[ S = \frac\sqrtI^2 \times tk ]
When a fault occurs (say, a live wire touches a metal casing), the earth cable must carry the full fault current until the protective device (breaker or fuse) trips. During that short time—milliseconds to a few seconds—the earth wire heats up. earth cable sizing
If it’s oversized unnecessarily:
The process of sizing these conductors ensures they can safely carry fault current for a specific duration until the protective device (like a circuit breaker or fuse) disconnects the circuit. 1. Two Main Sizing Methods [ S = \frac\sqrtI^2 \times tk ] When
For most common installations, standards provide a direct correlation between the cross-sectional area of the Phase Conductor ($S_ph$) and the Protective Earth Conductor ($S_PE$). IET Tables for k-factors provide these values
Copper is the standard, but aluminum or steel (like cable tray or conduit) requires a larger cross-section due to lower conductivity. IET Tables for k-factors provide these values. Fault Current (