Recommended Standard Size: mm²
This earth conductor size calculator is an essential tool for electrical engineers and technicians. It helps determine the minimum safe cross sectional area required for an earthing or grounding wire. Using the adiabatic equation ensures that your safety cables can carry massive short circuit fault currents without melting before the circuit breaker trips.
Earth Conductor Size Formula
The calculation relies strictly on the standard adiabatic equation recognized by international electrical codes. The formula evaluates the thermal stress applied to the cable during a sudden electrical fault.
S = (I x √t) / k
Where:
- S represents the minimum required cross sectional area in square millimeters.
- I represents the estimated fault current measured in Amperes.
- t represents the operating time of the protective device measured in seconds.
- k represents the material constant factor based on the metal and insulation type.
Conductor Material Constant (k)
The k factor is a predefined thermal constant. It assumes initial and final safe temperatures for different materials. Copper wire with standard PVC insulation generally uses a k factor of 143. Using XLPE insulation raises the safe temperature limit and allows a k factor of 176. Bare copper wire lacks melting insulation limits and uses a k factor of 228.
Common Earth Conductor Size Conversions
| Fault Current (A) | Duration (s) | Material Type | Min Area (mm²) | Standard Size (mm²) |
|---|---|---|---|---|
| 5000 | 0.5 | Copper PVC | 24.72 | 25 |
| 5000 | 1.0 | Copper PVC | 34.97 | 35 |
| 10000 | 0.5 | Copper PVC | 49.45 | 50 |
| 10000 | 0.5 | Copper Bare | 31.01 | 35 |
| 15000 | 0.2 | Copper XLPE | 38.14 | 50 |
| 20000 | 0.5 | Aluminum PVC | 148.86 | 150 |
| 25000 | 1.0 | Steel Bare | 320.51 | 400 |
| 30000 | 0.1 | Copper PVC | 66.31 | 70 |