Free calculator · Transformers
Transformer Fault Current Calculator
Explore the symmetrical three-phase terminal-fault estimate with an infinite primary supply.
Interactive calculator · explicit assumptions
Transformer Fault Current Calculator
Calculations run in your browser. Sharing puts numeric assumptions in the link. No registration required.
Formula
Rated A = kVA × 1,000 ÷ (√3 × VLL). Estimated symmetrical fault kA = rated A ÷ (Z% ÷ 100) ÷ 1,000.
Worked example
1,000 kVA at 480 V with 5.75% impedance gives approximately 20.9 kA under the stated idealized assumption.
What this calculation does not cover
Ignores source and feeder impedance, impedance tolerance, parallel paths and motor contribution. It is not an arc-flash calculation or a final interrupting-duty study.
Sources & further reading
Using the result responsibly
Keep a record of the input units and operating assumptions. A change in one input can make two apparently similar equipment options impossible to compare. Export the scenario before reviewing it with your engineer or equipment manufacturer.
Educational planning only. These tools do not replace a licensed professional’s design, a manufacturer selection study or applicable local requirements.