Short Circuit Current Calculator

Calculate available fault current at downstream equipment.

Source Data

Calculation Method

Transformer kVA

Impedance (%Z)

Secondary Voltage

Phase

Conductor Run (Optional)

Conductor Length (ft)

Conductor Size

Conductor Material

Conduit Type

Short Circuit Formulas

Three-Phase SCC at Transformer:


                            Isc = (kVA x 1000) / (V x 1.732 x %Z/100)

Simplified Point-to-Point:


                            Isc2 = Isc1 / (1 + (f x L / C))

f = factor based on voltage, L = length (ft), C = conductor constant

NEC Requirements for Short Circuit Ratings

NEC 110.9

Equipment intended to interrupt current must have an interrupting rating not less than the nominal circuit voltage and current to be interrupted.

NEC 110.10

Equipment must be selected and coordinated to clear a fault without extensive damage to the electrical equipment.

NEC 409.110

Industrial control panels must be marked with short-circuit current rating and the protection must not exceed this rating.

Important: Equipment AIC ratings must equal or exceed available fault current. Series-rated systems may allow lower-rated downstream equipment when properly coordinated.