What Is a Reduced Voltage Soft Starter and When Should You Use One?

Industrial motors can draw a significant amount of current the moment they start. That sudden electrical and mechanical force can contribute to voltage drops, equipment stress, and unnecessary wear. A reduced voltage soft starter offers a controlled way to bring an AC motor up to speed by gradually increasing the voltage supplied during startup.

For applications that run primarily at full speed but benefit from smoother starting and stopping, an RVSS can provide an effective middle ground between a traditional across-the-line starter and a variable frequency drive (VFD).

How Does a Reduced Voltage Soft Starter Work?

A reduced voltage soft starter, often called an RVSS or simply a soft starter, uses solid-state components such as silicon-controlled rectifiers (SCRs) to manage the voltage delivered to a motor as it starts. Instead of applying full line voltage immediately, the starter gradually ramps voltage upward until the motor reaches operating speed.

Because motor torque is affected by applied voltage, reducing voltage during startup also reduces starting torque. This creates smoother acceleration and can limit the mechanical shock associated with an abrupt start.

Many modern soft starters also use a bypass contactor. Once the motor reaches full speed, the bypass allows current to flow without continuously passing through the starter’s power electronics, helping reduce heat during normal operation.

What Are the Benefits of a Reduced Voltage Soft Starter?

The primary advantage is controlled motor startup. Depending on the application and equipment selected, an RVSS can help:

Limit high inrush current during startup Reduce voltage disturbances on the electrical system Minimize sudden torque and mechanical stress Reduce wear on belts, couplings, bearings, and driven components Provide smoother stopping where soft-stop functionality is available Reduce pressure surges or water hammer in some pump applications

These benefits make soft starters useful where the motor does not need continuous speed regulation but a full-voltage start creates unnecessary stress.

Reduced Voltage Soft Starter vs. VFD: What Is the Difference?

A reduced voltage soft starter and a VFD can both provide a controlled motor start, but they serve different purposes.

An RVSS primarily controls voltage during starting and, in some applications, stopping. Once the motor reaches full speed, the soft starter generally does not regulate its operating speed.

A VFD controls both voltage and frequency, allowing motor speed to be adjusted while it is running. That makes a VFD better suited for applications requiring variable speed, process control, or specific torque characteristics throughout operation.

If an application only needs a gentler startup while the motor operates at full speed afterward, an RVSS may be the more straightforward solution. If ongoing speed control is necessary, a VFD may be the better fit.

Where Are Reduced Voltage Soft Starters Commonly Used?

Soft starters can be applied to many motor-driven systems, but load characteristics matter. Common applications include pumps, fans, blowers, compressors, and certain conveyors.

Before selecting a reduced voltage soft starter, consider motor horsepower, voltage, full-load current, required starting torque, acceleration time, start frequency, environmental conditions, and load requirements. If available starting torque is reduced too far, the motor may not accelerate the load properly.

How Does Palmer DCS Support Motor Control Applications?

Selecting the right starter is only one part of creating a dependable control system. It must also be properly integrated with circuit protection, controls, enclosures, PLCs, relays, and other components required by the application.

Palmer DCS brings more than 50 years of experience to custom industrial control panels, OEM panels, motor starters, and system integration. The team reviews project requirements and builds electrical control solutions around the equipment and operating environment.

If you're evaluating whether an RVSS, magnetic starter, VFD, or custom motor control panel is right for your system, Palmer DCS can help develop a solution that supports reliable motor control from startup forward.