๐Ÿ’ฅ Fault Current & AIC

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System inputs

Transformer (source)

Feeder cable to panel

Available fault current at panel

Short-circuit current (Isca)
โ€” A
Recommended breaker AIC rating: โ€”
Transformer FLA
โ€” A
At xfmr terminals
โ€” A
f multiplier
โ€”
Cable Z per ft
โ€” mฮฉ/ft

Point-to-point method

Isca(xfmr) = (kVA ร— 1000) / (V ร— โˆš3 ร— %Z รท 100)
f = (โˆš3 ร— L ร— I) / (C ร— V)
Isca(panel) = Isca(xfmr) ร— 1 / (1 + f)
Estimate only. Simplified point-to-point method; conductor C-values from Cooper Bussmann Electrical Plan Review, Table 2 (three single conductors, 600 V). Ignores motor contribution, source impedance from the utility, and the reactance-only impedance in very short runs.
โšก Teaching visualization. Uses the Bussmann/IEEE point-to-point simplification with lookup-based conductor C-values. Real engineering-grade fault-current studies must include utility impedance, motor contribution (typically 4ร— motor FLA within 4 cycles), and reactance-only impedance at very short cable runs. Verify AIC ratings against manufacturer breaker curves and follow CEC Rule 14-012 / NEC 110.9 for interrupting-rating selection.