Engineering CalculationShort-circuit Current Calculator - Fault Level at a Board
Work out the prospective fault current at any LT board so that breakers, busbars and cables are rated for it.
Open the calculator →Formula
At transformer LV terminals: ISC = IFL × 100 / Z%
At a downstream board: ISC = V / (√3 × Ztotal), Ztotal = source + transformer + cable impedance
Worked example
2000 kVA, 433 V, impedance 6.25 %, infinite source
IFL = 2,667 A; ISC = 2,667 × 100 / 6.25 = 42.7 kA
Where engineers use it
- Breaker breaking-capacity (Icu / Ics) selection
- Panel and busbar kA rating
- Cable short-circuit withstand check
How to use
- Click Open the calculator. It runs free in your browser, on desktop or phone.
- Enter your values. Units and typical ranges are shown next to each input.
- Read the result and the step-by-step working, then print or add it to your Project BOQ.
Questions
Is this the same as arc flash?
No. Arc flash incident energy is a separate calculator (IEEE 1584-2018) in the Electrical suite.