Short Circuit Current Calculator

What is Short Circuit Current?

A short circuit is an unintended low-resistance path that allows a large current to flow. The prospective short circuit current (PSCC) is the maximum current that could flow at a fault point. Protection devices (fuses, MCBs, MCCBs) must have a breaking capacity greater than the PSCC.

The Formula

Single phase: Isc = V / Z Three phase: Isc = V_line / (√3 × Z)

Where Z is the total system impedance at the fault point, including: source (transformer/grid) impedance + cable impedance.

How to Use This Calculator

Enter system voltage, system type (single/three phase), and total impedance. The calculator returns Isc and helps you verify that your protection devices are adequately rated.

Practical Examples

Example 1: 230V single phase, Z = 0.05Ω. Isc = 230 / 0.05 = 4,600A = 4.6kA. MCB must have 6kA breaking capacity (standard domestic MCBs are rated 6kA).

Example 2: 415V three phase, Z = 0.1Ω. Isc = 415 / (√3 × 0.1) = 415 / 0.173 = 2,398A ≈ 2.4kA.

Why This Matters

If a protection device's breaking capacity is lower than Isc, it can explode or weld shut during a fault, causing fire and electrocution hazards. Always verify breaking capacity against calculated PSCC during circuit design.