LoadCairn / Power & UPS
Available fault current calculator
Enter transformer size, three-phase secondary voltage, and transformer impedance to see the supplied planning equations with each input and calculation step in view.
Inputs
Adjust the estimate
Results update as you change a value. Calculations run in this browser.
Live results
Current estimate
Full-load amps
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Enter positive finite values for all three inputs.
Available fault current
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Enter positive finite values for all three inputs.
Fault MVA
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Enter positive finite values for all three inputs.
Formula and calculation trace
Full-load amps = kVA × 1000 / (√3 × V) · Available fault current = full-load amps / (%Z / 100) · Fault MVA = kVA / (%Z / 100) / 1000
Enter a transformer size, a positive three-phase secondary voltage, and a positive %Z.
Published source: Schneider Electric, FAQ FA105006 documents the three-phase full-load-current relation and transformer-secondary available-fault-current method.
Assumptions and limits
- infinite bus on the primary (utility contribution and motor contribution excluded — both raise the real value); planning estimate for gear-rating discussions only, not an arc-flash or coordination study.
estimates for planning only, not a substitute for a licensed engineer's design or manufacturer data.