1. What is Prospective Fault Current Calculation?

Definition: This calculator estimates the prospective short-circuit current in a 3-phase electrical system based on voltage and impedance.

Purpose: It helps electrical engineers and technicians determine potential fault currents for proper protective device selection and system design.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( I_{sc} \) — Prospective short-circuit current (amps)
• \( V \) — System voltage (volts)
• \( Z \) — System impedance (ohms)
• \( \sqrt{3} \) — Constant for 3-phase systems (≈1.732)

Explanation: The voltage is divided by the product of impedance and square root of 3 to calculate the prospective fault current in a balanced 3-phase system.

3. Importance of Fault Current Calculation

Details: Accurate fault current calculation ensures proper sizing of circuit breakers, fuses, and other protective devices to maintain system safety and reliability.

4. Using the Calculator

Tips: Enter the system line-to-line voltage in volts and the total system impedance in ohms. Both values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: Why is √3 used in the formula?
A: The square root of 3 (≈1.732) is a constant that relates line-to-line voltage to phase voltage in balanced 3-phase systems.

Q2: What voltage should I use?
A: Use the nominal line-to-line voltage of your system (e.g., 400V, 480V, etc.).

Q3: How do I determine system impedance?
A: System impedance includes transformer impedance, cable impedance, and other circuit components. It's often provided in equipment specifications.

Q4: Is this calculation for symmetrical or asymmetrical current?
A: This calculates the symmetrical RMS short-circuit current. Asymmetrical current would be higher in the first cycle.

Q5: Does this account for motor contribution?
A: No, this is the basic calculation. Motor contribution would increase the actual fault current.