, minimum mechanical sizes, bonding rules, fault loop impedance, touch voltage, soil/earth resistance and protective device curves.

❓ Frequently Asked Questions

Usually no. Protective earth conductor sizing is mainly based on fault current and disconnection time, plus code minimums and mechanical requirements.

k factor represents the conductor material and insulation temperature limits used in the adiabatic short-circuit withstand equation.

No. Use it as a planning calculator only. Final sizing must follow applicable code, protective device data and project specifications.