| Motor Type | Contribution Multiplier | | :--- | :--- | | Induction (≤ 50 HP) | 4 × Motor FLA | | Induction (> 50 HP) | 5 × Motor FLA | | Synchronous | 6 × Motor FLA | | All Motors (Rule of thumb) | | 5. Conductor Impedance (Long Runs) For faults far from the transformer, conductor impedance significantly reduces fault current.
$$I_fault = \fracV_LL\sqrt3 \cdot (Z_transformer + Z_conductor)$$ available fault current formula
These formulas give symmetrical RMS current . For equipment interrupting rating (e.g., circuit breakers), you may need asymmetrical (peak) current, which is typically $1.6 \times I_symmetrical$ for low-voltage systems. | Motor Type | Contribution Multiplier | |