Three-phase electric motor that heats up.

Three-phase electric motor overheating. Discover why and how to fix this problem.

The three-phase electric motor is used in many industrial, agricultural, and even domestic installations. They can be synchronous or asynchronous depending on your application. We find three-phase electric motors on all types of pumps, fans, compressors, mechanical gearboxes, and machine tools.

Their design is extremely simple; they convert electrical energy into mechanical energy. In addition, three-phase asynchronous motors have a standardized design that has standardized industrial equipment. However, even if an asynchronous motor is incredibly reliable, it can still have electrical or mechanical faults.

Among the many faults, some customers come to us because an overheating three-phase motor causes faults in their industrial installations or production lines.

Why is your three-phase asynchronous motor overheating?

Don't be in a hurry, we will answer the question, but it's important to understand that there isn't just one cause for your problem. Several factors can cause your three-phase motor to overheat.

First, it's necessary to know how your motor starts. Are you sure you have a three-phase motor and not a single-phase one? Is your motor AC and not DC? This question is important because the faults can differ depending on your voltage. Three-phase motors can be directly powered by AC current, with a star/delta starter, with a variable frequency drive, or with a soft starter.

Discover the most frequent causes of your three-phase motor overheating.

For three-phase motors directly connected to the grid, we recommend that you first check the tightening of all terminals on the terminal block and all terminals of the circuit breaker, thermal relay, and various junction terminals.

A loose connection can cause abnormal overheating, leading in minor cases to overheating at one of the terminals and in severe cases, to a fire in the entire installation.

After checking the tightness, ensure that no foreign elements such as dust, textile, cardboard, leaves, plastic, or any other external elements prevent air from circulating correctly and thus adequately cooling your three-phase motor. It is important to remember that cleaning is a very important step in maintenance.

A broken fan or a removed fan cover can also cause your three-phase motor to overheat.

Overload, an important factor to consider to prevent a three-phase electric motor from overheating.

Once your motor is properly cleaned, check the current under load. That is, when your motor is driving your application in normal operation. And do this for each phase.

One of the most common causes that could cause a three-phase motor to overheat is overload. Let's take a runner as an example: if he sprints for too long, he will be out of breath and will have to stop. A three-phase motor under overload is exactly the same; if it is overstressed, the nominal current will increase and will quickly cause your motor to overheat.

If it is not properly protected, the winding will melt, and your motor will need to be replaced. Be careful, the current under load must not be higher than that indicated on the nameplate.

If an excessive current can create an overload, undervoltage can also cause a three-phase motor to overheat. A cable section that is too small or a fault in the electrical installation can lead to undervoltage. We remind you that current is equal to power divided by voltage. So, the lower your voltage, the higher the absorbed current.

Undervoltage can cause your three-phase asynchronous motor to overheat.

The voltage of a three-phase motor must be 230V or 400V (plus or minus 5%) depending on your grid supply. If this is not the case, have the power cable section checked by an electrician or contact your energy supplier explaining the problem.

A mechanical fault in your installation can lead to abnormal overheating of your three-phase motor.

One of the most common faults leading to the overheating of a three-phase motor is a mechanical problem.

Your three-phase motor is equipped with two bearings, ball, roller, and in some cases, angular contact bearings. A bearing defect will create mechanical stress and thus an overload.

If you notice an abnormal noise or overcurrent, have your motor checked by the maintenance department, a repair shop, or your motor supplier. They can proceed with the replacement of the bearings and the overhaul of your three-phase motor.

We also remind you to regularly check the lubrication of the bearings. The amount of grease to apply to your motor's bearings can be provided by your supplier.

Furthermore, check elements external to your motor. A faulty bearing on your conveyor, abnormal friction, or overvoltage on your transmission can cause your motor to overheat; the fault is not always related to your motor.

Ambient temperature, an important factor to consider.

An important point we haven't yet discussed is ambient temperature. A three-phase motor should not operate at temperatures above 40°C. If it operates near an oven, or in a room where the temperature is above 40°C, a suitable three-phase motor should be installed. Class H winding, high-temperature bearings, thermal probes... Your motor supplier can advise you on the most appropriate solution for your application.

Overheating three-phase star/delta motor.

For three-phase motors powered in star/delta, it sometimes happens that the star/delta start is done by a manual switch.

This starting principle will gradually start your three-phase motor. This principle under-powers the motor for starting and quickly switches to delta to power the motor correctly.

This starting principle allows your motor to start gradually and reduce the current surge at startup. However, if the operator forgets to switch the motor to delta, your motor will overheat, and the winding will eventually melt. The motor will then have to be replaced. A faulty contactor on your star/delta starter can also cause your motor to overheat.

Three-phase motor on a variable frequency drive overheating.

Some three-phase motors are powered by a variable frequency drive. This principle allows the motor's rotational speed to be varied by changing the frequency via power electronics. It also reduces the current surge at startup and mechanical shocks.

A three-phase motor can operate at a frequency ranging from 0 to 60Hz. However, we remind you that three-phase motors are self-ventilated. The fan installed on your motor cools it when it operates at a nominal frequency of 25 to 60Hz. This speed variation can, in some cases, have an impact on the motor torque and on the overheating of the rotor, stator, and thus the motor casing.

Nevertheless, for synchronous and asynchronous motors operating at a frequency of 25Hz and less, we advise installing forced ventilation, separately powered, to properly cool your three-phase motor. This device will prevent your three-phase motor from overheating.

Three-phase motor overheating? Unsure about how your three-phase motor is functioning? Don't hesitate to consult our article to learn how to check a three-phase motor.