Electric Motors: 7 Answers You Should Know

The most used electric device I have ever seen at workplaces is electric motors. As an electrical maintenance engineer understanding motor faults is essential to overcome them if occurred.

In this article, I will answer 7 important questions about electric motor. Let’s dive into details.

Why does an electric motor trip the circuit breaker?

Here under some reasons that lead motor to trip the circuit breaker:

  1. Failure of Thermal Overload Relays. (Circuit overload)

If the thermal overload relays fail, instead of tripping the motor, the motor draws too much current, causing the breaker to trip.

Circuit overload is one of the primary causes of circuit breakers tripping on a regular basis. When a circuit requires greater current, the circuit breaker trips to protect the circuit from being burned and destroyed.

Thermal overload relays are intended to safeguard motors from thermal overload. Because heating is an inherent byproduct of motor activity, the relays safeguard the motor against overheating, also known as thermal overload.

  • Thermal overload relays are classified into three types: bimetallic, eutectic, and electronic.


  • Disconnect/Isolate the relay from the circuit and inspect it individually to ensure that the relay is providing a trip signal at the correct current.
  • Also, check the settings on the relay to ensure that it is correctly configured and that the settings match to those of the circuit breaker.
  1. Breakdown of electrical insulation (ground fault, short circuit or arc circuit)

Occurs when the motor’s insulation starts to deteriorate over time. Aging or overheating produces chemical changes in the insulation, causing it to become more conductive and less efficient in preventing electricity from flowing in unwanted channels between the conductors or to the motor’s frame.

Insulation failures are immediate, especially in the ground wall insulation system, owing to moisture ingression, contamination, or other very distinct phenomena.

Because of this electrical insulation failure, the live wire comes into contact with the bare copper ground wire or a portion of a metal outlet box to which the ground wire is attached. This results in an excess of current flowing again, and the motor trips the breaker.

A ground fault results in an instant decrease in resistance and an increase in electrical flow. As a result, the circuit breaker’s internal mechanism heats up and trips.

Despite the fact that there are other sources of ground faults in motors like:

  1. Water flowing into a motor box
  2. Broken wires
  3. Improperly insulated or damaged wires
  4. Even a buildup of trash inside the motor may all create a ground fault.
  • Ground faults in motors may cause a circuit breaker to trip in order to avoid potentially catastrophic outcomes such as electrical shock, fire, or burns.
  • Electrical insulation failure may also result in a short circuit, which is a direct contact between two points with differing electric potentials.
  • A short circuit creates a surge of current that may reach several hundred times the operating current in milliseconds, causing a breaker to trip.


  • Determine if the electrical insulation failure generated a ground fault, a short circuit fault, or an arc fault.
  • If the issue is a short circuit (can be a bit difficult to diagnose), separate contacts
  • Ground fault relays may be used to monitor the motor; they can be configured to trip at 5-10 A, so that if there is a ground fault due to electrical insulation failure, it will not trip the breaker; instead, the relay will manage the issue.
  1. Circuit Breaker Rating

Safety and protection are provided by circuit breakers and contactors. It also important to make sure that the contactor is in perfect condition. Yes, are also protected by breakers, but if the breaker malfunction, it will greatly affect the functionality of the electric motor.

Depending on the rated current of the motor, It is important to use corresponding circuit breaker in order not to cause the motor to be tripping the breaker.

It’s a good idea to add 10% extra since motor current sometimes surpasses the rated current when the motor is started, and it’s best to maintain the current slightly higher than the rated current of the electric motor.

This tolerant will provide room for any unplanned for behavior of the motor or in case there is an urgent need of another equipment within the same location of the motor.

But if all is right and the motor continues to trip, then maybe there is a need for a proper inspection of the breaker. If everything is in working condition but the breaker keeps tripping, then there is a need to replace it.

  1. Exposure to dust, filth, and chemicals is one of the most prevalent causes of motor failure and can also cause a motor trip a breaker. Foreign items that enter the motor may cause damage to the bearing raceways and balls, resulting in excessive vibration and wear. It may also hinder the cooling fan from functioning, reducing the motor’s ability to manage temperature and raising the danger of overheating.

Motor exposure to dust and chemical prevention is a straightforward procedure. Keep work areas, equipment, and fixtures as clean as possible to reduce the possibility of contaminants entering the motor. Also, keep motors away from grinding equipment that emits a lot of pollution while you’re setting up your workstation.

What causes electric motor to burn out?

  • Overheating:

Electric motors, like any complicated machine with several moving parts, are susceptible to typical performance concerns such as misalignment, bearing wear, and harmonic distortion. Overheating is a typical performance concern in electric motors.

The following are the most often seen causes of motor overheating:

  1. An insufficiently sized motor: Motors come in a range of sizes. Select a motor that is capable of handling the voltage and performance levels required for your project. A motor that is too large wastes valuable energy, whereas a motor that is too small is incapable of managing an excessive workload, resulting in greater stress and heat.
  2. Erroneous voltage supply: A motor may be harmed if it receives an incorrect voltage supply of either too many or too few volts. When a motor does not have enough voltage support, it must work harder to function, resulting in component overheating.
  3. Unfavorable environment: A motor need breathing room in order to operate effectively. If your system is working in a high-temperature environment, it will have trouble swiftly cooling down. Allow sufficient space for the engine to operate.
  4. Incorrect operation: While some motors are meant to run constantly, others are designed to run intermittently. Assure that you just utilize your motor according to the manufacturer’s directions. If an intermittent duty motor is used for a lengthy period of time, it will not have enough cooling time between cycles.
  5. Inadequate ventilation: If something obstructs your electric motor’s ventilation ports, hot air will not escape and will build within the system, causing damage. Regular engine maintenance may help mitigate this risk.
  • Low Resistance:

Another important reason of motor burn out is a lack of insulation or winding resistance in the motor, which may be caused by overheating or moisture absorption by the motor windings.

There is always a need to keep insulation levels high in order to avoid burnout. Low resistance is the most common cause of motor failure and, in my opinion, the most difficult to overcome. Low resistance occurs as a consequence of winding insulation breakdown caused by variables such as overheating, corrosion, or physical damage.

This leads in insufficient isolation between conductors or windings of the motor, which may result in leakages, short circuits, and, eventually, motor failure.

  • Vibration:

The back and forth movement of motorized equipment and components is known as vibration. Vibration in electric motor indicates a problem and if not quickly handled, can lead to motor failure.

Vibration may be caused by a variety of factors at any one time, the most common of which are imbalance, misalignment, wear, and looseness.Vibration may hasten motor deterioration, waste too much energy, and force the motor out of operation, resulting in system downtime.

  • Overcurrent

(also known as a short circuit or a ground fault) is a sudden and fast increase in current over a short period of time (fractions of a second). Equipment and circuits are protected from overcurrent’s by circuit breakers and fuses.

When a bolted fault occurs, for example, such as a line-to-ground or line-to-line fault. With resistance inversely related to current, this leads in a significant amount of current to be taken from the circuit.

For more details about motor burn out read my other article here

Does Electric Motor spark (DC or universal motor)?

Yes, an electric motor may spark when there is a short in the rotor windings, with the copper communicators being the most frequent victim of the burning.

Because of the high temperatures at the brushes, as well as the lubrication oil, it often produced smoke while in operation. Despite the fact that the brush holders are evenly placed, they may be out of place and cause sparking.

Another cause of a spark in a motor is when the holders are too far away from the commutator surface; if the holders are too far away from the commutator surface, it may fail to support the brush adequately, resulting in an ignited spark.

Sparking of the brushes may also occur when the motor is subjected to an excessive load (overloading).

Does Electric Motor smoke?

First and foremost, the presence of smoke in any electric equipment signals that the item is experiencing dangerously high temperatures.

There are a variety of elements that might play a role in this situation. The cause might be anything from wiring problems after repair to weak connections, a utility phase loss, or even the motor itself becoming old.

For example, driving a belt that was jammed with a drilling machine in low gear and that wasn’t actually moving may be a good example.

  • If the motor continues to stall after multiple tries and the protection circuitry of the motor is not up to grade, smoke may actually be seen coming out of the motor.
  • The heat may cause the enamel coating on the motor windings to smoke, and the epoxy casings on the Mosfet drivers can get overheated before the thermal shutdown function is activated.
  • The insulation linked to the conductors in the motor, as well as the circuitry in the motor driver, were both contaminated, which suggests that the motor driver was tampered with.
  • All of these conditions might be a danger factor for the formation of a burning electric motor, as well as a contributing cause to its development. The smoke created by an electric motor is mostly due to the burning away of the enamel on the windings, exposing the copper below.
  • It is only at a commutator bar that the wires come to a conclusion. Each wire is insulated with an enamel coating, which keeps it isolated from the other wires in the loop.

Is it normal for electric motor to become warm?

Yes, its very normal for electric motor to become warm. But, the temperature of the motor should be within limits. Depending on the motor insulation class, we determine the motor temperature limits.

I have written a detailed article about motor temperature rise, you can read it here.

No device is entirely efficient. The lost energy is consumed by friction, back EMF, magnetic saturation, eddy currents, and other losses. Almost all losses result in the generation of waste heat.

Abrasive windings when an electric current passes through it, heat is generated. Because the magnetic field is continually changing as a result of the alternating current source, the iron core sustains certain losses.

This results in the formation of eddy currents in the iron core. This can be reduced, but never eliminated. Additionally, this generates heat. There is some friction, which results in the generation of heat.

The following variables contribute to motor overheating:

    • Environmental conditions
    • Insufficient voltage
  • When a motor is driven continuously, it generates heat, which expands, increasing the pressure on the head gasket.

BLDC technology

Electric fans get hot, the reason for this is because when electric fans are powered continually, the windings of the ceiling fans get heated. This is a common problem with induction motors that operate on alternating current. We have overcome this obstacle using BLDC motors. Fans powered by BLDC motors seldom overheat.

What happens if motor rotor is grounded?

Currents can be formed in the rotor and pass through the bearings if the rotor shaft is grounded between the housing of the bearing or the bearing, producing arcing and damaging the bearings.

This alters the amount of torque produced by the rotor in proportion to the frequency difference between the stator and the rotor, with the stator’s frequency dictated by line power and the rotor’s frequency altering according to speed. Through the slip rings, external resistance may be added or subtracted to change the dynamic of the motor’s speed relationship.

If one of the leads from those slip rings is routed to the ground, the effect will depend on where you are on the torque/speed curve in terms of resistance, and the result is likely to be disastrous regardless of what you do.

The rotor current might be almost as high as the stator current at any level; therefore, aside from an extraordinarily little resistance in that ground fault, energy coming from the grounded rotor’s winding could conceivably be as high as it would be for the case of a grounded stator.

What happens when a motor winding is shorted to ground?

When the motor’s windings are short to the ground, short to one another, or open a rupture in the wire that goes through the winding it will fail and need to replace the damage wound coil. The winding wires have an insulating layer to create an insulation barrier.

If the winding’s insulation wears away near the motor’s casing, the winding becomes bare of wire and shorts to the ground. Typically, the problem is identified inside a slot where the insulation has worn down. The most common reason for grounded winding is water.

A grounded winding is an indication that the motor has to be rewound or replaced. Severe heat, conductive impurities, age, lightning, the pressure of an untight fit of the coil, hot spots that come from damage to the lamination, and excessive damage to the coil are all causes of slot insulation failures.

For more details about motor temperature rise read my article here.

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