How To Select an Inrush Current Limiter

Ametherm’s inrush current limiters are designed to protect your components from damaging levels of inrush current at startup.
Inrush Current Limiters

Online Calculators




Inrush Current Limiters CSA approvalUL rated

Rated to 50 Amperes and 900 Joules of input energy. For Motor Drives, Audio Equipment, and Power Supplies
Rated up to 36 amperes and 260 joules of input energy. For UPSs, Motor Controls, and Power Supplies with 750 watts or higher output.
Specially designed for value. Available in 3, 5, and 8mm diameters and weigh as little as 0.225 grams
Large variety of the sizes and electrical specifications of the most common inrush current limiters.

Inrush Current Application Notes

Inrush Current Limiters
Power Electronics article discusses applications and uses of inrush current limiting thermistors
Inrush Current FAQ
Frequently Asked Questions about inrush current limiting thermistors
Inrush Current in Transformers
A sample application of inrush current limiters
in transformers
Inrush Current Causes and Prevention
A summary of inrush current causes and prevention
Ametherm Imax Derating Curve
Ametherm Derating Curve
Ametherm Zero Power Resistance Curve
Ametherm Zero Power Resistance Curve

Inrush Energy Calculator

Inrush Energy (J)How To select an Inrush Current Limiter

Joules Calculator

Voltage (Vpeak)
Capacitance (µF)
Total Energy (J)
  1. Use the maximum allowable surge current and Ohm’s Law to determine the least allowable resistance at turn on for your application.
  2. Using the formula J = .5CV^2, determine how much input energy the thermistor will absorb when the device is turned on.
  3. Determine the maximum steady state current that will flow through the Inrush Current Limiter.
  4. Select the Inrush Current Limiter that will work for your application.Power Thermistor Selection Calculator