A wound rotor induction motor differs from a squirrel cage induction motor only in the construction of its rotor. The rotor, instead of having short-circuited copper bars, has a definite winding connected for the same number of poles as the stator with the leads brought out to slip rings. The stator and rotor are commonly called the primary and secondary, respectively, because under locked rotor conditions, the motor becomes a transformer with a given ratio. This ratio depends upon motor design and is not standardized. Frequently called a slip ring motor.