Variables
Description
What is this formula?
The fault current equation calculates the current that flows during an electrical fault based on the system voltage and the impedance of the fault path.
When to use it
Use this formula when performing protection studies, selecting circuit breakers, evaluating equipment ratings, and analyzing electrical system safety.
Example
A fault occurs on a system with:
Voltage = 13,800 V
Fault impedance = 0.5 Ω
Formula:
If = V / Zf
Substitution:
If = 13800 / 0.5
Result:
If = 27,600 A
If = 27.6 kA
Applications
Protection system design
Circuit breaker selection
Switchgear rating verification
Electrical safety studies
Short-circuit analysis
Note
This equation provides the basic relationship between fault current, voltage, and fault impedance. Real fault studies often include source impedance, transformer impedance, conductor impedance, motor contributions, and asymmetrical fault effects. Therefore, actual fault currents may differ from this simplified calculation.