Three Phase Short Circuit Calculation

Short Circuit Current Formula:

\[ I_{sc} = \frac{V}{\sqrt{3} \times Z} \]

Short Circuit Current (I_sc):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is Three Phase Short Circuit Calculation?

Definition: This calculator determines the prospective short-circuit current in a three-phase electrical system.

Purpose: It helps electrical engineers and technicians assess the maximum current that would flow during a fault condition.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ I_{sc} = \frac{V}{\sqrt{3} \times Z} \]

Where:

\( I_{sc} \) — Short circuit current (amperes, A)
\( V \) — System voltage (volts, V)
\( Z \) — Total impedance (ohms, Ω)
\( \sqrt{3} \) — Factor for three-phase systems (≈1.732)

Explanation: The formula calculates the maximum current that would flow if a solid short circuit (zero impedance) occurs between all three phases.

3. Importance of Short Circuit Calculation

Details: Proper short circuit analysis ensures protective devices are correctly sized, prevents equipment damage, and maintains system safety.

4. Using the Calculator

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

5. Frequently Asked Questions (FAQ)

Q1: What voltage should I use?
A: Use the nominal line-to-line voltage of your system (e.g., 480V for commercial systems, 208V for some residential).

Q2: How do I determine the impedance (Z)?
A: Z includes source impedance, transformer impedance, and cable impedance. It's typically calculated from system data or measured.

Q3: Is this for bolted faults only?
A: Yes, this calculates the maximum possible current for a solid (bolted) three-phase fault.

Q4: Does this account for motor contribution?
A: No, this is the basic calculation. Motor contribution would increase the short circuit current.

Q5: What about single-phase systems?
A: For single-phase, use I_sc = V / Z (without the √3 factor).