Drives & Motor Control

Soft Starters

Reduced-voltage starting for AC motors. 10 products from 2 brands.

About soft starters

A soft starter limits the inrush current and torque when an AC induction motor starts. It uses thyristors to ramp up the voltage applied to the motor over a set time, so the motor accelerates smoothly instead of jumping straight to full voltage as it would on a direct-on-line starter. That reduces the voltage dip on the supply, the mechanical shock on couplings, belts and gearboxes, and, on pumps, the pressure surges that cause water hammer. Many soft starters also provide a controlled soft stop and built-in motor protection. Because the motor still runs at full speed once started, a soft starter is a simpler and usually smaller alternative to a variable speed drive where speed control is not needed.

This page lists 10 soft starters from ABB and Schneider Electric, from compact units for small motors to advanced ranges with built-in bypass, protection and communication. Use the brand shortcuts or the filters to narrow the list, open a product for its information sheet, and add the models you need to one quotation request.

All soft starters

10 products

Buying guide

Choosing a soft starter

A soft starter is sized for the motor and for how hard and how often it has to start. These are the points to check before you request a quotation.

01

Motor current and supply

Select the soft starter by the motor's rated current from the nameplate, not only by kilowatts, and confirm the supply voltage and frequency. Check the control supply voltage the unit needs as well.

02

Starting duty

Normal starts, such as centrifugal pumps and fans, need less current for less time than heavy starts, such as loaded conveyors, crushers or high-inertia fans. Heavy starts and frequent starts per hour may require a larger soft starter than the motor rating alone suggests.

03

In-line or inside-delta connection

Most soft starters are connected in line with the motor. Some models can also be connected inside the motor's delta winding, which lets a smaller unit control a larger motor. Inside-delta wiring needs six motor leads and is only possible with soft starters designed for it.

04

Bypass and heat

Once the motor is up to speed, a bypass contactor, often built in, takes over so the thyristors no longer carry the running current. This reduces heat in the panel. Allow for the manufacturer's ambient temperature limits and cooling clearances.

05

Stopping, protection and communication

For pumps, a soft stop or pump-control stop helps reduce water hammer. Check which motor protection functions are built in, such as overload and phase loss, and whether you need fieldbus communication to your control system.

06

Soft starter or variable speed drive?

A soft starter only controls starting and stopping; the motor then runs at full speed. If the process needs to run at different speeds, or you want the energy savings of slowing pumps and fans down, a variable speed drive is the better choice.

Not sure which soft starter fits? Send us the motor nameplate details, the type of load and how often it starts with your quotation request.

Typical applications

  • Centrifugal pumps
  • Fans
  • Conveyors
  • Compressors
  • Crushers
  • Mixers
  • Water and wastewater pumping

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