Short Circuit Calculator per IEC 60909-0 for Industrial Installations
IEC 60909-0:2016 + AMD1:2020 provides the standard method for calculating short circuit currents in three-phase AC systems. The voltage factor c (Table 1) accounts for pre-fault voltage variation. For industrial installations, network feeders (Clause 4.3.1), power station units, and motor contributions (Clause 4.5) must be superimposed to determine maximum and minimum fault currents for equipment rating and protection coordination.
Quick Reference Table
| IEC 60909-0:2016 Key References for Industrial Short Circuit — IEC 60909-0 (2016 + AMD1:2020) | ||
|---|---|---|
| Parameter | Value / Requirement | Clause Reference |
| Voltage Factor c | cmax = 1.10 (LV), 1.10 (MV/HV) for maximum fault current | Clause 4.2 / Table 1 |
| Network Feeder Impedance | Calculated from system fault level at point of common coupling | Clause 4.3.1 |
| Motor Contribution | Asynchronous motors contribute decaying fault current based on I_LR/I_rM ratio | Clause 4.5 |
| Peak Short Circuit Current | ip = κ × √2 × I"k — κ factor depends on R/X ratio per Clause 4.3.1.2 | Clause 4.3.1.2 |
| Generator Contribution | Synchronous generators modeled with subtransient reactance X"d | Clause 4.6 |
| Minimum Short Circuit Current | Uses cmin factor and maximum impedance for protection sensitivity checks | Table 1 (cmin column) |
How to Calculate Short Circuit for Industrial Installations
- 1
Define the system topology and fault location
Draw the single-line diagram showing all sources (utility, generators, motors) and impedance elements (transformers, cables, busbars) between sources and the fault point.
- 2
Refer impedances to the fault voltage level
Convert all source and element impedances to the common voltage base at the fault location using IEC 60909-0 impedance correction factors for transformers (Clause 4.3.2) and generators (Clause 4.6).
- 3
Calculate initial symmetrical short circuit current I"k
Apply the voltage factor cmax from Table 1 and compute I"k = (c × Un) / (√3 × |Zk|), where Zk is the total equivalent impedance at the fault point.
- 4
Determine peak current ip and breaking current Ib
Calculate the peak short circuit current using the κ factor (Clause 4.3.1.2) based on the R/X ratio. Determine the symmetrical breaking current accounting for AC and DC decay.
- 5
Add motor contributions
Include asynchronous motor fault contributions per Clause 4.5. Motors above the threshold (typically Σ motor ratings > 1% of I"k) must be included with their subtransient impedance.
- 6
Verify equipment ratings against calculated fault currents
Compare the maximum I"k with switchgear breaking capacity, ip with peak withstand ratings, and the thermal equivalent current with short-time withstand (Icw) ratings of all equipment in the fault path.
Try the Short Circuit Calculator
Run compliant IEC 60909-0 calculations for industrial installations — free, instant results with full clause references.
Calculate Short Circuit NowAC vs DC Fault Current Comparison
| Parameter | AC Fault | DC Fault |
|---|---|---|
| Natural zero crossing | Yes (every half cycle) | No natural zero crossing |
| Arc extinction | Easier (current passes through zero) | Harder (sustained arc) |
| Calculation standard | IEC 60909-0 | IEC 61660-1 |
| Peak factor | 1.02–1.8 (depends on X/R ratio) | 1.0 (no AC component) |
| Protection challenge | Well-established CB technology | Requires specialised DC breakers |