Earthing conductor size for fault current
Size an earthing conductor for the fault current and compare five materials and tape dimensions.
Conductor operating conditions
One set of data for five materials.
This calculator is illustrative. All materials are calculated at once; click a card to see the details of one.
Illustrative calculator. Thermal calculation using the IEEE Std 80 formula; the formula accounts for the conductivity of the coating relative to copper. The selection covers the size table; it does not account for additional mechanical or corrosion requirements or the connection method. The result is for preliminary calculations and must be checked in the design and by measurement. It does not confirm that the installation complies with standards.
Formula, material properties and scope
A = I / √[TCAP · 10⁻⁴ / (t · α · ρᵣ) · ln((K₀ + Tₘ) / (K₀ + Tₐ))]
I — fault current in kA, t — fault duration in seconds, A — cross-section in mm². Constants for Cu, INOX and Fe/Zn come from IEEE Std 80, Table 1. For copper-bonded steel, ρᵣ = 9.67 µΩ·cm is taken from the calculator of the manufacturer this tool was built for (IEEE gives 8.62 for a 20% conductivity rod). Comparing all materials requires an initial temperature below 419°C. Scope of this tool: faults up to 5 s.
| Material | TCAP | α | ρᵣ | K₀ [°C] | Tₘ [°C] |
|---|---|---|---|---|---|
| Fe/Cu | 3.85 | 0.00378 | 9.67 | 245 | 1084 |
| Fe/Cu/Sn | 3.85 | 0.00378 | 9.67 | 245 | 1084 |
| Cu | 3.42 | 0.00381 | 1.78 | 242 | 1084 |
| INOX | 4.03 | 0.0013 | 72 | 749 | 1400 |
| Fe/Zn | 3.93 | 0.0032 | 20.1 | 293 | 419 |
The size is selected without rounding the result down. Table limits are inclusive, and the actual width × thickness area must be at least equal to the thermal result. “Out of range” means the required cross-section exceeds the largest tape in the size table; we do not invent larger sizes.