What is the purpose of a soft starter or VFD in motor control?

• A. To increase starting current quickly.
• B. To accelerate to full speed immediately.
• C. To ramp starting current and speed to reduce electrical and mechanical stress.
• D. To stop the motor during start.

Answer: (C)

Starting a motor puts a big surge of current into the windings and a sudden torque on the mechanical system. A soft starter or a variable‑frequency drive smooths that transition by gradually increasing the voltage (soft starter) or both voltage and frequency (VFD) according to a programmed ramp. This limits inrush current, reduces voltage dips in the electrical supply, and minimizes torque shocks on gears, belts, and bearings, allowing a controlled, gentler acceleration to the desired speed. That’s why this option is the best fit: it describes ramping both current and speed to cut electrical and mechanical stress. It isn’t about forcing a higher starting current, achieving full speed instantly, or stopping the motor during start.