Importance of Understanding a Motor Nameplate
A replacement motor must be capable of carrying the same load as the motor it is replacing, assuming that the original motor was sized correctly. Much of the information you need to identify an electric motor is contained on the motor’s nameplate. The nameplate also provides some basic information about a motor’s operating characteristics. Proper motor selection is extremely important for safe, efficient, and reliable motor operation. You must fully understand motor nameplate data in order to select the right motor for each application. If an exact match between an old motor and its replacement is not possible, you must be able to determine the most appropriate replacement.
HORSEPOWER AND SERVICE FACTOR
The idea behind the service factor (SF) is to provide an extra margin of safety in motor operation. This extra strength is designed into the motor to allow it to operate at some specified higher load than the motor’s rated load. Basically, the horsepower (HP) stated on the nameplate multiplied by the service factor equals the maximum allowable loading, or total horsepower (THP). The service factor defines the maximum overload the motor can handle when operating at rated voltage and frequency. Thus, a 1 HP motor with 1.5 SF can safely produce up to 1.5 horsepower to move a load (1 HP times 1.5 SF = 1.5 THP). The best procedure in replacing any motor when an exact match of HP and SF is not available is to multiply the nameplate horsepower of the old motor times its service factor to determine the THP. Make certain the replacement motor has a maximum horsepower equal to or slightly higher than the old motor. Handling a continuous load greater than that allowed by the service factor will cause the motor’s thermal protection device to trip. If the situation is not corrected, continued operation will eventually damage the motor.
FRAME SIZE
Standard frame sizes are defined by the National Electrical Manufacturer’s Association (NEMA®*). Each NEMA size defines specific critical dimensions. Frame size is very important in replacing an old motor with a new model or a motor from a different manufacturer. A new motor with a frame size that is different from the old motor may not fit. The most common fractional horsepower motor frame sizes are NEMA 42, 48, and 56. Integral horsepower (IHP) frame sizes are NEMA 140, 180, and larger.
SPEED
The speed at which the motor operates is a critical factor in motor selection. Motor speed must match the needs of the application. Motors are rated according to their speed in revolutions per minute (RPM) at rated horsepower, voltage, and frequency. The actual motor speed under load will vary slightly due to the actual voltage and loading. Motor speed is determined by the number of poles the motor contains. Two-pole motors operate at 3450 rpm, and 8-pole motors at 850 rpm. The replacement motor must have the same number of electrical poles as the motor it is replacing, not just the same approximate speed.
VOLTAGE
The motor voltage rating must match the voltage of the electrical supply. Fractional horsepower motors can have voltage ratings of 115, 200, 208, 230, or 460 volts. The most common ratings are for 115 and 230 volts. A dual-voltage motor, such as a 115/230 volt motor, can be used with either of the listed power supply voltages. Especially in the case of dual-voltage motors, refer to the connection diagram for proper installation.
UNDERSTANDING DATE CODES ON NAMEPLATES
1. Locate the alpha/alphanumeric code in the SER or SERIAL field of nameplate. On VGreen® motors, this code begins with the letter “S” and is placed above the barcode within the nameplate.
2.The first three digits indicate the day of the year the motor was manufactured. The next two digits indicate year the motor was manufactured. S216170000012 = The 216th day of 2017 or August 4, 2017 20418CH = The 204th day of 2018 or July 23, 2018
1. CATALOG OR PART NUMBER - The ID number
2. SERIAL DATE CODE - The month and year manufactured [204th day of 2018]
3. FRAME - Size and type
4. HORSEPOWER - HP x SF = Total Horsepower
5. SERVICE FACTOR
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