Figure 7-19.Combination starter with a disconnect switch.
Figure 7-20.Combination starter with a thermal-magnetic circuit breaker.
START-STOP STATION WITH A PILOT LIGHT
Sometimes it is advisable to have a pilot light on the push-button station to indicate whether the motor is running. The lamp usually is mounted on the station and is connected across the holding coil. Such a con- nection is shown in figures 7-24 and 7-25. Figure 7-26 shows a control circuit with the pilot light on when the motor is stopped. Normally closed contacts are needed on this starter. When the motor is running, these con- tacts are open. Contacts are closed when the motor is stopped, and the pilot light goes on.
Modern methods of design and construction have made the electric motor one of the least complicated and most dependable forms of machinery in existence and thereby have made the matter of its maintenance one of comparative simplicity. This statement, however, should not be taken to mean that proper maintenance is not important; on the contrary, it must be given careful consideration if the best performance and longest life are to be expected from the motor. The two major features, from the standpoint of their effect upon the general performance of the motor, are those of proper lubrication and the care given to insulation. Lubrication and insulation protect the most vital, and probably the most vulnerable, parts of the machine.
The designs of bearings and bearing housings of motors have been remarkably improved. However, this advance in design can cause problems. The bear- ings of modem motors, whether sleeve, ball, or roller, require infrequent attention. In the case of older designs with housings less tight than on modem machines, oiling and greasing are done frequently. The perpetuation of this habit causes the oiling and greasing of new motors to be overdone. The result is that oil or grease is copiously and frequently applied to the out-side, as well as the inside, of bearing housings. Some excess lubricant is carried into the machine and lodges on the windings where it catches dirt and there- by hastens the ultimate failure of the insulation.Continue Reading