Short-Circuit Current

What is this formula?

This formula calculates the prospective short-circuit current available at a point in an electrical system by dividing the system voltage by the equivalent impedance seen from the fault location.

When to use it

Use this formula during fault studies, protection system design, circuit breaker selection, switchgear rating verification, and electrical safety analysis.

Example

A power system has:

Voltage = 480 V

Equivalent impedance = 0.08 Ω

Formula:

Isc = V / Z

Substitution:

Isc = 480 / 0.08

Result:

Isc = 6,000 A

Isc = 6.0 kA

Applications

Short-circuit studies

Circuit breaker sizing

Protective device coordination

Switchgear rating verification

Electrical safety assessments

Note

This equation represents the basic theoretical relationship between voltage, impedance, and fault current. Real power systems may require more detailed models that include transformer impedance, generator contributions, motor contributions, X/R ratio effects, and symmetrical versus asymmetrical fault currents.