Electric Motor Problems and Solutions

Identifying and addressing the most common electric motor issues is crucial for maintaining efficient and reliable operations. From overheating to bearing failure, understanding the root causes of these problems can help you implement effective solutions.

Common Electric Motor Problems

One of the most prevalent electric motor issues is overheating, which can be caused by a variety of factors, such as overloading, poor ventilation, or a malfunctioning cooling system. By monitoring the motor’s temperature and addressing the underlying causes, you can prevent premature failure and extend the motor’s lifespan.

Bearing failure: Bearing failure can be triggered by improper lubrication, misalignment, or excessive vibration. Implementing a robust maintenance program that includes regular bearing inspections and timely replacements can help mitigate this issue and ensure smooth, uninterrupted operation.

Vibration and Noise: Excessive vibration and unusual noises can be indicative of various problems, such as misalignment, imbalance, or bearing wear. Carefully inspect the motor’s mounting, check for any imbalances, and consider replacing worn-out bearings to resolve these issues.

Reduced Efficiency: If your electric motor is not performing as efficiently as it should, it could be due to factors like a worn-out winding, a faulty capacitor, or a problem with the rotor. Conduct a thorough motor test with Motor Circuit Analysis and/or Electrical Signature Analysis to assess the integrity of the internal components and connections.

Solutions to Resolve Electric Motor Problems

The #1 solution to minimize downtime is to invest in proactive maintenance. 

Regular inspections, cleaning, and monitoring of your electric motors can help identify potential problems before they escalate. From worn bearings to insulation degradation, a trained technician can identify the early warning signs and implement the necessary corrective measures.

By implementing proactive maintenance strategies, such as condition monitoring and predictive maintenance (PdM), you’ll not only enhance the lifespan of your equipment but also drive cost savings and productivity improvements across your operations.


Maintaining optimal operating conditions and ensuring your motors are not overloaded, properly ventilated, and running at the correct voltage and frequency is a necessity. Neglecting these factors can significantly contribute to premature motor failure.

Condition Monitoring

One of the key steps in preventive maintenance is to conduct regularly scheduled assessments of the facility’s motors and rotating machinery. Closely monitor your motors for signs of wear, such as bearing issues, insulation degradation, and imbalances. 

Scheduled assessments with Motor Circuit Analysis should be conducted to monitor conditions over time. Finding and resolving early stage faults before motor failure can greatly reduce production downtime.

Predictive Maintenance

Implementing a comprehensive predictive maintenance program, including electrical signature analysis, vibration analysis and thermography, provides valuable data to identify potential issues before they arise – empowering businesses to make informed decisions proactively.

Conclusion: Take Control of Your Electric Motor Performance Today

Neglecting preventive maintenance is a common mistake that often leads to premature motor failures, unexpected downtime, and skyrocketing repair costs. 

Investing in preventive maintenance is crucial for prolonging the lifespan and reliability of your electric motors. By addressing issues proactively, you can avoid costly and disruptive breakdowns that can grind your operations to a halt.

Prioritize a proactive maintenance strategy and safeguard the smooth, efficient performance of your electric motors.


3-Phase Motor Fault Finding: A Guide

Electric motors are the backbone of many manufacturing and processing operations around the world. Keeping these motors in good condition and running efficiently should be the number one priority of every business.

3-Phase motors use 3 electric currents to provide power to the internal electrical components, such as the stator, rotor, windings and cabling. When a motor has a problem operating, the components must be analyzed to determine the exact location of the issue to be resolved.

Understanding the Basics of 3-Phase Motor Operation

At the heart of a three-phase motor lies the intricate interplay between the stator and rotor components. 

The stator, composed of three windings, creates a rotating magnetic field when supplied with three-phase alternating current. This rotating field induces a current in the rotor, which in turn generates its own magnetic field. The interaction between these magnetic fields produces the torque that drives the motor’s rotation.

The speed of a three-phase motor is determined by the frequency of the supply voltage and the number of poles in the motor’s design. By adjusting the frequency, operators can precisely control the motor’s speed, enabling fine-tuned control over industrial processes.

Three-phase motors offer several advantages over their single-phase counterparts, including higher efficiency, greater starting torque, and more balanced power distribution. These characteristics make them the preferred choice for a vast array of industrial applications, from pumps and compressors to conveyor belts and cranes.

3-Phase Motor Fault Finding Steps

Diagnosing and resolving issues with 3-phase motors can be a complex task, but with the right tools and techniques, you can efficiently identify and address the root causes of common faults that lead to motor failure.

Visual Examination

First, carefully examine the physical condition of the motor, its connections, and the surrounding environment, we can often uncover obvious issues that may be contributing to the problem.

Analysis of Internal Electrical Components

If there are no obvious damages or issues with the motor and its cabling, the next step is to use specialized testing equipment to measure parameters such as winding resistance, insulation resistance, and current draw. These measurements will provide valuable insights into the motor’s internal health and help us pinpoint any electrical faults.

Mechanical Analysis

Finally, the third phase of our fault finding process involves dynamic testing, where the motor’s performance is observed under load. By monitoring the motor’s speed, vibration, and other operational parameters, we can identify any mechanical issues that may be impacting its efficiency and reliability.

Electric Motor Analysis Tools & Technologies

When it comes to maintaining and troubleshooting 3-phase motors, having the right tools and knowledge is crucial. 


One of the most common instruments used to diagnose motors is a multimeter. 

Multimeters allow you to measure crucial electrical parameters such as voltage, current, and resistance across the motor’s windings. 

However, the measurements of these parameters often overlook faults that can be found with other instruments that measure impedance, inductance, phase angle and current frequency.


Another common tool used in motor analysis is the megohmmeter. 

A megohmmeter is an electric meter that measures very high resistance values by sending a high voltage signal into the object being tested.

Megohmmeters provide a quick and easy way to determine the condition of the insulation on wire, generators, and motor windings. 

However, megohmmeter insulation testing only detects faults to ground. Because only a portion of motor electrical winding failures begin as ground faults, many motor faults will go undetected using this method alone.

Surge Testing

A surge test subjects the system to voltage spikes on top of the nominal voltage input to determine weaknesses in insulation.

Surge testing should be avoided for motor analysis because it can be destructive to the internal windings.

Motor Circuit Analysis (MCA™)

Motor Circuit Analysis (MCA™) is a non-destructive, deenergized test method to assess the health of a motor.

Initiated from the Motor Control Center (MCC) or directly at the motor itself, this process evaluates the entire electrical portion of the motor system, including the connections and cables between the test point and motor.

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Electrical Signature Analysis (ESA)

Electrical Signature Analysis (ESA), which encompasses both Motor Voltage Signature Analysis (MVSA) and Motor Current Signature Analysis (MCSA), is an energized test method where voltage and current waveforms are captured while the motor system is running. 

Energized testing provides valuable information for AC induction and DC motors, generators, wound rotor motors, synchronous motors, machine tool motors and more.

Preventive Maintenance to Avoid 3-Phase Motor Failures

Proper preventive maintenance is crucial for avoiding costly 3-phase motor failures. By implementing a proactive approach, you can extend the lifespan of your motors and minimize unplanned downtime.

Condition Monitoring

One of the key steps in preventive maintenance is regular inspections. Closely monitor your 3-phase motors for signs of wear, such as bearing issues, insulation degradation, and imbalances. 

Scheduled assessments of rotating machinery with Motor Circuit Analysis should be conducted to monitor conditions over time. Finding and resolving early stage faults  before motor failure can be imperative to a business’ production.


Equally important is maintaining optimal operating conditions. Ensure your motors are not overloaded, properly ventilated, and running at the correct voltage and frequency. Neglecting these factors can significantly contribute to premature motor breakdowns.

Predictive Maintenance

Additionally, implementing a comprehensive predictive maintenance program, including electrical signature analysis, vibration analysis and thermography, provides valuable data to identify potential issues before they arise. This data-driven approach empowers businesses to make informed decisions and schedule maintenance proactively.


Because a motor’s intricate components are shielded within, 3-phase fault finding is a tricky but possible task with the right approach and the right tools.

Don’t let 3-phase motor problems catch you off guard. Invest in the right tools and techniques, and you’ll be able to keep your critical equipment running smoothly for years to come.


Stator Looseness Diagnosed by Electric Motor Testing Tool

Initial Findings

A 6.6 kV motor that is used to cool the temperature of gas after going through a gas phase polymerization process at a Petrochemical plant was experiencing abnormal symptoms. A technician conducted a vibration test and noticed an abnormal vibration. Another test was conducted with no load and the abnormal vibration remained. The root cause of the vibration was still undetermined. A team from Instrument Resource Co. in Bangkok Thailand was contacted to investigate the motor further to try and determine the cause of the abnormal vibration.

Motor Circuit Analysis™ (MCA™) was performed using the ALL-TEST PRO 7 PROFESSIONAL™. By performing a series of tests, the AT7™ identified the problem after performing the DYN test function. This particular test is designed to verify stator and rotor integrity and health. This test requires rotating the motor shaft. ALL TEST Pro’s patented Dynamic Stator and Rotor Signature test found there was an imbalance in the Dynamic Stator Signature.

Dynamic Signature Analysis

The Green line is the Stator signature and represents the deviation of the mean values during rotation for each phase. The two black dotted lines represent the Rotor Signature and include an upper and lower signature.

The motor was disassembled. Loose stator slot wedges were found. These loose stator slots were causing the excessive vibration and imbalance in the Dynamic Stator Signature.

After the motor was repaired and reassembled another set of tests were preformed with the AT7™. The subsequent test showed there was no longer an imbalance in the Dynamic Stator Signature representing the stator health was in good condition.

About ALL-TEST Pro, LLC.

ALL-TEST Pro delivers on the promise of true motor maintenance and troubleshooting, with innovative diagnostic tools, software, and support that enable you to keep your business running. We ensure the reliability of motors in the field and help to maximize the productivity of maintenance teams everywhere, backing every ALL-TEST Pro product with unmatched motor testing expertise.


Motor Current Signature Analysis on Gearbox Motor


Noise and vibration was investigated on a 7.5 horsepower, 1750 RPM, 575 Vac motor and gearbox using the ALL-TEST PRO™ OL (ATPOL) motor current signature analyzer. One set of data requiring less than one minute of data provided the information necessary. The number of rotor bars, stator slots, bearing information and gears was not available. The lack of information did not hinder the ATPOL in immediately identifying the faults.

Discussion Although lightly loaded, the ATPOL automatically identified casting voids (Figure 1), an electrical fault in the stator (Figure 2), gear problems and identified the number of rotor bars (48) and stator slots (36).

Figure 3 shows the automatic analysis display shown in the ATPOL software.


The ALL-TEST PRO™ MD kit consists of:

  • ALL-TEST PRO™ OL motor current signature analyzer
  • ALL-TEST PRO™ 31 and ALL-TEST IV PRO™ 2000 motor circuit analyzers
  • EMCAT motor management software
  • ATPOL and Power System Manager software modules for EMCAT

Motor Testing: Which Road Will You Take?


Allison Transmission, General Motors Corporation is the world leader in design, manufacture and sales of commercial-duty automatic transmissions, hybrid propulsion systems, and related parts and services for on-highway trucks, buses, off-highway equipment and military vehicles. Aside from its primary location in Indianapolis, IN, Allison Transmission, part of GM’s Powertrain Division, has International regional offices in The Netherlands, Japan, China, Singapore and Brazil and is represented in more than 80 countries via its 1500-member distributor and dealer network.

The Total Motor Maintenance (TMM) concept is a strategy that is used every day from motor inventory and delivery, to testing and reliability of motors.


Quality Network Planned Maintenance

Allison Transmission follows the General Motors North American (GMNA) United Auto Workers Quality Network Planned Maintenance (QNPM) process. This program provides a common process and consistent structure to ensure that equipment, machinery, tools and facilities operate in a safe manner and are available to competitively produce the required products to meet customer needs. There are operating principles that define the fundamental direction the QNPM common process takes. These principles were referenced throughout the planning and implementation process to ensure that all activities are focused on achieving the following objectives:

Provide on going support and direction at the GMNA, division, and plant levels

Ensure that manufacturing is the owner and champion of planned maintenance.

Create opportunities for all employees to participate in the process

Implement the operator involvement concept

Pursue proactive maintenance.

Achieve world-class performance in safety, quality, throughput and cost.

Support continuous improvement


There are twelve interdependent elements in planned maintenance that are integral to a successful process. Each element contributes to and provides support for the others. The linked elements, in total, provide the base for the Planned Maintenance Process (Figure 1):

People Involvement and Organization

Financial Monitoring and Control

Spare Parts Availability



Emergency Breakdown Response

Scheduled Maintenance

Construction Work

Maintenance Tools and Equipment Availability

Reliability and Maintainability

Housekeeping and Cleaning

Production Maintenance Partnership


Supplier Partnership for Motor Program

Commodity Management is the term that Allison Transmission uses for the partnership program with our primary motor supplier. Some of the key features that are realized include improved quality of service and reduced operating and inventory costs. The stored Allison spare inventoried motors are kept at supplier’s warehouse. Subsequently, the supplier meets monthly with Allison personnel and reports on purchases, replacements, delivery time and hard and soft savings (Figure 2).

By using Motor Circuit Analysis (MCA) as one of the technologies (infrared, vibration, ultrasonics, etc.) within the motor program, Allison can more accurately serve our customers’ needs and expectations. Motors can be tested in minutes, even with limited experience, prior to removing and sending them out to a supplier’s motor repair shop. Root cause analysis plays a large role in evaluating the motors with both internal MCA testing and the supplier’s involvement. Upon completion of the motor repair, the supplier supplies Allison with a Repair and a Reason for Repair Report. If the fault is due to contamination, a sample of the contamination found inside the stator windings is collected by the motor shop supplier and passed on to Allison’s technology department for lab analysis. All of this information assists the company in resolving the root cause of the motor problem and failures.

In one department, a servomotor had failed seventeen times in ten months. The supplier was called in to assist in determining a root cause and a corrective action plan. The motor was in a wet harsh area that had a lot of coolant fluid. The vendor suggested a slinger on the motor shaft and a special seal process to keep the motors from prematurely failing. The company’s motor supplier identified these modifications with a yellow stripe to indicate the motor was modified (Figure 3). To date the servomotor has not had another winding failure due to contamination.

This partnership with the motor repair shop has proven to be very effective. Allison has the ability to call 24 hours a day, seven days a week in order to have a stored motor delivered and on its dock within two hours (Figure 4). The response time has been invaluable in planning production schedules. Allison also has access to the motor supplier subject matter experts. As a result, we consider the supplier part of our reliability toolbox. In the end, the motor shop supplier answers to Allison Transmission’s Commodity Management Team, which is comprised of the QNPM rep, electricians from the motor shop and reliability department, the spare parts team, maintenance supervisors and individuals from the finance department.

MCA Overview

Allison Transmission’s motor program is a crucial component within operations. With MCA motors that have problems can be tested to confirm the fault, before being removed and sent out for repair. If a motor problem is not found, the electrician helps the service technician find a root cause. Motors that are difficult to install are tested prior to calling machine repair personnel for installation. Motors in the supplier’s warehouse are audited on a quarterly basis with an MCA test. Some routes have been established due to repetitive motor failures, these motors are tested and trended monthly as part of the MCA process. Motors with pumps are tested prior to rebuilding the pump in order to determine if the motor pump combination may be more economical to replace then to rebuild. The breakdown of the different types of motors repaired or replaced during 2002 can be seen in Figure 4.


According to Delbert Chafey, the Allison UAW co-champion, “Using the motor circuit analysis tool has made a tremendous difference in the way we do business in manufacturing services, and the tide has turned regarding losses incurred from making incorrect judgments, for example, deciding a motor is bad and simply replacing it. The ordering of replacement motors from our commodity manager have dropped off dramatically and as a result the manufacturing services organization can provide operations with greater machine uptime. The results are more parts at a more competitive price, a wider technology base, a better use of (Root Cause Failure Analysis) RCFA and a greater level of confidence for our technology group. Greater uptime + savings + trained tradespersons + great tools for our technology toolbox = success. A great combination!”

Terry Bowen, Allison Transmission QNPM co-champion, attended a motor circuit analysis seminar at the 2001 GM QNPM Symposium and believes the company could benefit from implementing an MCA program in the technology department. In May 2001, during a presentation in the motor shop, Bowen acknowledged the importance of the tool and indicated Allison has purchased three.

Prior to purchasing the ALL-TEST Pro™ motor circuit analyzers, analyzing motors involved a lot of guesswork. Occasionally, motors would be sent to a supplier without a complete diagnosis of a problem. After testing by the supplier, a report back would indicate ‘NO PROBLEM FOUND. Now with the MCA program in operations, Allison sees more uptime on machinery and a decrease in ‘NO PROBLEM FOUND’ reports.

Approximately 50 Allison skilled trades personnel are being trained in the application and use of MCA instruments via an internal eight-hour course taught by Dave Humphrey. The trades involved in the training are electricians, powerhouse stationary engineers, air conditioning and maintenance supervisors.

Motor problems

Motor stator faults found by using MCA vary from turn-to-turn, phase-to-phase, coil-to-coil, ground faults, and rotor faults. Rotor faults, which are more common in 4160-volt motors rather than 480 volt, will have broken rotor bars, eccentricity and casting voids. Looking at the phase angle and current frequency on the ALL-TEST ProTM MCA unit can identify stator faults. By comparing the winding resistance of each phase to one another high resistance connections can be seen. Ground faults can be seen by the insulation to ground test. By comparing the impedance and the inductance readings to each other, contamination can be observed and can range from coolant fluid, oil and water to overloaded windings. The contamination on servo motors will start showing their ill effects months prior to failure. The general trend is that there will be service calls indicating an over-current condition on the panel. After going back and tracking work orders through the Allison CMM system, the over current fault will most likely appear more frequently, then requiring a work order to change servo motors. Area planners have received communication alerting them to the over-current condition and how it can be detected before a servomotor has completely failed. Compared to a reactive course of action, planned maintenance provides for cost avoidance. A clean dip and a bake from the motor shop are cheaper and more efficient than a complete rewind.

The applicable cost avoidance spreadsheet is sequentially shared across the QNPM network according to the following:

MCA work order dispatched

Response to the motor site by an electrician

An MCA test is conducted and analyzed and a determination is made

An action plan is implemented. For example, if a servo motor tests good using MCA, a root cause investigation is initiated to check for other causes of the fault such as a blown fuse, SCR, drive, cable or connecter to the motor. If a cable is replaced, a cost comparison between proactive and reactive is documented based upon maintenance history (Table 1).

Allison Transmission prefers proactive vs. reactive maintenance particularly from a financial perspective. For instance, the total cost savings avoidance at Allison attributable to the MCA program in 2002 was $307,664 (Figure 6).


When testing three-phase motors, the ALL-TEST Pro™ MCA unit works well when performing comparisons between windings. But what about testing single phase? What, no one uses single phase in industrial applications anymore? Allison uses DC motors, which have a set of field windings (two wires) and the interpoles and armature (two wires) for many applications. The Engineering Test department uses eddy current dynamometers in order to put a simulated load on all manufactured transmissions for testing purposes, which also have 2 sets of windings with just 2 wires. How are these two wire devices compared? First an MCA test on the winding, next store the information in the database along with the nameplate information to identify like motors. Finally, compare like windings and the winding with problems will be revealed. (Table 2).


Case Studies

Figure 7: Testing A Machining Center with MCA


Case Study 1 Infrared Thermography (IR)

An electrician running a predictive IR route noticed a hot motor. The motor was a 7.5 horsepower coolant pump in a group of five identical machines. A work order was submitted for a motor circuit analysis to be conducted and subsequently the MCA was completed and analyzed showing no problems with the motor. A work order for vibration analysis was written, and the results determined that the temperature was driven up due to a bearing fault. The coolant pump was replaced and the temperature was in line with the group of machines. This particular machine is a machining center for transmission cases. When a coolant pump motor fails, historically there would be a loss of production and possible an assembly operation shut down.

Case Study 2: MCA vs DMM & Insulation to Ground Test

An electrician running a predictive IR route noticed a hot 5 horsepower motor on a machine with 4 drill heads that performs a drilling operation. The MCA was performed and analyzed and by comparing the impedance and inductance readings, which were clearly not in parallel, the results showed the motor windings were contaminated. Impedance nor inductance cannot be seen with a DMM or an insulation to ground tester. Both the resistance and the insulation to ground test were good. The motor was sent for repairs as this model is not available in the warehouse. MCA was performed to determine the reason why the motor had this contamination. The motor shop did a full autopsy on the motor, and, after cracking open the end bells it was obvious that the problem was fluid in the windings. The unknown liquid was poured into a sample bottle. The motor shop did extensive repairs on the windings, and also applied an epoxy seal to the area after determining the liquid to be a mix of coolant and hydraulic oil. The motor was returned and installed in less than 24 hours. This machine drills a series of holes on the carrier for the transmission. If the machine had run to complete failure, it would have shut down the assembly line. Ordering estimates on a new motor were three days.

Case Study 3 # 8 Air Compressor, 4160 volt 1000 horsepower

On June 18, 2003 the power house tradesmen provided data to the reliability department for review and clarification of ALL-TEST IV PRO™ 2000 readings on the 4160-volt, 1,000-horsepower motor on #8 air compressor. A resistive unbalance of 84.5% was found. The motor was tested at the MCC then at the motor connection lugs. The bad connection at the lugs was found and corrected, reducing the unbalance to 0.17%. This case again showed that MCA is useful, as the 4160-volt connections at the compressor did not have to be taken apart and put back together. The motor did not have to be removed and sent to the motor shop supplier, McBroom Electric. This saved the cost of an unnecessary motor repair and the loss of compressed air for some of the production machines.


Motor Circuit Analysis has made an impact here at Allison. With the NFPA 70E PPE issues approaching, off line motor circuit analysis is very valuable and safe. The motor world will now perhaps be viewed differently from the days of just using a multi-meter and an insulation-to-ground tester. Allison Transmission believes and trusts systems that consistently and correctly allows for proactive maintenance.


About the Author

Dave Humphrey is an eighteen-year veteran journeymen electrician with General Motors. His father is an electrical contractor and Dave started working with his father at age 10. He worked for a variety of contractors prior to going to GM. Dave is certified in motor circuit analysis, infrared thermograph and vibration analysis. Has attended numerous classes on motor diagnostics, ultrasound and root cause analysis. Dave is a graduate of Purdue University and a Certified Master Electrician. Dave has taught motors, transformers, troubleshooting techniques and the National Electrical Code in the GM apprenticeship program. Presently Dave teaches motor circuit analysis classes at Allison. Dave is a Vice President of Habitat For Humanity in his county and provides electrical wiring for all the homes in the program. Dave is a very active family man and Christian.