1. What is Inrush Current?

Inrush current is the instantaneous high input current drawn by electrical devices when first turned on. This transient current can be much higher than the steady-state current and is an important consideration in circuit design.

2. How Does the Calculator Work?

The calculator uses the inrush current formula:

Where:

• \( Multiplier \) — Dimensionless factor (typically 5-100x for motors, 10-100x for transformers)
• \( Steady\ State\ Current \) — Normal operating current in amperes (A)

Explanation: The multiplier accounts for the initial surge of current required to overcome inertia in motors or to establish magnetic fields in transformers.

3. Importance of Inrush Current Calculation

Details: Calculating inrush current is crucial for proper sizing of circuit protection devices, preventing nuisance tripping, and ensuring reliable operation of electrical systems.

4. Using the Calculator

Tips: Enter the multiplier (typically provided in equipment specifications) and the steady-state current in amperes. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What are typical multiplier values?
A: Small motors: 5-10x, large motors: 5-8x, transformers: 10-40x, switching power supplies: 20-100x.

Q2: How long does inrush current last?
A: Typically 1-30 cycles (16-500ms at 60Hz), depending on the equipment and circuit characteristics.

Q3: What problems can inrush current cause?
A: Voltage sags, nuisance breaker tripping, contact welding, and premature component failure.

Q4: How can inrush current be limited?
A: Using soft starters, current-limiting resistors, NTC thermistors, or phase-controlled switching.

Q5: Is inrush current the same as starting current?
A: For motors, starting current includes both inrush and the current needed to accelerate the load to operating speed.