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Assuring the Efficiency and Reliability of Repaired Electric Motors

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The Effect of Repair/Rewinding on Premium Efficiency/IE3 Motors
Tests prove Premium Efficiency/IE3 Motors can be rewound without degrading efficiency.

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ANSI/EASA Standard AR100-2020
ANSI/EASA AR100-2020: Recommended Practice for the Repair of Rotating Electrical Apparatus is a must-have guide to the repair of rotating electrical machines. It establishes recommended practices in each step of the rotating electrical apparatus rewinding and rebuilding processes.

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Electromechanical Resource Center

Your electromechanical equipment keeps your systems working. With proper maintenance and care, you can obtain the longest, most efficient and cost-effective operation from general and definite purpose electric motors. 

Each section below describes important tips for getting the most from your electric motors. Get more information by downloading the PDFs.
Electric Motor Rewinding

Electric Motors Can Be Repaired Without Reducing Efficiency

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Installation, Startup + Baseline Information

Get more information on the following steps to ensure a quality installation and reliable operation of a repaired or replaced motor.

Basic Motor System Considerations
Installation
Motor Data + Verification
Motor Foundation + Base
Electrical Connections
Alignment + Vibration
Startup Procedures
Motor/System Baselines
Methods for Determining Motor/System Baselines

 

Basic Motor System Considerations
A motor system typically includes the power supply, mounting, coupling and driven equipment.  

 

Installation
Ensure a quality installation and reliable operation of a repair or replacement motor. 
 
Safety and environmental considerations should be the utmost priority. By adhering to best practices, you will lay a solid foundation for a quality installation and reliable operation of a repaired or replacement motor.
 
 

Motor Data + Verification
Create a motor data verification sheet for recording the nameplate data and electrical and mechanical parameters at the time of installation and startup. These baseline values will be extremely helpful for determining the application’s life-cycle cost and recognizing any change in operating characteristics.  
 
PRO TIP: Attach a digital photo of the nameplate for reference in case of errors in the recorded data.
 
Download the tips and sample data verification sheet below to effectively document this data and work toward a successful installation.
 
 

Motor Foundation + Base
The foundation and base must adequately support the motor’s weight and withstand its torque forces. Concrete foundations should be level and provide ample structural stiffness and vibration damping properties. The base must absorb vibratory forces without exciting resonance in the mechanical system. Steel bases mounted on concrete should be set in grout and securely anchored. Sliding bases used for belt adjustment must rigidly secure the motor. 
 
 

Electrical Connections
  • Follow all applicable electrical codes.
  • Lock out and tag out all potential energy sources before working on the motor.
  • To avoid electrical faults, make sure connections are right and appropriately insulated. Don’t use wire nuts. 
  • Record the motor no-load current on the motor data sheet.
  • Install the connection box cover.
 

Alignment + Vibration
Align the motor to the driven machine, especially if the two are direct-coupled. Misalignment can cause high vibration levels that damage bearing and loosen mountings. Laser instruments are available for aligning both coupled and belted drives. If alignment tolerances aren’t available from the machinery manufacturer, use those found here:
 
 
Alignment procedures include testing for and correcting a “soft foot” – a common problem where the mounting feet aren’t coplanar and therefore do not all sit flat on the motor base. Unless this problem is identified and corrected with shims, tightening the mounting bolts could twist the motor frame. Soft-foot tolerances are suggested in the table above. 
 
 

Startup Procedures
Before installing a motor that has been in storage for more than a few weeks, you’ll want to check a few things to ensure a safe and effective startup. 
  • Inspect and clean the motor to restore it to “as shipped” condition. If the motor has been subjected to vibration, disassemble it and check for bearing damage. Replace any damaged bearings. On grease-lubricated motors, the bearing cavities should have been filled with grease for storage. 
  • To protect the windings from contamination, remove the drain plugs before adding the lubricant specified on the lubrication plate. Then purge the old or excess grease from the bearing cavity by running the motor at no load for 10-20 minutes and replace the drain plugs. If any moisture is present in the purged grease, the bearings are probably rust damaged and should be replaced. 
  • If the motor has been stored for several years, the grease has likely dried out or separated, and the drainpipe is probably plugged up. In that case, it will be necessary to disassemble the motor, clean out the old grease and repack the bearings with the appropriate amount of the specified lubricant. To prevent winding contamination, drain oil-lubricated motors before moving them. 
  • After installation, fill the reservoir with the manufacturer’s recommended lubricant. Test the winding’s insulation resistance and dielectric absorption ratio and record the results. If the IR and DAR test results are satisfactory, perform no-load test operation.  
Before putting a repaired or replacement motor in service, briefly start it to check its operation. If the motor vibrates or emits unusual noises or odors, immediately de-energize it and look for the cause. 
  • If the motor operates normally, allow it to reach full speed before shutting off the power. Always lock out and tag out the motor before connecting the driven load. Once the motor and driven load operate properly, record the full-load voltage and current for all three phases on the motor data sheet for this installation. If possible, also record the input power with load.
  • If the motor is so equipped, monitor the bearing and winding temperatures until they reach a steady state. Document these values as well as the ambient temperature and humidity. For critical applications, record the initial vibration signature of the complete machine as a baseline for a predictive maintenance program.
 

Motor/System Baselines
Maintenance practices have evolved from reactive to predictive, making it possible to operate with fewer spare motors, smaller staffs, less downtime and lower operating costs.

To maximize equipment life, compare baseline installation data from your motor data sheet with future test results as part of a preventive or predictive maintenance program. Trending the data helps operators recognize changing conditions and prevent catastrophic failures. Should a failure occur, trending could also help identify the cause. 

PRO TIP: Local service center professionals can be invaluable resources for this. Find one near you.

The maintenance performed during normal motor operation and planned outages ranges from random to regularly scheduled monitoring, although its frequency may depend on the size, location and critical nature of the application. To draw useful comparisons, baseline variables must correlate with those recorded during the initial startup or after repairs were made.
 
 

Methods for Determining Motor/System Baselines
Changes in motor/system vibration readings provide the best early warning of developing problems in the motor or a system component. Other parameters to monitor may include the operating temperature of critical components, mechanical tolerances, and overall system performance.
 
Motor-specific baselines include records of electrical, mechanical and vibration tests performed when motors are placed in operation or before they are put in storage.
Ideally, baselines would be obtained for all new, repaired and in situ motors.
 
Baselines for motors often include some or all of the following:
  • Load current, speed and terminal voltage. These changes usually indicate that a vital system component is damaged or about to fail. Other electrical tests may include insulation resistance, lead-to-lead resistance at a known temperature, no-load current, no-load voltage, and starting characteristics.

PRO TIP: Some changes in the current and speed may be normal, depending on the type of load.

  • Motor current signature analysis. This test diagnoses squirrel cage rotor problems. It’s more accurate if a baseline is established early in the motor’s life. 
  • Mechanical tests. These normally consist of measuring shaft runout and checking for a soft foot.
  • Vibration. Although overall vibration readings can be used as baseline data, Fast Fourier Transform spectra in all three planes at each bearing housing are preferred.
  • Infrared thermography. This tool can detect changes in the operating temperature of critical motor components, especially bearings.
  • New motor baselines. Comparing factory terminal winding resistance and no-load amps with data taken under load can be useful when monitoring the condition of a new motor or troubleshooting system problems. Factory baselines are often available from the manufacturer or its website. The accuracy of factory data depends on how it was obtained, but it’s usually sufficient for field use. 

Baseline data for a newly installed motor could reveal an error and prevent a premature motor failure. Rather than simply “bumping” a motor for rotation before coupling it to the load, operate it long enough to measure the line current for all three phases, as well as the voltage and vibration levels. 

PRO TIP: Comparing the baselines of a failed motor and its replacement could reveal application- or process-related weaknesses in the system. 

Repaired motor baselines. Service centers usually provide no-load and/or full-load test data for repaired motors, including voltage, current and vibration spectra. Comparing these results with historical baselines and those obtained onsite when the motor is returned to service may confirm the quality of the repair or possibly reveal underlying system problems. For newly repaired motors that have been in operation many years, baseline comparisons are invaluable for root cause failure analysis and may even expose consequential damage from certain kinds of failures. To correctly identify cause and effect and prevent a recurrence, always investigate equipment failure at the system level.

Getting The Most From Your Electric Motors

Getting The Most From Your Electric Motors - coverThis 40-page booklet provides great advice for obtaining the longest, most efficient and cost-effective operation from general and definite purpose electric motors.

This booklet covers topics such as:

  • Installation, startup and baseline information
  • Operational monitoring and maintenance
  • Motor and baseline installation data
  • How to read a motor nameplate
  • Motor storage recommendations

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EASA-Authored Articles Appearing in Industry Publications

Best Practices for Electric Motor Storage

December 2020
Trade press article — Electrical Business

Storing an electric motor for more than a few weeks involves several steps to ensure it will operate properly when needed.  Factors like temperature, humidity and ambient vibration in the storage area also influence the choice of storage methods, some of which may be impractical for smaller machines or need to be reversed before the motor goes into storage.

Advice: Effects of High or Low Voltage on Motor Performance

September 2020
Trade press article — RV News

To ensure the reliability of an RV’s electrical devices, especially electric motors, campers must know the service voltage of the hookup their RV is using. Teaching consumers to check that before they plug in the vehicle could save them many headaches.

Making Shaft Lift Adjustments in Vertical Turbine Pumps

June 2020
Trade press article — Pumps & Systems

Vertical turbine pumps (VTP) commonly have rotors with multiple mixed-flow impellers (sometimes 12 or more) that are supported by a vertical pump motor. Such designs offer a lift adjustment for raising or lowering the pump rotor to properly position the impellers within the bowl. Depending on the type of pump, this may be critical for maximizing pump efficiency and could have a significant impact on motor load (current) and reliability.

How Up-Thrust Occurs in Vertical Turbine Pumps and Provisions to Control It

June 2020
Trade press article — Empowering Pumps & Equipment

Vertical turbine pumps depend on the vertical motor's thrust bearings to support the combined weight of the pump rotor and the motor rotor and to counteract the dynamic down-thrust that the pump impellers generate in lifting the liquid.

Why permanent magnet motors and reluctance motors are finding increased industry application

June 2020
Trade press article — Plant Services

Those familiar with industrial electric motors have heard “DC is dead” for decades as advances in variable-frequency drive (VFD) technology for AC squirrel cage induction motors (SCIMs) seemed destined to replace their DC counterparts in every conceivable application.

But just as DC’s demise was greatly exaggerated, so too is the prospect of successor technologies replacing the installed base of SCIMs any time soon – whether for new applications or replacement motors.

Increasing Motor Reliability

February 2020
Trade press article — Electrical Business

Regardless of the method used to detect winding temperature, the total, or hot spot, temperature is the real limit; and the lower it is, the better. Don’t let excessive heat kill your motors before their time.

Converting motors from horizontal mount to vertical mount

October 2019
Trade press article — Plant Services

Occasionally an end user wants to take a motor designed for horizontal mounting and use it in a vertical position. This article addresses some of the key mechanical factors that should be considered when applying a horizontal ball-bearing motor in a vertical mounting position.

How to deal with wet or flooded motors

October 2019
Trade press article — Plant Engineering

Flooding in the aftermath of tropical storms, including hurricanes, monsoons and cyclones, and with their associated heavy rainfall can shut down hundreds of plants along the Gulf Coast, from Florida to Texas, as well as in other places around the world. And they are doing so more often. To get them up and running again, maintenance departments and motor repairers face the daunting task of cleaning muck and moisture from many thousands of electric motors and generators. The process involved in such situations can take weeks, if not months, and requires special clean-up procedures for motors contaminated by saltwater.

Get your bearings: Electric motor lubrication 101

June 2019
Trade press article — Plant Services

This article looks at the factors that go into determining how often a motor should be lubricated and how much lubricant they should recieve.

Wear ring clearance for centrifugal pumps

June 2019
Trade press article — Pumps & Systems

One of the most common repairs on centrifugal pumps is replacing worn or damaged wear rings. To restore efficient, reliable operation and prevent catastrophic pump failure, it is critical to restore proper clearances between the stationary casing wear ring and the rotating impeller wear ring. Although many pump manufacturers provide clearances and dimensions, some do not. There are plenty of aging pumps around from now-defunct manufacturers for which dimension data is simply not available.

In such cases, the rule of thumb that follows provides some guidance for acceptable running clearances, or the minimum running clearance chart in American Petroleum Institute (API) Standard 610 can be used as a guide.

Considerations for using VFDs with standard motors

June 2019
Trade press article — Plant Engineering

End users desiring speed and/or torque control often buy variable-frequency drives (VFDs) to modify existing applications where a standard induction motor is in place. Frequently, they try to control costs by using that existing standard induction motor. Before taking that path, however, it is best to consider a few areas of concern with the approach.

Selecting Replacement 3-Phase Squirrel Cage Motors

March 2019
Trade press article — Electrical Construction & Maintenance

Selection of replacement motors is usually straightforward if the ratings are equivalent. Sometimes, however, a different type of motor is necessary or desirable. For success in these cases, it is essential that the replacement motor provide the required performance — and do so reliably.

Know your degree-of-protection codes

January 2019
Trade press article — Plant Services

The International Electrotechnical Commission (IEC) standard 60529, “Degrees of protection provided by enclosures (IP code),” addresses the degrees of protection for electrical machines (motors and generators). The “IP” acronym means “international protection” but is sometimes referred to as “ingress protection.” The IP code is commonly displayed on the nameplates of metric machines that are manufactured to IEC standards.

EASA explains upcoming pump standards

January 2019
Trade press article — Pumps & Systems

Starting in January 2020, the U.S. Department of Energy (DOE) will begin implementing the first ever energy efficiency standards for freshwater rotodynamic (centrifugal and axial flow) pumps. These standards will directly affect pump manufacturers and, to a lesser extent, the pump repair market, while ultimately benefiting end users if the new focus can reduce their energy costs.

What’s in a nameplate?

November 2018
Trade press article — Plant Engineering

Whether you're selecting a motor for a new application or a replacement for one that has failed, you need a reliable way to match the capabilities and performance characteristics of various motors with the requirements of the application.

Motor maintenance trends: 6 factors to evaluate

June 2018
Trade press article — Plant Engineering

When faced with an ailing or failed motor, plant operators typically consider whether to repair or replace it. According to a 2014 study conducted by Plant Engineering magazine for the Electrical Apparatus and Service Association (EASA), just more than one-half of plants have a policy of automatically replacing failed electric motors below a certain horsepower rating. While that horsepower rating varied depending upon the plant’s installed motor population, the average rating was 30 hp.

While such policies address a portion of the motors used at most plants, they do not cover what occurs with those motors. That question was addressed in a more recent research project commissioned by EASA that focused on the disposition of electric motors considered for repair.

Best practices for vertical turbine pump repair

June 2018
Trade press article — Pumps & Systems

Vertical turbine pumps (VTPs) are workhorses in the petrochemical, power generation and manufacturing industries, and prolific in municipal water applications that handle the primary intake load. Although these machines are ruggedly built, abrasive sediments in the pumpage take a toll, particularly on line shaft and pump bowl bearings, so periodic overhauls are often necessary. Rather than simply replacing the bearings, however, it is important that repairs address all of the issues needed to restore maximum operating life.

Understand vertical motor bearings

April 2018
Trade press article — Efficient Plant

Bearing construction is a key difference between vertical motors and horizontal motors that are mounted vertically. Vertical motors typically drive pumps using thrust bearings. Horizontal motors rarely have those types of bearings. Understanding relevant construction and configuration factors is crucial when confronting lubrication-related issues that can be associated with vertical-motor bearings.

Practical advice for motor protection

March 2018
Trade press article — Electrical Construction & Maintenance

The Institute of Electrical and Electronics Engineers (IEEE) has published a new standard: IEEE Std. 3004.8-2016, “Recommended Practice for Motor Protection in Industrial and Commercial Power Systems.” If you’re an electrical professional who deals with a broad spectrum of motor protection schemes, including low- and medium-voltage AC and DC motors, then you need to become familiar with this standard.

What's causing your high motor current?

February 2018
Trade press article — Plant Services

The most frequent concern about high current with a three-phase motor is high no-load current. But the broad issue of high no-load current isn’t the only three-phase motor issue to which plants should pay heed.

Understand motor/system baselines

May 2017
Trade press article — Maintenance Technology

Vibration readings provide the best early warning of developing problems in a motor or system component. Other parameters to monitor may include operating temperature of critical components, mechanical tolerances, and overall system performance, including outputs such as flow rate, tonnage, and volume.

Solve vertical pump motor vibration

February 2017
Trade press article — Processing Magazine

High vibration is a common problem for motors that are installed on top of vertical pumps. Its source can be a mechanical issue with the pump, motor or coupling or even hydraulic forces from the pump.

Considerations for using VFDs with standard motors

December 2016
Trade press article — Plant Engineering

There are a few areas of concern involving the misapplication variable frequency drives (VFDs) on a standard induction motor. This article looks at some of those.

Heed design letters when replacing motors

November 2016
Trade press article — Maintenance Technology

Too often, replacement specifications for three-phase squirrel-cage induction motors cover only basic nameplate data such as power, speed, voltage, and frame size, while overlooking other important performance characteristics such as the design letter. This can lead to misapplication of a motor, causing poor performance, inoperability, or failures that result in unnecessary downtime.

How to properly operate a three-phase motor using single-phase power

October 2016
Trade press article — Plant Engineering

There are several methods to operating a three-phase motor using single-phase power to make what would be an otherwise expensive and arduous process a little easier.

Motor connection tips for avoiding costly mistakes

August 2016
Trade press article — Control Engineering

Manufacturers deploy various external connection schemes to produce three-phase induction motors for multiple voltages and/or starting methods, so successful installation depends on using the relevant connection diagram. If this information is lost, damaged, or ignored, a connection mistake could lead to a costly rewind.

Power to the pump

August 2016
Trade press article — Electrical Construction & Maintenance

An important step when selecting a centrifugal pump and an electric motor for an application or when troubleshooting operation issues is to determine how much power the pump should be using.

Sleeve bearing clearance depends on many factors

June 2016
Trade press article — Plant Engineering

“What’s the proper clearance between a shaft and the sleeve bearing it rides in?” Chances are each of us has a rule of thumb for this, probably related to shaft diameter.

My motor failed. Now what?

June 2016
Trade press article — Maintenance Technology

Process downtime is expensive—even more so when it’s unexpected. So, when an electric motor fails, we tend to pull, repair, or replace it, and move on as quickly as possible. In doing so, however, we may miss an opportunity to capture basic information that could help improve the reliability of the application. With a little planning, these data can be gathered with no delay in startup.

Motors: The proactive approach to voltage unbalance

June 2016
Trade press article — Engineered Systems

It’s impossible to balance line-to-line voltages perfectly in three-phase circuits, so they typically differ by a few volts or more. However, if voltage unbalance exceeds 1%, it can markedly decrease the performance and energy efficiency of three-phase motors while increasing the likelihood of premature failure.

Avoid costly motor connection mistakes

May 2016
Trade press article — Maintenance Technology

Manufacturers deploy various external connection schemes to produce three-phase induction motors for multiple voltages and/or starting methods. Be sure to follow the relevant connection diagram, which is usually affixed to the motor or contained in its manual. If the diagram is lost, damaged, or ignored, you could find yourself dealing with a costly rewind.

The importance of impeller design and best efficiency point

May 2016
Trade press article — Electrical Construction & Maintenance

If you work with electric motors and pumps, you’ll eventually encounter a pump curve and one of its key parameters — best efficiency point (BEP). The BEP is the point on the curve where the pump operates most efficiently. Unique to each pump, the BEP is a product of both impeller design and several related pump curve parameters.

How to ensure effective motor repair and rewind

May 2016
Trade press article — Plant Services

Electric motor efficiency can be maintained during repair and rewind by following defined good practices. This article builds on a previous discussion of PM and PdM for three-phase squirrel-cage motors ("PM and PdM for electric motors") by outlining some of the expectations and good practices for repairs of these types of motors.

Can you repair energy-efficient motors? Maybe.

April 2016
Trade press article — Wood Business

Most plant engineers and maintenance staff can attest to the reliability of standard-efficiency motors that have been repaired or rewound using industry best practices. They also know repair can cost far less than replacement, especially when the motor has special features. Despite this, some of them hesitate to have failed energy-efficient motors (NEMA Premium models, in particular) repaired because they’ve heard it degrades efficiency.

So, what’s the right answer? Is the decision to repair, rewind or replace a failed energy-efficient motor as simple and straightforward as you may have heard?

Loaded question: How much do you know about motor load?

January 2016
Trade press article — Plant Services

Right-sizing of three-phase induction motors for different applications – and striking a balance between reliability and efficiency – isn’t always easy, but it can be cost-effective.

Basic procedures assure reliability of stored motors

December 2015
Trade press article — Machinery & Equipment MRO

Downtime is costly, so it pays to have spare motors for critical applications. But unless they are stored properly, those spares may not perform reliably when needed.

Three-phase motor tips: How to evaluate winding temperatures

December 2015
Trade press article — Maintenance Technology

Suspect a three-phase motor is running hot? If you’re right, the unit is either producing more heat than it’s designed for or dissipating less. With excess heat, the main concerns are typically the health of the bearing-lubrication and the winding-insulation system.

Before incurring the expense of pulling the motor, evaluate its winding temperature. This article explains how.

Cool facts about cooling electric motors

November 2015
Trade press article — IEEE Industry Applications

The evolution of electric motor design as it pertains to cooling methods provides insights about better ways to cool machines in service. The array of methods engineers have devised to solve the same problems are fascinating yet reassuring because many things remain unchanged even after a century of progress. This article discusses how motors are cooled and how heat dissipation can be improved for applications that fall outside the normal operating conditions defined by the National Electrical Manufacturers Association (NEMA) Standard MG 1.

Mechanical repairs play a key role in motor repair and reliability

November 2015
Trade press article — Plant Engineering

In a previous article in Plant Engineering ("A systematic approach to AC motor repair," Plant Engineering, April 2015), EASA highlighted the good practices for electrical repair found in ANSI/EASA Standard AR100 Recommended Practice for the Repair of Rotating Electrical Apparatus, and the significant impact they can have on motor efficiency and reliability. But that was only part of the story, because mechanical repairs—and even documentation, cleaning, and inspection—can also markedly affect motor reliability and efficiency.

The quest to find the ‘perfect’ bearing fit

October 2015
Trade press article — Plant Engineering

Much has been said and done to produce the "perfect" fit for rolling element bearings in motors and other rotating equipment. Assembly of these machines requires that either the inner fit to the shaft (journal) or the outer fit to the housing (bore) is able to slide; so if one fit is tight, the other must be loose. While "tight" and "loose" are relative terms that must be defined in the quest for the perfect fit, any fit that's too loose or too tight can lead to early bearing failure and costly downtime.

Cool advice on hot motors

August 2015
Trade press article — Maintenance Technology

The effects of excessive temperature on motor performance are notorious. After moisture, they are the greatest contributor to bearing and winding failures. Understanding the source of increased temperature is key to correcting the problem and improving the reliability of your facility’s motor fleet.

PM and PdM for electric motors: Build the right balance of predictive and preventive tactics to extend long-term operating service life

May 2015
Trade press article — Plant Services

We often hear the terms preventive maintenance (PM) and predictive maintenance (PdM) of electric motors, but far less often do we give consideration to the tasks associated with these methods of maintaining motor operation and extending operating service life.

Keeping it simple: Steps to determine motor’s actual load

October 2014
Trade press article — Plant Engineering

Contrary to popular opinion, bigger isn’t always better—especially when it comes to electric motors. Plant maintenance and engineering departments like having a little extra power available “just in case,” so they sometimes specify larger motors than applications require. But oversized motors cost more to operate—sometimes a lot more.

Understand O-Rings in Submersible Pump Maintenance & Repair Process

June 2014
Trade press article — Pumps & Systems

A leak rate of one drip per minute equals about a liter (quart) of water in three days. For an O-ring on a submersible pump, that is a major problem. O-rings are often used for static seals on submersible pumps. Understanding what makes a good static seal and what causes one to leak is important for pump maintenance and repair technicians.

Common recommendations for stored motors

May 2014
Trade press article — Electrical Construction & Maintenance

When an electric motor will be stored a long time before being placed in service, you must take certain steps to ensure it will be suitable for operation when it’s needed. One practical limitation to recognize is that much of what is done when preparing a motor for long-term storage must be undone when it is moved into operation. Storage procedures generally depend on the size of the motor and whether it will be out of service short term (several weeks) or long term (several months).