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 importance of motor data is that any mistake while connecting or installing the motor could be destructive. 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. I will discuss motor nameplate data, with an example of a Siemens motor nameplate. Let’s get started.
What is not 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
As 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. This voltage is important for safe operation of the motor, as in case of motor running on low voltage its current will increase and could be burnt. While over-voltage cause 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. This means that if the motor load is lower than the full load, then the current will be lower than the full load current. The overload protection device is set according to the value on the nameplate.
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, Efficiency is the percentage of output power to the input power of the motor. The manufacturer of the motor set the efficiency as a percentage. In some cases it is like in the nameplate image we have it is NEM NOM EFF 93
Power of the motor in KW or HP, should be suitable for the 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 our 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 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 IP rating here.
Ambient temperature, 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 is considered as 40°C, Motor Ambient temperature is the maximum allowable temperature of the surrounding that a motor can work properly in.
Motor power factor
Motor power factor, Which shows how effectively your motor using electrical energy. More details about power factor you can see: 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 if the motor is single phase we suppose the power factor as 0.75, If the motor is three phase we suppose it as 0.85 this is the values we meet in most cases.
Motor service factor (SF)
What Is Motor SFA? motor service factor is the percentage of overloading that the motor can handle for short period of times under normal voltage.
In the case of open drip-proof motors (ODP), for example, the standard SFA is 1.15. For example a 1.15 SF 20 hp motor can handle 23 HP for short periods. 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 an performance.
Service factor gives us a little extra “fudge factor” in estimating horsepower needs and actual running horsepower requirements. As a result, windings are kept at a cooler temperature at rated load, contact points are protected against intermittent heat rises, and low or unbalanced voltages are offset.
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 is expected that motors with high Service Factor ratings will likely last for an extended period of time.
As an example, a motor of 1-1/2 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.
Motors that are the most efficient and reliable are those that are designed with a higher S.F., lower FLA and higher S.F.A. Ratings. Using the information on the motor nameplates, we can pick the best motor to replace the broken or damaged one.
Duty cycle of the motor. 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 meet the application requirements as mentioned above.
Motor duty cycle is one of the most important motor specs which should be taken into account when designing the load to select the proper motor for this load type.
Continuous duty cycle (S1)
This is the common duty. It means that 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 35 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).
The most common speeds are 3000 and 1500 rpm. This speed is necessary for the load side. For example, pumps performance depends on its speed.
Motor RPM is a mechanical information, but in my work I need this information when I order a new induction motor for a mechanical load. I ask the mechanical engineer 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, this is because these are the synchronous speed, while the motor never run in this speed and always 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. Mounting dimensions, shaft length, diameter and height and distance between holes all these data 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.
No matter the motor frame is, The motor OEM should have clear dimensions of the motor to help you in choosing the proper one for you application.
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 to need motor specs
When designing a new project or even when purchasing a new motor for any reason, Then 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 but double check the specs and compare it to your requirement. Then rewrite the whole specs again to meet your needs.
Motor data example
Below is the data of three phase induction motor.
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.
- 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 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 repainting the motor make sure to use any insulation method on the nameplate. We use grease in my work.
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- Circuit Breaker Chooser. To help you choose the circuit breaker for motors and non motors loads.