22 Motor Nameplates
Decode your motor’s nameplate
Whether you are looking to replace or repair a motor, when talking to your supplier or service provider, it is important to give them accurate details of the motor you currently have. The most relevant information should be recorded on the motor's nameplate. To help users understand the information on their motor nameplates, Karl Metcalfe, Technical Support at the Association of Electrical and Mechanical Trades, explains what key elements mean.
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o specify a replacement motor or understand the requirements of a repair or rewind, several attributes need to be established. These include information such as the size and format of a motor, its power and speed ratings, how and where it has been designed to be used, its efficiency and a range of other factors. Most motors will have a nameplate that carries this information in a format that meets standards set out by one of two bodies, the International Electrotechnical Commission (IEC) and the National Electric Manufacturers Association (NEMA). Once you understand how the information is presented, it should be
easy to read the nameplate on most motors and pass this information to your supplier or service partner. In figure 1, you will see a typical motor nameplate that meets the IEC standard. Here is what different sections represent. 1 - FRAME SIZE This indicates some of the motor's key dimensions and will usually be at the top of the nameplate as it is an important metric. Frame sizes conform to a standard that defines a motor's dimensions and outputs. The frame size is the height of the shaft's centre from the base of the motor's foot. A 315 frame, as in this example, will have a dimension from foot to shaft of 315mm.
The number will be followed by a letter, S is for a short foot, M is for a medium foot, and L is for a large foot. This letter defines the dimension between the mounting holes on the front and back feet. 2 - POWER The motor's power may be written in kilowatts (kW) or horsepower (hp). It will be written in kW on most motors, but older motors may be rated in hp. 3 - VOLTAGES Where there is more than one voltage figure listed, the delta (symbol) connection is the lowvoltage connection, while the star (symbol) configuration is for a high-voltage connection. The wiring
Figure1: A typical motor nameplate. Image courtesy of WEG. Quarter 4 2021
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