Short Circuit Current Withstand
When a dead short occurs, massive current flows until the breaker trips. The wire must have enough thermal mass to absorb this energy without the insulation melting.
The I²t Formula
Based on the adiabatic heating equation (ICEA standard):
I = A × [K / √t]
- I: Short circuit current (Amps)
- A: Conductor area in circular mils (cmil)
- t: Clearing time of the breaker/fuse (seconds)
- K: Constant based on insulation type
K Constants (Copper)
| Insulation Type | Max Temp Allowed (°C) | K Value |
|---|---|---|
| Thermoplastic (PVC) | 150°C | 0.0297 |
| Thermoset (XLPE, EPR) | 250°C | 0.0428 |