Sitting in my little corner of L&S Electric, I consistently hear our inside sales reps asking for data on motors that customers need replaced or repaired. The one constant is the nameplate data.
But what does the nameplate tell you?
Ever wonder what all those codes on motor nameplates mean? If you are a fan geek, then of course you have…
Here’s a basic overview of the motor nameplate. You should always contact the motor or fan manufacturer with any questions about the letters and numbers on motor nameplates. Remember – if you do not know why a letter or number rating is on the motor nameplate, find out before you connect the motor to a power source.
Motor nameplates have several acronyms that you should be aware of. NEMA is the first name which appears on most motors. It stands for National Electrical Manufacturers Association and represents the motor manufacturer. NEMA standards consist of general rules for good practice in design construction, operating characteristics and frame size. Compliance with NEMA standards is a voluntary decision of the motor manufacturer.
The Frame Size is a number that refers to a set of measurements, including shaft length, shaft diameter, shaft height, and position of the mounting holes in the base plate. Frame sizes have been standardized for over forty years. The original frame sizes are now aptly called “original”. In 1952 “U” frames came around, followed by “T” frames, which are still here today. It is likely that you will still run into some “U” frames, at least for replacement purposes, if you work around motors today.
The most common fractional frame sizes are 48 and 56. The two digit frame number is based on the shaft length in sixteenths of an inch. So, a 48 frame motor will have a shaft length of 3 inches (48 divided by 16), and a 56 frame motor would have a shaft length of 3-1/2 inches. A 48 frame motor will have a shaft length to meet the specification with a diameter of 1/2″. The 56 frame can be used for fractional horsepower motors starting at 1/3 HP and up, but its primary use is for horsepower under 3 HP requiring three phase voltage. Above 3 horsepower. PennBarry uses a 182T, 184T, 213T and 254T. For motors 15 HP and above, we use the 254T frame. Additional letters such as “T-TS-Y-TZ-YZ-DD-C-J”, following the frame number indicate a change from the original standard frame specification.
Another abbreviation often found on motor name plates is NEC which stands for National Electrical Code. This is a group of standards sponsored by the National Fire Protection Association (NFPA) to safeguard people and buildings from danger in the use of electricity for heat, light power and motors, controls and grounding.
Next you will find UL (Underwriters Laboratory). UL is an independent testing organization that tests and certifies under the UL Label. It tests devices, fans, systems and materials for life, fire and casualty hazards for motor manufacturers. UL tests for safe operation in explosive vapors or dust, oil burner systems, window fans and internal overload devices. A UL tested device is usually accepted by most code-enforcing authorities.
Originally, only an “efficiency letter” was put on the motor nameplate. Each letter, starting with A and working on up through the alphabet, denoted a range of full load efficiency. However that system had several drawbacks. First, the single letter could be confused with the design letter or the KVA code letter. (KVA indicated electrical requirements.) Second, the single letter didn’t indicate whether the actual efficiency was toward the low-end or the high-end of the range. Finally, without a copy of the NEMA standard to define the relationships, one could not compare two motors with one another.
The NEMA standard was changed to replace the letters by actual efficiency percentage numbers. The nameplate number signifies a “normal” efficiency, which is an average value taken from “a large population of motors of the same design.” Because of “variations in materials, manufacturing processes, and testing”, no two motors can have exactly the same efficiency.
The Service Factor is the percentage of overloading a motor can handle for short periods of time. You multiply the Service Factor by the horsepower to find the maximum safe load that a motor can carry.
ABM is the surrounding (ambient) temperature above which the motor should not operate (usually 40 °C or 104 °F.)
The image below shows what all the other fields are telling you.