What is a soft-start device and why is it used?

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Soft-starts control how fast a motor reaches full speed by ramping the applied voltage (and sometimes frequency) from zero up to full value. This gradual ramp reduces the inrush current that occurs when a motor starts from rest, which is a large surge because the windings look almost like a short circuit. Lower inrush keeps voltage dips from affecting the rest of the electrical system, provides smoother acceleration, and reduces mechanical shocks to the motor and connected hardware like belts, gears, and couplings. It also helps protect components such as contactors and fuses from sudden full-load surges. This isn’t about storing energy for peak demand, nor about cooling the motor, and it doesn’t apply full voltage instantly—that would defeat the purpose of soft-starting. Different implementations include autotransformer starters, solid-state soft starters, and variable-frequency drives.