Short-Circuit Fault Current Calculator
How much fault current will actually flow? Calculated by BOTH standards — IEC 60909-0 and ANSI/IEEE C37 — with the one your country uses picked automatically, and the other available side by side when you need to compare.
The system
Auto picks the one your country uses
The secondary side, line to line
V
From the network operator. Leave at 0 for an infinite source.
MVA
Advanced / Custom Input — the source
Primary side, used to refer the source impedance across.
V
Filled in from the voltage. IEC only — ANSI has no equivalent.
Hz
The transformer
From the nameplate
kVA
The uk% figure on the nameplate
%
Advanced / Custom Input — the transformer
IEC only. ANSI uses nameplate impedance as it is.
Nameplate impedance is usually ±10%. A LOWER impedance gives a HIGHER fault current, so use −10% for the worst case.
%
The cable run
Pick “both” for a proper distribution study
m
Two cables in parallel halve the impedance
nos
Advanced / Custom Input — the cable
Filled in from the size. Copper, at operating temperature.
Ω/km
Ω/km
The protective device
The Icu or Icn figure on the device. Leave at 0 to skip the check.
kA
Advanced / Custom Input — the device check
Checked against the peak current, not the RMS. Leave at 0 to skip.
kA
The tool checks the MINIMUM fault current clears this.
kA
IEC uses a lower c when checking that protection will actually see the fault.
Result
Put in your source, transformer and cable, then press “Calculate the fault current”.
Estimate only — verify with a licensed electrical engineer and a full protection study before selecting or rating equipment.