Line impedance starters are used to:

Line impedance starters are designed to limit the starting current of an electric motor. When an electric motor starts, it draws a significantly higher amount of current than when it is running at its rated speed. This high starting current can cause damage to both the motor and the electrical supply system, as well as lead to undesirable effects such as voltage drops.

By incorporating a line impedance starter, resistors or inductive devices are placed in series with the motor during startup. This added impedance restricts the amount of current that can flow into the motor, effectively controlling the inrush current to safer levels. As the motor reaches a certain speed, the impedance can be gradually removed or reduced, allowing the motor to operate efficiently under normal conditions.

This method not only protects the motor and the electrical system but also can mitigate mechanical stresses on the motor components during startup.