Electrical Fault Current Calculator
Calculate symmetrical three-phase and single-phase-to-ground fault currents based on system voltage and source impedance.
Formulas
Three-Phase Symmetrical Fault:
Isc3 = VLN / Z = (VLL / √3) / √(R² + X²)
Single-Phase-to-Ground Fault (simplified):
Isc1 = VLN / Z = (VLL / √3) / √(R² + X²)
Total Impedance Magnitude:
Z = √(R² + X²)
Where: VLL = line-to-line voltage (V), R = resistance (Ω), X = reactance (Ω)
Assumptions & References
- Assumes a balanced three-phase system with a single source impedance.
- The three-phase fault formula uses the Thevenin equivalent: Isc = VLN / Z (IEEE Std 141 / Red Book).
- The single-phase-to-ground calculation assumes positive-, negative-, and zero-sequence impedances are equal (simplified model per IEEE Std 141).
- Motor contribution and arc impedance are not included in this simplified model.
- For more accurate results, use the full symmetrical components method (ANSI/IEEE C37.010).
- Results represent the initial symmetrical (subtransient) fault current magnitude.
- Reference: IEEE Std 141-1993 (Red Book), IEC 60909 Short-Circuit Currents.