Motor specs or (motor specifications) are the electrical, mechanical and physical data of the motor.
Every motor has its own specs which should be clear on the motor nameplate. The motor data is important because, any mistake while connecting or installing the motor could be destructive and costly. Motor specs are set on the motor nameplate.
Motor nameplate is unique for each motor, It has data specific for that motor. It doesn’t only for electrical specs of the motor, but also it contains other mechanical data like motor frame.
Let’s discuss motor nameplate data, with an example of a Siemens motor nameplate. Let’s get started.
What does motor nameplate mean?
The motor nameplate is a metallic plate supported on the motor body and has important electrical and mechanical data about the motor like voltage, current and connection method.
It’s useful for fast and straightforward understanding type of motor and that motor’s requirements and how to use the motor and keep it in a good condition.
The mechanical structure, electrical functionality, and size specifications of a motor are all specified on the nameplate.
Consistency in nameplate data between manufacturers is one technique to guarantee the identification of interchangeable motors.
Manufacturers may decide to include additional information to aid in the installation, operation, and maintenance of bespoke motors or those made for particular uses, even though NEMA only requires specific data to be provided on the nameplate. The maker chooses the nameplate’s aesthetic.
Why is motor nameplate important?
When buying an electric motor, it’s important to comprehend the specs and other details listed on the nameplate. Nameplate helps to understand the type of motor and that motor’s requirements, like voltage and frequency, quickly and easily.
The proper motor for a given application helps ensure maximum efficiency and longer motor life span and can result in considerable cost savings for your company.
However, a nameplate continues to be vital even after purchase and setting up the motor for the maintenance and following up the motor’s performance. For this reason, the majority are made of steel or aluminum for durability, and the information on the plate is etched throughout readability for the duration of the motor.
When installing a motor, connecting wiring, finding a suitable variable speed drive, or repairing or replacing it, nameplate information is essential.
Understanding this information will enable you to choose the appropriate motor for the application.
However, it is sometimes impossible to ascertain a motor’s operating information after a long period since nameplates are commonly removed or covered with paint.
What is required on a motor nameplate?
I found this question while I was searching for nameplate data. All data on the name plate has its importance, its all about what you need.
But, as electricians or electrical engineers we need electrical data besides some other data. Here below the most important data for us.
- Service factor
- Duty cycle
- Frame, in case we are about to replace a motor we should get the same frame.
Now, let’s go in details to understand motor nameplate.
Electrical motor specs and nameplate understanding
Like any electrical device, electrical motors work on rated voltage and current, but there are some more data should be taken into account.
Operating voltage type AC or DC. Voltage value is important for safe operation of the motor, because, if a motor runs on low voltage, under voltage, its current increases and could be burnt.
While over-voltage causes motor winding insulation failure and then motor burnt.
Connection type either Delta or Star and the connection diagram of the motor in both cases.
Rated current of the motor. This current is important for overcurrent protection design, also for cable and control circuit devices, such as circuit breakers and contactors. All these parts should be designed based on motor rated current.
The current in Amperes on the motor nameplate is the full load current of the motor.
Frequency in hertz. The power source frequency should be suitable for the motor. The motor output power on the nameplate depends on the frequency and rated voltage of the motor.
Motor efficiency is the percentage of output power to the input power of the motor.
Power of the motor in KW or HP, should be suitable for the mechanical load. You can convert kw to hp if required.
You can use the HP to KW and KW to HP converter online.
Insulation temperature (insulation class). The MAX. temperature rise that the winding of the motor can handle in normal operation. Below is Insulation class table.
|Class A||105 Degrees C|
|Class B||130 Degrees C|
|Class F||155 Degrees C|
|Class H||180 Degrees C|
Read also my detailed article : Motor insulation class.
Number of phases, single phase or three phase motor. Its clear that induction motor is not one type, we have single and three phase motors.
This information is listed on the name plate in this shape (3 ̴ or 3 PH)
IP code (ingress protection), this code determines the protection degree against dust, solid objects, and water penetrating the motor body. It consists of two numbers IP XY.
- The firs number X is for dust and solid particles penetrating protection degree. It can be from 0 no protection to 6 fully protected.
- While the second letter Y is for water protection. It can be any number between 0 (No protection) and 8 (Protected against immersion in water for long periods)
IP 67 this motor is fully protected against dust ingress and also can be immersed in water for short periods.
You can find out my other article with more data about What is IP Rating? here.
Motor Ambient temperature is the maximum allowable temperature of the surrounding that a motor can work properly in.
Motors should run properly in a temperature range. This parameter is set on the nameplate as a temperature degree (i.e 40°C AMB).
If motor ambient temperature is not mentioned on the nameplate, then it’s considered as 40°C,
Motor power factor
It shows how effectively your motor uses electrical energy. For more details about power factor you can find it in my other article What is Power Factor (pf)?
What to do if power factor is not on the nameplate? In some cases the power factor is not mentioned on the name plate. Don’t worry in this case:
- For single phase motor, we suppose the power factor as 0.75
- For three phase motors, we suppose it as 0.85
Motor service factor (SF)
Motor SFA or motor service factor, is the percentage of overloading the motor can handle for short period of times under normal voltage and frequency.
The service factor gives the motor loading a tolerance to be cooler in normal load conditions. Some motors could have 1.25, 1.35 and 1.5 SF.
Its important not to load the motor according to the service factor value continuously as this could affect the motor life span and performance.
Service factor helps keeping the windings at a cooler temperature at rated load.
Is a higher service factor better?
Obviously, the higher service factor is better for the motor’s long life. The greater the Service Factor rating of an electric motor, the greater its durability is. It’s expected that motors with high Service Factor ratings will likely last for an extended period of time.
A motor of 1.5 hp with 1.5 S.F.is capable of providing 2.25 hp for short periods of time. As a matter of fact, it is not a good decision to continuously operate a motor over the load capacity of the motor.
The S.F stated on the motor’s nameplate may be shortened if it is continually exceeded. With the same horsepower, motors that have a higher S.F. have a higher “safety factor” and are expected to last longer under tough conditions.
Motor Duty Cycle is the operation sequence and intervals of the motor including no load and full load working, starting and breaking. These operation cases effect the winding temperature and so the motor should be suitable for the load.
Each electrical motor is connected to a mechanical load, the nature and periods of this load working is not the same as other loads.
Some loads need to be 24/7 working while others need just few hours a week. For this purpose its important for you, as an electrical engineer or an professional electrician, to choose the motor which meets the application requirements as mentioned above.
Let’s have a look at duty cycles of motors in more details;
Continuous Duty Cycle (S1)
This is the common duty. It means the motor could work on a continuous load for long time. The motor temperature reaches the degree of thermal equilibrium.
Short Time Cycle (S2)
The load of this type is also continuous but for short periods of time. The motor is allowed to rest and its temperature reach the ambient.
This duty is followed by the number of time in minutes (i.e S2 45 minutes, this is a 45 minutes duty cycle).
Intermittent Duty (S3)
Intermittent periodic duty contains constant loads and periods of rest. This motor duty cycle is much similar to S2 but the motor at rest period doesn’t reach the ambient temperature.
Conveyors that runs at the same constant load for constant periods of time are the best example of this cycle.
Continuous Duty With Braking (S7)
This load cycle is continuous but with electrical breaking and is represented as S7. This includes constant load starting with breaking and there is no rest time.
NEMA design of electrical motors are four types A,B,C and D, each design is suitable for different application.
- NEMA design A: has normal tarting torque and suitable for pumps and fans.
- NEMA design B: high starting torque and suitable for loads with normal starting torques like blowers and pumps.
- NEMA design C: Low starting current and high starting torque, suitable for loads conveyors and positive displacement pumps.
- NEMA design D: very high starting torque. Suitable for loads like cranes.
NEMA design is not only important for load design but also for motor overload protection. Each design has its own overload protection setting.
Mechanical and physical motor data
Electric motor nameplate not only for electrical data but, also for some mechanical and physical specs.
Rotational speed (RPM).
Motor RPM is necessary for the load side. For example, pumps performance depends on its speed.
Motor RPM is a mechanical information, in my work I need this information when I order a new induction motor for a mechanical load. I ask the mechanical engineers about the load RPM to make sure that the motor is suitable for the load.
The most common speeds of the induction motors are 1500 and 3000 RPM, however you will never find these numbers on the nameplate because, these are the synchronous speed, while the motor runs below it. Its common to find the motor speed 1485 RPM or 2890 RPM
The frame is represented on the nameplate in form of letters and numbers. The physical dimensions of the motor body are set as frame size. The motor frame provides the below data:
- Shaft diameter and length.
- Bolt hole mounting dimensions.
- Mounting type (flange or foot mounted motor).
- distance of the shaft from ground.
Some applications need the motor to be painted with special specs because of the environment harsh conditions.
Such as motors working on ships and in desert or even in any high polluted high humidity environment.
When purchasing a new motor you should declare painting type or the environment conditions to get the right motor for your application.
If you will make scheduled greasing for the motor then you should make sure it has greasing holes and its bearing is accepting grease.
For heavy large motors it is necessary to have the lifting holes to be easy in installation and transportation.
Cooling of the motor is one of the important motor specs that should be declared on the nameplate or in the purchasing specs.
TEFC or ODP motors are common on various applications but the most common is TEFC (totally enclosed fan cooled)
See Also my detailed article ODP vs TEFC Motors.
When DO You need motor specs?
When designing a new project or even when purchasing a new motor for any reason, the importance of specs are necessary to get the right motor for your application.
Not all data mentioned above is exist on each motor nameplate.
So, when purchasing a motor don’t just mention the specs from an existing motor nameplate.
How to Write Motor data (example)
Below is the data of three phase induction motor, like we write it in a purchase order.
Three phase induction motor, TEFC, 60 HP, 400V, 50HZ, Delta connected, 0.95 power factor, 1.15 SF, Ins. class F, 1500RPM, 135TS frame, IP 55, S1, ambient temperature 40ºC.
Important notes for the buyer:
- No greasing tube required.
- Lifting hole should be included.
- Painting of the motor should be able to stand out in harsh environment, and high humidity.
- Bolts should be corrosion resist.
Note that, not all specs are on the motor nameplate. But I mentioned it as required.
Tips to keep your motor nameplate
Keeping nameplate of the motor is important because, a motor without a nameplate will need great efforts to find its data. Here under my tips to keep it safe.
- When ordering a new motor, request a spare nameplate with it. We usually do this in my work.
- Take a photo of the nameplate of each motor in the workplace.
- If the motor is about to go in to maintenance process, make sure to carry it with caution. Sometimes the lifting process affect the nameplate.
- In case of painting the motor make sure to use any insulation method on the nameplate. We use grease in my work.
Which power is mentioned on a nameplate of a motor?
The mechanically usable rated output power is the power stated in HP or KW on the motor nameplate.
Additionally, it displays output power that is available at the shaft when all other parameters are adjusted to their rated levels.
Whereas, HP = 0.746 x kW, In contrast, kW = 1.34 × horsepower
Why motor nameplate current is not the same as motor actual current?
In some cases, the motor nameplate current may not match the actual motor current because, along with voltage and frequency, a motor’s displayed current will also correlate with the motor’s rated power output on the nameplate.
In the event that phase balance issues occur, or the voltage turns out to be lower than it should be, the current may differ from the amperes listed on the nameplate.
Besides, the motor nameplate current s the full load current of the motor, it’s much common for motors to not be full loaded, which means lower current than full, nameplate, current.
In other words, the “rated ” value for each parameter of interest is a measure of the maximum safe value and not necessarily the actual value in any particular working condition.
Does motor nameplate have starting current rating?
On the motor nameplate, the starting current value is not stated, but the motor KVA code makes it simple to determine a motor’s starting current from its letter code.
The code letter value, the horsepower, the rated voltage, and the operational power factor of the motor are all mathematically related.
It is crucial to remember that changing a lower code letter to a higher code letter may involve changing other electrical equipment upstream, such as the motor starter.
Calculation and example of motor starting current (LRA) by using NEMA KVA on the motor nameplate.
For the calculation, we should know each value of the NEMA KVA code, so let’s go through these values to review the table given below.
|NEMA Letter Code||Locked Rotor, kVA/HP|
|B||3.15 – 3.55|
|C||3.55 – 3.99|
|D||4.0 – 4.49|
|E||4.5 – 4.99|
|F||5.0 – 5.59|
|G||5.6 – 6.29|
|H||6.3 – 7.09|
|J||7.1 – 7.99|
|K||8.0 – 8.99|
|L||9.0 – 9.99|
|M||10.0 – 11.19|
|N||11.2 – 12.49|
|P||12.5 – 13.99|
|R||14.0 – 15.99|
|S||16.0 – 17.99|
|T||18.0 – 19.99|
|U||20.0 – 22.39|
|V||22.4 – and up|
Consider a motor that has a 50 HP motor rating and a 50 A rated current. using the G code. The motor’s locked rotor current will now be calculated. You can see from the table that the locked rotor range for Code letter G is 5.6–6.29 KVA/HP.
Formula: Motor Starting Current (LRA) = KVA/HP × HP ×1000 =1.732 ×V × I
Lower range of locked rotor current will be as follows:
LRA = 5.6×50×1000 = 1.732 ×440 × I
LRA =280,000= 762 × I
LRA = I = 280,000 ÷ 762
LRA= I = 367 Amperes
Now upper range of locked rotor current will be as follows:
LRA = 6.29×50×1000 = 1.732 ×440 × I
LRA= I = 412 Amperes
Thus, the starting current range for 50 HP motors is 367A to 412A.
What is motor CC on nameplate mean?
CC on the motor nameplate stands for a Certified compliant number on all electric motors that comply with the NEMA Premium efficiency specification.
What does sFA means on motor nameplate?
The amount of current the motor will consume when operating at Full-Service Factor is indicated by the term “Service Factor Amps,” or S.F.A.
Exceeding the S.F.A. shown on the nameplate repeatedly may reduce motor life. With the same horsepower, motors with a higher S.F.A. have a more significant “safety factor” and are predicted to live longer under challenging circumstances.
Higher S.F., lower F.L.A., and higher S.F.A. ratings are used in the construction of the most challenging, most effective motors.
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