Inrush Current

Ametherm’s Inrush Current Limiters

Looking for Data Sheets?

UL & CSA Approved Inrush Current Limiter Data Sheets

All Inrush Current Limiters


About Inrush Current Limiters

Inrush current limiters (ICLs) are components used to limit the surge of current that occurs when an electrical device is first turned on. This surge of current, also known as inrush current, can be very high, and it can damage the device or the power supply. ICLs work by increasing the resistance of the circuit when there is a high current. This reduces the current flow and protects the device.

ICLs are often used in power supplies, motors, and other devices that have a high inrush current. They are an important safety feature for many electrical devices, as they help to protect the devices from damage and to prevent power surges.

Here are some of the benefits of using inrush current limiters:

  • They protect devices from damage caused by inrush current.
  • They prevent power surges.
  • They can improve the efficiency of power supplies.
  • They are relatively inexpensive.

If you are designing an electrical device that has a high inrush current, you should consider using an inrush current limiter. They are a simple and effective way to protect your device from damage.

Standard Surge Limiter

Standard Surge Limiter

The Standard Surge Limiter Series feature devices designed to safeguard electrical systems from damaging power surges. These surge limiters are UL Rated for their safety and performance. With inrush current protection capabilities of up to 90 Joules of energy and 10 Amps of current, they provide robust defense against sudden voltage spikes.

These Inrush Current Limiters can be used in Residential, Commercial, Industrial, Healthcare, Renewable Energy, and Electric Vehicle Applications.

MS35 Series

MS35 Series

The MS35 Series of inrush current limiters exhibit an impressive capability to manage up to 800 Joules of energy and steady-state currents ranging from 10 A to 50 A. These power thermistors are designed with durability in mind, ensuring long-lasting performance even in the most challenging high-power scenarios.

In alternative and green energy applications, the MS35 Series assumes a crucial role by mitigating current spikes that can occur during the transfer of power from sources like wind turbines and solar panels. By effectively controlling the flow of energy into batteries, inverters, and other energy storage components, these limiters help maintain stability and reliability within the system.

AS Series

AS Series

The AS Series is designed to protect electronic components, including power supplies, transformers, rectifiers, pre-charge circuits, and more, from inrush currents. These UL-rated Inrush Current Limiters provide protection ranging from 230 to 1000 Joules and can withstand current levels of 10 to 50 Amps.

They ensure component safety and extend operational lifespan. With their compact design, the AS Series offers a cost-effective solution for inrush current mitigation. These ICLs are highly durable and suitable for various applications. Ametherm’s AS Series is a reliable choice for engineers and designers seeking efficient inrush current limiting solutions.

MegaSurge Banner
Mega Surge Inrush Current Limiters

MegaSurge Series

The MegaSurge Series of inrush current limiting NTC thermistors offer a simple and cost-effective alternative to using wirewound resistors in combination with timers and relays. These thermistors not only reduce costs but also simplify designs significantly. Moreover, they enhance safety by eliminating the fire hazard associated with failed relays.

Unlike traditional thermistors that are certified for input voltages ranging from 85 VAC to 265 VAC, the UL-recognized MegaSurge devices are certified for both single- and three-phase input voltages up to 480 VAC. This expanded voltage certification provides greater flexibility in application.

In terms of performance, MegaSurge devices have exceptional capabilities. They can withstand high steady-state currents of up to 36 A and handle input energy of up to 300 J. These specifications represent the highest among any single-solution inrush current limiting device available in the market.

The MegaSurge series targets a wide range of applications, including the inrush current protection of power supplies, motor controllers, audio amplifiers, battery chargers, frequency generators, plasma cutting tools, MRI machines, and toroidal transformers. These thermistors offer reliable and efficient inrush current limiting for various electronic systems.

MCL20 500100 PTC Inrush Current Limiter

Inrush PTC Thermistor

The MCL20 500100-A stands out with its remarkable voltage rating, enabling it to withstand numerous instances of maximum inrush current without degradation.

One of the device’s key advantages is its short reset time. As a PTC thermistor, it experiences a quick reset without generating a large inrush current due to its already high resistance state. This characteristic enhances reliability and stability in high-voltage applications.

The MCL20 500100-A offers designers a more compact and cost-effective solution, measuring 19 mm in diameter, with a maximum profile of 9 mm and a lead spacing of 7.8 mm. This eliminates the need to combine a power resistor, relay, and timer on a single circuit to achieve the same functionality.

This thermistor is specifically designed for applications requiring inrush current limiting and overcurrent protection in high-voltage scenarios, such as welding equipment and plasma cutters operating in the range of 480 V to 930 V.

MM35-DIN in a DIN Block


The MM35-DIN Series is specifically designed to handle high power industrial applications, offering continuous current ratings from 50A to 80A at 680V RMS and energy up to 1,200 joules. These Inrush Current Limiters can effectively manage the high power levels found in industrial environments.

The MM35-DIN Series provides higher energy ratings and is ideal for power distribution purposes. With higher continuous current ratings, these limiters are well-suited for systems that are typically powered on once daily. They offer a single part solution, eliminating the need for additional bypass circuitry.

These limiters can be used in both single and three-phase applications, including AC motors, transformers, power supplies/inverters, and more. The Maximum Power Ratings Chart provides further application guidance. Mounting the MM35-DIN Inrush Current Limiters is a straightforward process, as they are designed for use with DIN blocks, requiring only a screwdriver for installation in a power control box.

Whether dealing with three-phase or single-phase power, the MM35-DIN Series of Inrush Current Limiters is the optimal choice for high power application requirements in industrial settings.

MiniAmp Banner
MiniAmp Inrush Current Limiter

MiniAmp Series

The miniAMP series offers miniature inrush current limiters designed for space-sensitive applications. These compact devices are ideal for situations where board space is limited and cool operation is desired. The cost-effective miniAMP inrush current limiter efficiently protects components like relays, diodes, and fuses from inrush current.

Available in 3, 5, and 8mm diameters, these lightweight limiters weigh as little as 0.06 grams. The miniAMP series features cold resistance ranging from 5 ohms to 220 ohms.

With a continuous current rating of 250 mA to 3 Amperes and up to 20 joules of input energy, this inrush current limiter series delivers reliable performance. It operates within a temperature range of -40 to +150 degrees C.

The radial leaded miniAMP inrush current limiters are available with kinked or straight leads, with a standard lead length of 1/2 inch. They come packaged in bulk and are also available on Tape and Reel for convenience.

RTI Logo
RTI SURGE-GARD Inrush Current Limiters

RTI SURGE-GARD™ Inrush Current Limiters

RTI’s SURGE-GARD™ Inrush current limiting devices, made from specially formulated metal oxide ceramic materials, effectively suppress high inrush current surges.

The recovery time for SURGE-GARD™ devices varies based on factors such as the device itself, mounting configuration, and ambient temperature. A minimum cool down time of 60 seconds is recommended. These devices offer features such as the reduction of required peak forward surge current rating, noise reduction, and prevention of fuse failures.

RTI’s SURGE-GARD™ Inrush current limiting devices offer the following installation options:

  • Thru-hole leads
  • Insulated/uninsulated configurations
  • Standoffs
  • Preformed leads

It is important to note that SURGE-GARD™ devices should not be used in parallel, as one unit would bear the majority of the current. These devices provide reliable protection and can be easily integrated into various power supply applications.

BigAMP Surge Limiter Banner
BigAmp Inrush Current Limiters

bigAMP Series

The bigAMP Series effectively handles high inrush current during power-on events by providing a high resistance initially and rapidly decreasing its resistance once steady state current flows through the thermistor.

In switching power supplies, the surge energy occurs due to large input filter capacitors and AC input voltage. During energy absorption, the thermistor’s high resistance swiftly drops to a negligible level within milliseconds, enabling the smooth flow of steady state current with minimal power loss in the circuit.

The bigAMP Inrush Current Limiter can absorb up to 260 joules of input energy and sustain 36 amperes of steady state current. It finds utility in various applications, including switching power supplies, AC motors, uninterruptible power supplies, variable frequency drives, and any equipment that can benefit from inrush current protection.

Ametherm’s bigAMP Inrush Current Limiters are purposefully designed thermistors capable of withstanding continuous current up to 36 amperes and input energy up to 260 joules.