The work of the electric railway requires a special type of motor of great flexibility. For example, the current demanded by a motor in starting a car is always in excess of the current afterwards required to run the car at full speed on a level track. The rating of a railway motor is the horse-power output it will deliver during a one-hour run at a rated voltage at the brushes with a temperature rise of any part of the motor not exceeding 70° C. A car motor usually has its four poles covered so as to be waterproof. It transmits power by means of a single reduction gear. The motor is suspended at one end upon the car axle, and the spring is suspended at the other end.