What is locked rotor current?

Answer 1

"Locked Rotor Current" also called LRA which stands for Locked Rotor Amps, is commonly found on electric motor nameplates. Locked Rotor essentially means the motor is not turning. The current or amps in this case have to do with the amount of electrical energy required to start the motor. At the instant the motor is switched on, it is not turning, and draws the maximum current. As the motor starts to turn, the current goes down. This required energy is much greater than the Full Load Amps or Running Amps, which is the current drawn when the motor is running at normal speed under full load. The current required to start the motor will depend on the type of motor as well as the specified design voltage required for the motor, typically the higher the voltage, the lower the required amperage or current.

The term also applies to equipment such as Air Conditioners which have an enclosed motor inside the compressor, as well as the condenser fan(s) etc.

Depending on the type of motor, LR current can be anywhere from 3 to 8 times the normal running current, also called RLA, or running load amps.

Answer 2

The maximum torque a specific motor can produce and the maximum current measured in amperes a motor should draw under full load.

Answer 3

In order to calculate locked rotor current, you must consult the data plate from the specific manufacturer. There is no specific formula for this value.