Skip to content
Open calculators

Transformer Terminal Fault Current Estimate

Estimate transformer full-load current and transformer-only symmetrical RMS terminal fault current from nameplate rating, secondary voltage and percent impedance.

Inputs

Transformer nameplate data

Choose single phase or three phase; three-phase secondary voltage is line-to-line.

Range: 0.1–100,000 kVA

Enter the transformer nameplate apparent-power rating.

Range: 1–100,000

Use line-to-line voltage for three-phase mode and secondary supply voltage for single-phase mode. Australian examples include 230/240 V and 400/415 V.

Range: 0.01–100 %

Enter the nameplate or test value. No typical impedance is assumed by the calculation.

Result

Estimated terminal fault current (A RMS symmetrical)
12,028
Estimated terminal fault current (kA RMS symmetrical)
12.028
Transformer full-load current (A)
721.69

Formula

Calculation logic

Formula definitions and substituted values.

Before relying on the result

  • Checking prospective fault current at a transformer secondary
  • Comparing equipment interrupting ratings with a transformer-only estimate
  • Compare the terminal estimate with manufacturer and supply-authority fault data before selecting equipment.

Related calculators

Compare the terminal estimate with manufacturer and supply-authority fault data before selecting equipment.