Motor nameplate is normally located on all produced electric motors. Understanding nameplate information can be hard sometimes, but is essential. In most countries it is a requirement for manufacturers to display all information on the motor’s nameplate, but often this is not the case.
However, when a motor has been in operation for a long time, it is often not possible to determine its operating information because nameplates of motors are often lost or painted over.
- Power factor
- kW or Horsepower
- Full-load speed
- Insulation class
- Maximum ambient temperature
- NEMA // Letter code
- NEMA // Design letter
- NEMA // Service factor
Electrical input //
This data tells you at which voltage the motor is made to operate. Nameplate-defined parameters for the motor such as power factor, efficiency, torque and current are at rated voltage and frequency. When the motor is used at other voltages than the voltage indicated on the nameplate, its performance will be affected.
Usually for motors, the input frequency is 50 or 60 Hz. If more than one frequency is marked on the nameplate, then other parameters that will differ at different input frequencies have to be indicated on the nameplate as well.
This parameter represents the number of AC power lines that supply the motor. Single-phase and three-phase are considered as the standard.
Current indicated on the nameplate corresponds to the rated power output together with voltage and frequency. Current may deviate from the nameplate amperes if the phases are unbalanced or if the voltage turns out to be lower than indicated.
Some manufacturers use type to define the motor as single-phase or poly-phase, single-phase or multi-speed or by type of construction. Nevertheless, there are no industry standards for type. Grundfos uses the following type designation: MG90SA2-24FF165-C2.
Power factor is indicated on the nameplate as either “PF” or “P .F” or cos φ . Power factor is an expression of the ratio of active power (W) to apparent power (VA) expressed as a percentage.
The motor’s nameplate provides you with the power factor for the motor at full-load.
Mechanical Input //
kW or horsepower (HP) is an expression of the motor’s mechanical output rating – that is it’s ability to deliver the torque needed for the load at rated speed.
Full-load speed is the speed at which rated full-load torque is delivered at rated power output. Normally, the full-load speed is given in RPM. This speed is sometimes called slip-speed or actual rotor speed.
Efficiency is the motor’s output power divided by its input power multiplied by 100. Efficiency is expressed as a percentage. Efficiency is guaranteed by the manufacturer to be within a certain tolerance band, which varies depending on the design standard, eg IEC or NEMA.
Therefore, pay attention to guaranteed minimum efficiencies, when you evaluate the motor’s performance.
This parameter defines the length of time during which the motor can carry its nameplate rating safely. In many cases, the motor can do it continuously, which is indicated by an S1 or “Cont” on the nameplate. If nothing is indicated on the nameplate, the motor is designed for duty cycle S1.
Insulation class (INSUL CLASS) is an expression of the standard classification of the thermal tolerance of the motor winding. Insulation class is a letter designation such as “B” or “F”, depending on the winding’s ability to survive a given operating temperature for a given life. The farther in the alphabet, the better the performance.
For instance, a class “F” insulation has a longer nominal life at a given operating temperature than a class “B”.
The maximum ambient temperature at which a motor can operate is sometimes indicated on the nameplate. If not the maximum is 40°C for EFF2 motors and normally 60°C for EFF1 motors. The motor can run and still be within the tolerance of the insulation class at the maximum rated temperature.
This indication shows the maximum height above sea level at which the motor will remain within its design temperature rise, meeting all other nameplate data.
Enclosure classifies a motor as to its degree of protection from its environment and its method of cooling. Enclosure is shown as IP or ENCL on the nameplate.
The frame size data on the nameplate is an important piece of information. It determines mounting dimensions such as the foot hole mounting pattern and the shaft height. The frame size is often a part of the type designation which can be difficult to interpret because special shaft or mounting configurations are used.
Bearings are the component in an AC motor that requires the most maintenance. The information is usually given for both the drive-end (DE) bearing and the bearing opposite the drive-end, non drive- end (NDE).
Besides the above mentioned information, NEMA nameplates have some supplementary information. The most important ones are:
- Letter code,
- Design letter and
- Service factor.
A letter code defines the locked rotor current kVA on a per horsepower basis. The letter code consists of letters from A to V. The farther away from the letter code A, the higher the inrush current per horsepower.
|NEMA code letter||Locked rotor kVA/HP||NEMA code letter||Locked rotor kVA/HP|
|A||0 – 3.15||L||9.0 – 10.0|
|B||3.15 – 3.55||M||10.0 – 11.2|
|C||3.55 – 4.0||N||11.2 – 12.5|
|D||4.0 – 4.5||O||NOT USED|
|E||4.5 – 5.0||P||12.5 – 14.0|
|F||5.0 – 5.6||Q||NOT USED|
|G||5.6 – 6.3||R||14.0 – 16.0|
|H||6.3 – 7.1||S||16.0 – 18.0|
|I||NOT USED||T||18.0 – 20.0|
|J||7.1 – 8.0||U||20.0 – 22.4|
|K||8.0 – 9.0||V||22.4 AND UP|
Design letter covers the characteristics of torque and current of the motor. Design letter (A, B, C or D) defines the different categories. Most motors are design A or B motors.
So, when replacing a motor in an application, it is important to check the design letter, because some manufacturers assign their products with letters that are not considered industry standard which may lead to starting problems.
A motor designed to operate at its nameplate power rating has a service factor of 1.0. This means that the motor can operate at 100% of its rated power.
Some applications require a motor that can exceed the rated power. In these cases, a motor with a service factor of 1.15 can be applied to the rated power. A 1.15 service factor motor can be operated at 15% higher than the motor’s nameplate power.
However, any motor that operates continuously at a service factor that exceeds 1 will have reduced life expectancy compared to operating it at its rated power.
Reference // Motor book by Grundfos (Download)