What This Calculator Is For
Use this calculator when you know the available fault MVA at a bus and want the corresponding balanced three-phase fault current. It is useful for breaker duty checks, transformer studies, and quick fault-level conversions.
Enter Fault Level
Formula
Isc = Fault MVA × 1000 ÷ (√3 × kVLL)
The result is symmetrical RMS current in amperes for a balanced three-phase fault.
Examples
Example 1
500 MVA at 13.8 kV
Isc = 500 × 1000 ÷ (1.732 × 13.8)
Isc = 20.92 kA
Example 2
250 MVA at 4.16 kV
Isc = 250 × 1000 ÷ (1.732 × 4.16)
Isc = 34.73 kA
Example 3
1000 MVA at 34.5 kV
Isc = 1000 × 1000 ÷ (1.732 × 34.5)
Isc = 16.74 kA
Limitations
This conversion does not determine asymmetrical peak current, X/R ratio, DC offset, interrupting duty, or contributions over time from motors and generators.
Equipment duty evaluation requires the correct study method, fault type, operating configuration, and applicable standard.