What is the typical factor for the locked-motor current when a motor is first connected to the power source?

The typical factor for the locked-motor current, which is the current drawn by an electric motor when it is first connected to the power source and not yet rotating, is generally in the range of 2 to 3 times the motor's full-load current. This phenomenon occurs due to the initial inrush of current required to overcome the inertia of the motor rotor and to establish electromagnetic fields within the motor.

When a motor starts, it faces significant resistance and lacks rotational motion, leading to a high current draw as it attempts to reach its operational speed. The locked-motor current is much higher than the running current because, at startup, the motor is still stationary, and it's drawing maximum current to initiate movement. The figure of 2 to 3 times reflects standard practices observed in various motor types, particularly in induction motors, which are commonly used in water distribution systems.

Understanding this factor is crucial for designing electrical systems and ensuring that circuit protection devices can handle the inrush current without tripping, thus preventing unnecessary downtime in water distribution operations.