Short Circuit Current Calculator
Estimate the prospective short-circuit current at a point in the electrical system from transformer and cable impedance.
Short Circuit Current
12,028 A
Short Circuit Current vs Transformer Rating
Estimating Short Circuit Current
The maximum short-circuit current at a transformer secondary determines the required interrupting capacity of protective devices.
Formula
I_sc = I_fla / (Z% / 100)
Where I_fla is the transformer full-load secondary current and Z% is the transformer impedance.
I_fla (3-phase) = kVA x 1000 / (sqrt(3) x V_secondary)
This gives the maximum available fault current at the transformer terminals. Downstream cable impedance reduces the fault current at the load.
Example Calculation
500 kVA transformer, 5% impedance, 480 V secondary.
- 01FLA: 500,000 / (1.732 x 480) = 601.4 A
- 02I_sc: 601.4 / 0.05 = 12,029 A = 12.0 kA
- 03Available SC kVA: 500 / 0.05 = 10,000 kVA
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