Most international standards adopt the adiabatic equation for earth conductor sizing. BS 7671 (IET Wiring Regulations) provides the clearest formulation.
This is the most critical—and often most uncertain—value. For TN systems: earth cable size calculation
accounts for the electrical resistivity, temperature coefficient, and heat capacity of the conductor material. Standard values for under typical conditions include: Conductor Material Insulation Material Max Temperature ( ∘Craised to the composed with power C 143 Copper XLPE / EPR 176 Copper Bare (Uninsulated) 138 Aluminium 94 Aluminium XLPE / EPR 116 2. Step-by-Step Adiabatic Calculation Example earth cable size calculation