Short-Circuit Current Calculator

Inputs

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Three-phase uses line-to-line voltage and sqrt(3). Single-phase uses the entered voltage and loop impedance.
Infinite source ignores upstream impedance. Known source adds an upstream Thevenin impedance on this voltage base.
Transformer apparent-power rating in kVA.
kVA
Line-to-line voltage for three-phase, or the single-phase circuit voltage.
V
Nameplate transformer impedance percent.
%
Used to split transformer impedance magnitude into resistance and reactance.
Equivalent downstream resistance in milliohms. Use per-phase equivalent for three-phase, or loop equivalent for single-phase.
mOhm
Equivalent downstream reactance in milliohms. Use per-phase equivalent for three-phase, or loop equivalent for single-phase.
mOhm
Entered equipment interrupting rating or SCCR screen value for utilization comparison.
A

Results

Default result
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Available fault current (I_afc)
1,569 A
Pass

below entered interrupting rating

at entered point

Also computed

Transformer-terminal fault current (I_term) 1,569 A

Infinite-bus transformer current (I_sc) 1,569 A

transformer only, infinite source

Transformer full-load current (I_fl) 90.21 A

Interrupting-rating utilization (U_aic) Pass 7.131 %

Fault apparent power (S_fault) 1,304 kVA

Total Thevenin impedance (Z_total) 0.1766 ohm

Method notes 3 notes
  • Three-phase current uses line-to-line voltage and sqrt(3); downstream R/X should be per-phase equivalent impedance.
  • Infinite-bus mode ignores upstream source impedance and is a conservative transformer-secondary screening assumption.
  • This is an available-fault-current worksheet only. Final interrupting rating, SCCR, current-limiting, arc-flash, OCPD selection and code/AHJ review require detailed system and equipment data.

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