Short-circuit current
Estimate the initial symmetrical fault current at transformer terminals from its rating and impedance.
Enable JavaScript for live calculations. Read the method and default example below.
Method and assumptions
- Isc ≈ rated current × 100 / impedance (%).
- Assumes an infinite upstream source at nominal voltage. Feeder impedance, motor contribution, tolerances and voltage factors are not included.
Before using the result
- This approximation is not a full IEC 60909 study. It does not calculate peak current, downstream fault level or certify switchgear breaking capacity. Obtain utility and manufacturer data for the final study.
Worked example
Illustrative default inputs. Enter your project values above.
- Transformer rating
- 1000 kVA
- Nameplate impedance
- 5 %
- Supply voltage
- 415 V
- Supply arrangement
- Three phase — balanced
Default results
- Transformer rated current
- 1,391.2 A
- Terminal fault estimate
- 27.82 kA
- Calculation location
- Transformer terminals
Choose a reference or send your BOQ
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Technical references
These references support planning. The exact model documentation and a project-specific engineering review govern the final specification.