THE NAMEPLATE
Electric motors have nameplates that give a great deal of information about the motor. Figure 15–12 illustrates the nameplate of a three-phase induction motor. The nameplate shows that the motor is 10 horsepower, it is a three-phase motor and operates on 240 or 480 volts. The full-load running current of the motor is 28 amps when operated on 240 volts, or 14 amps when operated on 480 volts.
The motor is designed to be operated on a 60-Hz AC voltage, and has a full-load speed of 1,745 RPM. The speed indicates that this motor has four poles per phase. Since the full-load speed is 1,745 RPM, the synchronous speed would be 1,800 RPM. The motor contains a type J squirrel-cage rotor, and has a service factor of 1.25. The service factor is used to determine the amperage rating of the overload protection for the motor. The frame indicates the type of mounting the motor has. Figure 15–13 shows the schematic symbol for a three-phase squirrel-cage induction motor.