Short-Circuit Current Calculator
An engineering calculator for computing short-circuit currents in low-voltage 0.4 kV networks. Calculates steady-state three-phase short-circuit current, peak (making) current, and single-phase short-circuit current for protective device sensitivity verification.
Calculations follow GOST 28249-93 and IEC 60909 methodology. Parameters considered include supply transformer characteristics (power, short-circuit voltage), cable line impedance, contact transition resistances, and arc resistance.
Features
- Three-phase short-circuit current calculation (Ik3)
- Single-phase short-circuit current calculation (Ik1) — phase-to-neutral loop
- Peak short-circuit current calculation (ip)
- Transformer parameter consideration
- Cable line impedance consideration (resistance + reactance)
- Circuit breaker sensitivity verification
- Comparison with device breaking capacity ratings
Standards
- IEC 60909-0 — Short-circuit currents in three-phase AC systems
- GOST 28249-93 — Short circuits in electrical installations up to 1 kV
- PUE (Russia) — Electrical Installation Code
Frequently asked questions
What is the SC power at the input?
Sк — the short-circuit power at the service point (typically 6–20 MVA from a distribution transformer). Higher Sк means higher fault current.
Why check a 6 kA breaker?
The breaking capacity must not be lower than the fault current at that point. If the fault current exceeds 6 kA, use a 10 kA breaker.
Why does fault current drop along the line?
Cable resistance grows with length: R = ρ·2·L/S. At the end of a long run the fault current can be tens of times lower.
What fault current is in a socket outlet?
With Sк = 10 MVA and a 30 m run of 2.5 mm², the fault current ≈ 500 A — enough to trip the breaker and below 6 kA.