19 Essential Information You Can Find On Motor Nameplate

Understanding motor’s nameplate

Motor nameplate is normally located on all produced electric motors. Understanding motor nameplate details 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.

1. Rated Voltage
2. Rated Frequency
3. Phase
4. Rated Current
5. Type
6. Power factor
7. kW or Horsepower
8. Full-load speed
9. Efficiency
10. Duty
11. Insulation class
12. Maximum ambient temperature
13. Altitude
14. Enclosure
15. Frame
16. Bearings
17. NEMA: Letter code
18. NEMA: Design letter
19. NEMA: Service factor

Motor name plate details

1. Rated Voltage

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.

Figure 1 – Voltage on motor nameplate

1.1 Multiple Rated Voltage

Motors usually come with enough terminals to provide alternate connections. This indicates that they can function at a minimum of two different voltages. The primary categories of alternative terminal connections are:

1.1.1 Series-Parallel Motor Connection

The winding of each phase is partitioned into two equal segments. Please keep in mind that this kind of connection is always possible because the number of poles is always a multiple of two.

1. Connecting the two halves in series will result in each half receiving a voltage equal to half of the motor’s rated phase voltage.
2. By connecting the two halves (of phase winding) in parallel, the motor can receive a voltage equivalent to one half of the prior voltage, without changing the voltage applied to each coil. Consult the examples illustrated in Figures 2 and 3.

Figure 2 – Series-parallel connection Y

This connection requires nine motor terminals. The most typical dual voltage system is 220/440 V, which means that the motor is connected in parallel when supplied with 220 V and in series when supplied with 440 V.

Figures 2 and 3 illustrate typical terminal numbering, as well as connection schematics for this type of motor, which can be star or delta linked. The same schematics apply to any other two voltages, as long as one is double the other, for as 230/460 V.

Figure 3 – Series-parallel connection Δ

1.1.2 Star-Delta Motor Connection

Two ends of each phase winding are connected to terminals. By connecting the three phases in delta, each phase receives the total line voltage, which is typically 220 volts (see Figure 4). Connecting the three-phases in star allows the motor to be supplied by line voltage of 220 × √3 = 380 V.

The winding voltage remains at 220 volts per phase.

Figure 4 – Star-delta connection Y – Δ

This connection requires six terminals on the motor and is suitable for any dual voltage, provided that the second voltage is equal to the first voltage multiplied by √3.

Example: 220/380 V – 380/660 V – 440/760 V

In the example 440/760 V, the stated higher voltage indicates that the motor can be powered by a star-delta switch.

1.1.3 Triple-Rated Voltage

The two previous alternate connection arrangements can be achieved in a single motor by dividing the windings of each phase into two halves, allowing for series-parallel connections. All terminals must be accessible in order to connect the three phases in a star or delta configuration.

This means that there can be four options for rated voltage.

1. Prallel-delta connection;
2. Star-parallel connection, being the rated voltage equal to √3 × the first one;
3. Series-delta connection, i. e. the rated voltage being twice the value of the first one;
4. Series-star connection, the rated voltage is equal to √3 × the third one. However as this voltage would be higher the 690 V, it is only indicated as reference for star-delta connection.

Example: 220/380/440(760) V

Note: 760 V (only for starting)

This form of connection requires twelve terminals, and Figure 5 depicts the standard terminal numbering as well as the connection diagram for the three rated voltages.

Figure 5 – Connection diagram for the three rated voltages

2. Rated Frequency

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.

Figure 6 – Frequency on motor nameplate

Three-phase motors designed for 50 Hz operation can be connected to a 60 Hz network. Connecting a 50 Hz motor with the same voltage to a 60 Hz network will result in the following motor performance:

• Same output;
• Same rated current;
• Starting current decreases 17%;
• Starting torque decreases 17%;
• Breakdown torque decreases 17%;
• Rated speed increases 20%.

Note: Please consider the required outputs for motors that drive machines with variable torque and speed.

3. Phase

This parameter represents the number of AC power lines that supply the motor. Single-phase and three-phase are considered as the standard.

Figure 7 – Phase on nameplate

A three-phase system is formed by associating three single-phase voltage system, U₁, U₂ and U₃ which so the phase displacement between any two of them is 120º, which means, the “delays” of U₂ relating to U₁ , U₃ relating to U₂, relating to U₃, are equal to 120º (considering a complete cycle = 360º).

The system is balanced if the three voltages have the same effective value, U₁ = U₂ = U₃, as shown in Figure 8.

Figure 8 – Balanced three-phase system

4. Rated Current

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.

Figure 9 – Rated current on nameplate

5. Motor Type

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.

Figure 10 – Motor type designation

6. Power factor

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. Numerically expressed, power factor is equal to cosine of the angle of lag of the input current with respect to its voltage.

The motor’s nameplate provides you with the power factor for the motor at full-load.

Figure 11 – Power factor also known as cosFI

A motor consumes not only active power, which is converted into mechanical power and heat (losses), but also reactive power required for magnetization, which does not produce work.

In Figure 12, vector P denotes active power, while vector Q indicates reactive power; their sum yields the apparent power S.

[/highlight2]Figure 12[/highlight2] – The Power factor is determined measuring the input power, the voltage and the rated load

The electric motor is crucial in the world’s industry, accounting for almost 65% of energy usage. Consequently, it is imperative to utilize motors with outputs and characteristics well suited to their function, as the power factor varies with motor load.

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Mechanical Input:

7. kW or horsepower

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.

8. Full-load 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.

Figure 12 – Motor efficiency label; Full-load speed; Efficiency in percent and kW or horsepower

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Performance:

9. Efficiency

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.

10. Duty

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.

Figure 13 – Motor duty on the nameplate

Note: Motors designated for continuous duty must be protected against overloads by either an integrated device or an independent device, typically equipped with a thermal relay adjusted to a rated or setting current that is equal to or less than the value of the rated motor power supply current (I_n) and the Service Factor (SF).

How to know if you set the correct current on a motor thermal overload relay

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Reliability

11. Insulation class

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”.

Figure 14 – Insulation class. CI.F(B) = class F with temperature rise B

12. Maximum ambient temperature

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.

Figure 15 – The power output reduction curve shows the performance reduction with increased ambient temperature or increased installation height above sea

The operational temperature threshold of the motor is depending upon the type of insulating material used. In order to conform to the standards, insulation materials and systems, each comprising a combination of several components, are categorized into INSULATION CLASSES. Each is characterized by a specific temperature threshold, namely the maximum temperature that the insulation material or system can withstand continuously without compromising its ability to last.

The insulation classes for electrical machines and their corresponding temperature limitations, as per IEC 60034-1, are as follows:

• Class A ( 105 ºC )
• Class E ( 120 ºC )
• Class B ( 130 ºC )
• Class F ( 155 ºC )
• Class H ( 180 ºC )

13. Altitude

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.

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Construction

14. Enclosure

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.

Figure 16 – Motor frame, enclosure, bearing and grease information on nameplate

Enclosures for electrical equipment must provide a certain level of protection based on their installation features and maintenance accessibility. Consequently, equipment situated in an area exposed to water jets must have a housing that can withstand the impact of the jets at specified pressure and angle of incidence, without allowing water infiltration.

15. Frame

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.

Figure 17 – The frame size data on the nameplate

16. Bearings

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).

NEMA

Besides the above mentioned information, NEMA nameplates have some supplementary information. The most important ones are:

1. Letter code,
2. Design letter and
3. Service factor.

17. Letter code

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.

18. Design letter

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.

19. Service factor

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.

It’s good to know, that 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.

Note that this refers to continuous overload conditions, i.e., a power reserve that gives the motor a better capacity to withstand adverse operating conditions. Service factor should not be confused with momentary overload capacity during few minutes. A service factor = 1.0 means that the motor has not been designed for continuous operation above its rated output.

However, this does not change its capacity to withstand instantaneous overloads.

Suggested Course – Motor Control Schematics Course For True Engineers

Motor Control Schematics Course For True Engineers

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References:

• Motor book by Grundfos
• Specification of Electric Motors by WEG