What is the typical range for locked rotor current of a large induction motor, expressed in terms of rated current?

The typical range for locked rotor current in large induction motors is indeed expressed as a multiple of the rated current, with the correct range being 6 to 8 times the rated current. Locked rotor current refers to the current drawn by the motor when it is started and the rotor is not yet turning, indicating the conditions when the motor experiences its highest electrical demand.

This high current is a critical factor for design and operations, particularly in determining the specifications for electrical components such as circuit protection and wiring. When motors are started, they can draw large amounts of current due to the lack of back electromotive force (back EMF) that normally opposes the supply voltage when running at operational speed.

Understanding this range helps engineers ensure proper selection of motor starters and circuit protections that can handle these high initial currents without tripping. The standard industry practice recognizes that larger motors typically exhibit this higher locked rotor current as a function of their design characteristics and operational needs. Thus, the range of 6 to 8 times rated current appropriately reflects the current scenario for large induction motors during starting conditions.