Motors play an important part in the modern domestic and industrial environment, and should therefore be of interest to the electrician. It may be divided into two distinct kinds: those using direct current (d.c.) and those using alternating current (a.c.). In practice, the d.c. motor comprises an armature of many loops revolving between electromagnetic poles. The series motor is best used where heavy masses need to be accelerated from rest, such as in cranes and lifts. If by some means a d.c. motor is supplied with motive power it will act as a generator. There are many different types of a.c. motor operating from either three-phase or single-phase a.c. supplies. A three-phase motor depends on the rotation of a magnetic field for its movement. Once the most appropriate type of motor for a particular task has been selected, it is necessary to ensure that the motor enclosure is also suitable for its working environment.