What do code letters on motor name plates indicate?

Motor nameplates contain important data that describes the operational characteristics of the motor. The code letters found on these nameplates specifically indicate the locked rotor current, which is a critical aspect of motor performance.

Locked rotor current refers to the amount of current that a motor draws when it is trying to start but has not yet begun to turn. This is significantly higher than the current the motor will draw when it is running at normal speed. The letters on the nameplate correspond to established code letters standardized by the National Electrical Manufacturers Association (NEMA), which help in determining the motor's locked rotor current rating. This information is crucial for selecting appropriate circuit protection and ensuring that the electrical supply can handle the inrush current during motor start-up.

Understanding locked rotor current is vital for electricians and engineers because it impacts system design, including the selection of breakers, fuses, and wire sizes to avoid potential overloads and maintain safe operation.