EngineerHub.orgDrawing No. EH–EE–012 // Electrical Engineering
IEC 60909 Short-Circuit Calculator
Reviewed August 2026
Build a transparent radial equivalent from source to fault and calculate I″k, ip, Ith, Sk″, κ and the key IEC correction factors.
01 // IEC 60909 network
Upstream source
Enter the upstream source short-circuit power applicable to the selected maximum/minimum case. If the utility or network study provides different source strengths for the two cases, change this input when switching case; the voltage-factor selector alone does not create a second source-strength dataset.
Transformer
Line / cable to fault
Fault & current-source contributions
02 // Short-circuit results
This model uses the equivalent-voltage-source method at the fault location. It builds the positive-sequence source + transformer + line equivalent, applies fault impedance in the appropriate fault loop, applies the transformer correction KT, calculates I″k, κ and peak current, and offers manual zero-sequence entry for a single-phase-to-earth fault.
It is intentionally a transparent single-path network calculator rather than a full nodal short-circuit program. Generator decrement, complex meshed-network κ methods, detailed inverter models and provisions from later standard revisions still require specialist software or a full standard calculation.
Background & method
IEC 60909-0:2016, Edition 2.0, is the current, in-force edition for short-circuit-current calculation in LV and HV three-phase AC systems at 50 or 60 Hz. This page focuses on a transparent equivalent-voltage-source calculation that can be audited by hand.
FAQ
IEC 60909-0:2016, Edition 2.0 ("Short-circuit currents in three-phase a.c. systems – Part 0: Calculation of currents"), which is the current, in-force edition. A third edition has been under development at IEC but had not entered into force as of this page's last review. The page implements a transparent subset of the standard method rather than claiming full software compliance.
IEC short-circuit calculations use an equivalent voltage source c·Un at the fault to represent operating-voltage deviations. Maximum and minimum cases use different factors.
The first current peak includes the decaying dc offset. IEC uses a peak factor κ based on the equivalent R/X ratio; for a radial equivalent, κ = 1.02 + 0.98e^(−3R/X).
The standard applies a transformer impedance correction factor. The calculator uses KT = 0.95·cmax/(1 + 0.6xT) for the included two-winding transformer equivalent.
No. It is designed to make the IEC calculation transparent and useful for hand-checking. Large meshed systems, generator decrement, protection coordination and detailed converter models need a network solution.