All performance information for a motor is based on the motor being supplied by the power at the potential difference and frequency stated on the nameplate. A motor rating consists of the power output, speed, potential difference, and current specified by the manufacturer.
A typical motor nameplate is shown below. It includes the following information, labeled by numbers in the figure.
1. NEMA designation
- indicates the torque and current characteristics. The most common designations are A, B, C, and D.
|Sr. #||NEMA Letter||Starting Torque||Starting Current||Breakdown Torque||Slip at Full Load|
- indicates the kind of power the motor is designed for. Some motors operate on single-phase ac power, others on three-phase ac power, and still others on dc power.
indicates the frequency of the ac power required to run the motor properly. This frequency is almost always 60 Hz in the United States and Canada. You may sometimes see motors rated for 50 Hz for use in other countries worldwide.
- is the manufacturer’s code number that identifies the motor. It may indicate a general kind of motor sold to many customers, it may indicate a specific kind of motor built for one customer only, or it may indicate only the date the motor was manufactured.
- is the speed of the motor at its rated power, when running on its rated potential difference and frequency. The speed is measured in revolutions per minute. Small motors generally run at one of four speeds, depending on how many poles they have-3450 rpm (2 poles), 1735 rpm (4 poles), 1140 rpm (6 poles), and 825 rpm (8 poles).
- size is defined by NEMA. The most common frame sizes for small motors are 42, 48, and 56. Medium motor frame sizes are 143T through 149T.
7. Time hours
- indicates how long the motor may be operated at one time without over-heating. For most motors, the rating is continuous. That is, the motor can run continuously without overheating.
8. Insulation class
- indicates the class of insulation used in the motor. The classes are defined by NEMA according to the maximum temperatures the insulation can withstand.
Class Maximum Temperature
|Insulation Class||Maximum temperature|
|A||105°C or 221°F|
|B||130°C or 266°F|
|F||155°C or 311°F|
|H||180°C or 356°F|
9. KVA code
- is a letter indicating the locked-rotor power input (measured in kilowatts) per horsepower of rated output. This letter is based on a NEMA code. For example, the letter M indicates a locked-rotor power of 10.0-11.2 kW per horsepower.
- is a NEMA letter code. The first letter indicates the type of motor (T is the NEMA frame designation). The second letter indicates the kind of enclosure (FC indicates a totally enclosed fan-cooled motor).
11. The user or catalog number
- is used by the manufacturer or user to identify the motor.
12. Motor style
- the number is the manufacturer’s specification code. It identifies a set of drawings and electrical specifications necessary to manufacture the motor.
- are identified by number. Any bearing supply house can identify and supply a replacement bearing from this number.
- indicates the normal current drawn at the motor’s rated load, potential difference, and frequency.
- indicates the potential difference of the power supply for the motor.
16. Ambient temperature
- is the temperature in the immediate location of the motor. The standard is 40°C (104°F).
17. Service factor
- indicates how much the motor may be overloaded when operating at its rated potential difference and frequency.
- is the amount of power the motor can produce at its rated speed.