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
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 (
When choosing between the methods or performing calculations, several variables must be considered: earth cable sizing
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 ($S_PE$).
To ensure safe and reliable earthing, the following best practices should be followed: The process of sizing these conductors ensures they
These systems often require larger bonding conductors because they may carry neutral current under certain fault conditions. Standard PME sizing tables often mandate a minimum of based on the incoming supply size.
The internationally accepted method (from IEC 60364 and BS 7671) is the . It assumes that during a short fault, no heat is lost to the surroundings—all heat stays in the conductor. IET Tables for k-factors provide these values
where k is a constant that depends on the cable material and Tmax.
According to IEC 60364-5-54, the cross-sectional area of the protective conductor (PE) can be determined either by referencing standardized tables or by calculation.