Locked rotor current is generally how many times greater than the run current?

Locked rotor current is typically the maximum electrical current drawn by an electric motor during the start-up phase when the rotor is not yet turning. This high current occurs because the motor windings present a low resistance until the rotor reaches its operational speed.

When considering the relationship between locked rotor current and run current, it is widely accepted that the locked rotor current can be approximately 4 to 6 times greater than the normal running current. This significant increase in current ensures that the motor has enough torque to overcome inertia and start rotating effectively. Once the motor is up to speed, the current will decrease to the normal operating or run current, which is much lower due to the reduced impedance in the windings when the rotor is in motion.

The choice indicating that the locked rotor current is 4-6 times greater accurately reflects standard industry practices and provides a realistic expectation for technicians working with electric motors in HVAC systems. Understanding this concept is essential for HVAC professionals, as it helps in troubleshooting and properly sizing electrical components such as circuit breakers and contactors, preventing potential damage to the motor and improving system reliability.