Making sense of an Electric Motor Nameplate Information

All motor nameplates are not the same. Each manufacturer would have different items on the nameplate but some of the information on the nameplate are standard as required by NEMA(National Electrical Manufacturers Association) and every motor nameplate would contain this information. 

Typically every electric motor nameplate contains

The manufacturer name - This information helps to identify who made the motor 

Enclosure type - Written as ENCL informs us of the enclosure type and the cooling method for which the motor was designed. There are many types of motor enclosures, and each is designed for specific applications guided by what location the motor is expected to operate. the most popular one being Totally Enclosed, Fan-Cooled (TEFC) meaning that there is a fan on the motor shaft that cools the motor. Others include (XPRF) for Explosion Proof, (ODP) for open drip proof, (TENV) for Totally Enclosed, Not Ventilated and (TELC) Totally Enclosed Liquid Cooled

Volts - This gives us information about the rated voltage level of the motor. This is the voltage level at which the electric motor was designed to perform optimally. It is important to note that most good manufacturer’s factor in a 10% tolerance for voltages above or below the nameplate voltage but I suggest you don't feed a motor with overvoltage or under voltage for long periods as it could have undesirable effects on the life of the electric motor.

Full Load Amps (FLA) - is designated on some motors as FLC or simply AMPS This is the most important factor in determining a motor overload. FLA is the amount of current the electric motor will draw from the electrical system when it is fed with the Rated voltage and it is producing its rated horsepower. As the load on a motor increases the amperage required by the motor increases. Consequently, the motor pulls more current from the supply. If for any reason, the motor begins to pull a current that is more than the nameplate FLA of say 50A you are overloading the motor and putting the motor at a risk of overheating, insulation degradation and finally burning the winding.


Service Factor (SF) - is a number that informs us about the maximum allowable overload the motor can tolerate for short periods of time without overheating or damaging the motor. 

The number helps calculate the percentage above the normal motor current (FLA) that is tolerated. For example, a motor with a service factor of 1.15 and FLA of 169A would mean that the motor can pull up an excess 15% above its FLA for a short period of time i.e 169 x 1.15 =194A. The motor would be able to pull 194A intermittently without significant damage or overheating. Generally, it is a bad practice to operate a motor continuously in the service factor area. It is a kind of tolerance meant to cater for short-term faults.


RPM - This is the speed of the shaft at rated voltage and frequency. The rated frequency (Hz) is also part of the standard nameplate data. If you change the frequency the RPM would change as we know Ns (rpm) = 120f/p where f is the freq and p is the number of pole pairs.

PF - This tells you how efficient the motor is in terms of VAR(Volt-Amps-Reactive) usage. It is a ratio of the true power (W) to the apparent power (VA). A PF of 0.9 means that 90% of the power supplied is true power and can be used to do real work while a PF of 0.6 means that 60% of power supplied is true power, therefore, the remaining 40% is reactive power for the magnetizing amperage of the motor. 

More reactive power in the would mean that the wiring would have to carry more current than would be necessary to deliver the same amount of true power. 
 

Efficiency - Usually in percentage. It tells you what percentage of the input electrical energy that would come out of the shaft and do useful work. i.e. a motor rated at 95% efficiency tells you that 95% of the energy you put in would be available for useful mechanical work.

HP - Horsepower is a measure of the power output from the electric motor or power availiable at the shaft of the motor. It is a factor of Torque and RPM. On the nameplate of some manufacturers KW is used instead of HP but Horse power can easily be converted to watts. 1 HP(e) electrical horsepower = 746Watts = 0.746KW

Code - This is also known as Locked Rotor Code or Design code, it tells how many amps the motor would draw when it is first energized. NEMA defines the Locked rotor code with a series of alphabets from A to V.

 Locked rotor means that the rotor is at standstill and if the motor were to stall due to an overload, it would draw the locked-rotor current. The typical behavior of an induction motor is that pulls high current at starting and the locked rotor code [kilovolt-ampere (kVA) per horsepower (Hp)] gives information on the exact magnitude of the in-rush current. 

I have a page showing the locked rotor code table and how to calculate the exact amount if inrush current from the locked rotor code and Rated HP. Generally, the farther the code letter is from A, the higher the inrush current per Hp

Insulation Class - This tells you the temperature that the insulation in the motor is rated for or the thermal tolerance of the motor winding. The type of insulation used in a motor depends on the operating temperature that a  motor is expected to experience.  NEMA established four insulation classes: A, B, F, and H. The table can be found in this post.

AMB - Stands for ambient temperature. It informs us of the maximum ambient temperature at which a motor should operate. Operating the motor under the nameplate ambient temperature rating ensures that the motor will remain within its design temperature rise, meeting all other nameplate data.

Duty Type - There are over 8 types of duty cycles on electric motors by IEC standards but the most popular is CONT(S1). This stands for continuous running duty which tells us that the motor can be operated for long periods at a time with a constant load. Other duty types include Short Time duty, Intermittent Periodic Duty, and non-periodic duty.

Frame Size No - NEMA has standardized on these frame sizes of a motor. This number gives information about mounting and shaft for example  shaft dimensions, spacing of the mounting bolt holes etc. 

In this way from one manufacturer to another, we are going to get similar dimensions making the motor easily interchangeable. eg you could see a number like 143TC or 365T, there is a table where you can look up to fully understand the details of the Frame No

Bearing Number - Information is usually given for both the drive-end (DE) bearing and non-drive end bearing (NDE) Some manufacturers describe it as the bearing opposite the drive end (ODE). Manufacturers also have different bearing numbers that describe bearing type and size. As a maintenance technician, you replace with the exact sizing on the bearing removed. Tinkering is not allowed.


Lubricant type