Short Circuit Current Calculator
Calculate available fault current, X/R ratio, and interrupting duty at a point downstream of a transformer.
Inputs
kVA
%Z
V
m
mm²
phase
Results
Available Fault Current
14,648 A
Min. Withstand Rating
15,000 A
X/R Ratio0.91
Interrupting Duty14,648 A
How to Use This Calculator
- Enter the Transformer KVA rating and its Percent Impedance (%Z) from the transformer nameplate — typical 5–6% for 1,000+ kVA units.
- Enter the Secondary System Voltage in volts (e.g., 208 or 480 V).
- Enter the Cable Length in meters from the transformer to the fault point and the Cable Size in mm².
- Select the Number of Phases (1 or 3).
- Read the Available Fault Current in amperes — use this to verify breaker and switchgear interrupting ratings.
- Use the Minimum Withstand Rating in amperes to confirm buses, lugs, and equipment can survive a bolted fault without damage.
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