Short Circuit Current Calculator

Calculate available short circuit current at the transformer secondary and at the end of a conductor run. Required for selecting properly rated breakers, fuses, and equipment.

Safety note: Overcurrent protective devices must have an interrupting rating equal to or greater than the available fault current at their location (NEC 110.9). Undersized OCPD can fail catastrophically during a fault.
Transformer
Conductor to panel (optional)

Please check your inputs.

At transformer secondary
0
amps
At panel / end of run
–
amps
Fault current reduction along conductor
Transformer secondary
0A
At panel
0A
Transformer kVA
Secondary voltage
Full load amps (FLA)
Transformer impedance
Transformer Zt (ohms)
Conductor Zc (ohms)
Fault current reduction
Minimum OCPD interrupting ratings required
Standard OCPD interrupting ratings
Standard breaker (120-240V)10,000A (10 kAIC)
Standard breaker (480V)14,000A (14 kAIC)
High interrupt breaker22,000A (22 kAIC)
Current limiting fuse (Class RK1)200,000A (200 kAIC)
Current limiting fuse (Class L)300,000A (300 kAIC)
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.