Providing an exploration into the basics of electric motors, this article focuses on nomenclature, term definitions, components, frames, enclosures, and common motor styles. After reading this article, you will have a broad understanding of what motors are, and how to identify their many components.
Introduction
People and animals were the original power generation units. Animals pulled carts, turned grain mills, and pulled water from wells. Consequently, humans did the chores animals couldn’t do. However, both forms of physical labor were undependable due to lack of funds, disease, and injury. Ancient inventors realized there was a way to do more work and exert less physical input. Thus, the search for a dependable power source was on.
Water
The waterwheel changed the way factories provided energy to their fabrication equipment. Simple in operation, the waterwheel received its power from a running body of water, usually a river or waterfall. The flow of water turned the waterwheel, producing energy. The waterwheel’s energy rotated a large mainline drive shaft that ran through the middle of the building. Individual machines were linked to the main drive shaft via leather belts that transmitted rotational energy
The waterwheel was in use through the Industrial Revolution into the first part of the twentieth century. When the waterwheel worked, energy was abundant and inexpensive; however, there were many inherent potential problems with the energy production.
By design, factories that ran on waterwheels were constructed on, or near a water source, which restricted factory location. From a reliability standpoint, waterwheels produced no rotational energy when water was unavailable. Consequently, dependable power from the waterwheel was unlikely. Depending upon the factory location, ice also stopped the flow of water.
As waterwheel-run mills became popular, competitor factories fought for water usage. In order for mills to ensure a consistent supply of water, dams were built. Unfortunately, water flow slowed or stopped for all the mills downstream of the dam. The resulting water reduction rendered all waterwheels downstream useless. Thus, the need for a more reliable power source was recognized.
Wind
It is unclear when wind was first used to generate power for industrial purposes. However, it is safe to say the idea for windmills originated from the use of sails used on sailing ships.
The first windmills were designed to run grain mills and pump water. There were inherent problems with the dependability of wind as a power source. Factors such as lack of wind, and wrong wind direction rendered windmills useless at certain times of day or year.
Consequently, the likelihood of the mill being unusable at critical times was unlikely. A more dependable source of power was needed to ensure equipment operation at any time of day or night, season, and location.
Steam
Thomas Savery, in 1689, patented a very crude version of a steam-powered engine used for pumping water out of coal mines. Thomas Newcomen and John Calley improved upon Savery’s steam engine in 1712, and again by James Watt in 1769. After further developments, Watt’s steam engine became the standard for all steam engines.
Unlike waterwheels and windmills, the steam engine was not dependent upon a natural source. Therefore, steam engines could be located anywhere. The steam engine proved to be a dependable source of power; however, there was still a need for a less complex, smaller, efficient, and versatile power source to keep up with other technological advances.
Electric Motor
In 1831 Michael Faraday discovered electromagnetic induction and magneto-electric induction. The process was simple: a copper disk (wires attached) is rotated between a magnetized horseshoe. The result is the generation of an electrical direct current.
Simply put, electric motors operate due to electromagnetic force fields. Faraday’s discoveries led to the invention of today’s electric motor.
Electric Motor Functioning
A traditional electric motor generates rotational energy through its shaft. To do this, the electric motor utilizes magnets to create magnetic fields. These magnetic fields work with and against each other to generate motion.
In both direct-current (DC) and alternating-current (AC) motors, the driving torque is provided by the interaction between the magnetic fields set up by the stator and rotor. In the direct-current (DC) motor, the magnetic field is usually stationary and the field, set up by an armature with current-carrying conductors, rotates. The current is supplied to the armature through a commutator and brushes.
In the alternating-current induction motor, the currents in the rotor are supplied by induction. The rotor’s conductors are cut by the stators’ alternating magnetic field (set up by the alternating-current supply to the fields), which induces alternating current in the armature conductors. To gain a better understanding of how electric motors work, let’s look at its components.
Motor Components
The AC electric motor is comprised of the following components:
- Frame – The frame is a housing that holds all internal and external motor components.
- External Fan – Positioned on the exterior end of the motor assembly, the fan blows air across the outside of the motor to prevent overheating.
- Fan Cover – Protects the fan from foreign object damage and protects people from injury.
- Cast Rotor – Also known as the armature. The armature is the assembly of windings. These windings interact with the stator to form the magnetic fields necessary for generating rotation energy.
- Stator – Stationary portion of the motor’s electrical field.
- Front Bearing – Shaft support that reduces friction rotation. The front bearing is located at the end where the shaft extends from the motor housing.
- Rear Bearing – Shaft support that reduces friction rotation. The rear bearing is located at the same end as the external cooling fan.
- Base – Also referred to as the foot mount, the base secures the motor housing to the equipment platform.
- Shaft – The shaft runs longitudinally through the center of the stator, and is supported by the front and rear bearings.
- Capacitor – Affixed to the outside of the motor, the capacitor shifts the phase of the incoming current and feeds the starter winding.
- Front End Shield – Located at the end where the shaft extends from the motor, the front end shield encloses the motor frame and supports the front bearing.
- Rear End Shield – Located at the same end as the external cooling fan, the rear end shield encloses the motor frame and supports the rear bearing.
- Internal Fan – Located within the motor housing, the internal fan circulates air internally
- Nameplate – A tag affixed to the motor to designate motor specification parameters.
- Connection Box – A box affixed to the motor housing where motor connections are made with the power supply.
- End Ring – Located at the end of the rotor assembly, the end rings provide a surface to connect the rotor bars.
Poly-Phase Motors
The poly-phase (3-phase) AC induction motor has a high starting torque, efficiency, power factor, and low current, which is suitable for larger commercial and industrial applications. Poly-phase induction motors are specified by their electrical design type: A, B, C, D, or E, (see Terminology) as defined by the National Electrical Manufacturers Association (NEMA). These designs are suited to particular classes of applications based on the load requirements typical of each class.
Because of their widespread use throughout the industry, many types of general-purpose, three-phase motors are required to meet mandated efficiency levels under the U.S. Energy Policy Act. Included in the mandates are NEMA Design B, T frame, and foot-mounted motors from 1-200 HP.
Motor Nameplate Data
The following nameplate data is taken from the Practical Machinery Management for Process Plants; Machinery Component Maintenance and Repair.
- Horsepower (HP) – Horsepower is the power the motor is capable of putting out continuously.
- Phase (Ph) – Phase data indicate[s] whether the motor is a single or Polyphase machine.
- Hertz (Hz) – Hertz is the frequency of the electrical source. In the United States and Canada, this frequency is 60Hz or cycles per second. In other parts of the world 50Hz is the standard. Because US and Canadian manufacturers import specialized equipment internationally, US motor manufacturers produce 50Hz motors for aftermarket sales purposes.
- Frame Size (Frame) – Frame size is a number that defines the physical dimensions of the motor (see section 0).
- Voltage (Volts) – Voltage is the voltage rating at the motor terminals. Usually satisfactory operation can be expected at a 10 percent variation from the indicated voltage.
- Full Load Current (Amps) – Full load current (amps) is the current draw of the motor connected to the nameplate voltage, loaded at nameplate horsepower and running at nameplate speed. Design Letter (Design) – The NEMA/CEMA design letter governs motor torque and slip characteristics. Design letter definitions can be found in section 0 below.
- Letter Code (Code) – The letter code applies to starting conditions in kilovolts/amps per horsepower (kVA/HP) when starting the motor on full voltage.
- Service Factor (SF) – The service factor indicates the ability of the motor to deliver more than nameplate horsepower. To arrive at the increased rating, multiply the nameplate horsepower by the service factor. The same also applies to the current. With the exception of 1 HP, 3600 revolutions per minute (which have a service factor of 1.25), all standard NEMA general-purpose drip-proof integral horsepower T-frame motors through 200 HP have a service factor of 1.15. T-frame motors above 200 HP, and totally enclosed T-frames have a service factor of 1.0.
- Speed (RPM) – Speed is the speed at which the motor rotor shaft will rotate when loaded with the nameplate horsepower.
Frame Sizes
Here it should be noted that this article is written with the intention of providing a rudimentary overview of AC electric motors. The least confusing, most efficient way to achieve this goal is to utilize one specific standard. For this article, the National Electric Manufacturer’s Association (NEMA) was chosen. Please realize that there are other groups who attempt to coordinate international sizing and performance standards.
“The International Electrotechnical Commission (IEC) is a global organization that prepares and publishes international standards for all electrical, electronic and related technologies…. The IEC’s mission is to promote, through its members, international cooperation on all questions of Electrotechnical standardization and related matters, such as the assessment of conformity to standards, in the fields of electricity, electronics, and related technologies.”
Frame numbers are not intended to indicate electrical characteristics such as horsepower. However, in general, as a frame number becomes higher, the horsepower and physical size of the motor also increase. There are many motors of the same horsepower built in different frames. NEMA frame size only refers to mounting and does not reflect motor body diameter.
Frame Number
In any standard frame number designation, there are two or three numbers. Typical examples are frame numbers 48, 56, 145, and 215. The frame number relates to the ‘D’ dimension (distance from the center of the shaft to the center bottom of the mount). For example, in the two-digit 56 frame, the dimension is 3 1/2″, as 56 divided by 16 = 3 1/2″. For the dimension of a three-digit frame number, consider only the first two digits and use the divisor 4. In frame number 145 for example, the first two- digits divided by the constant 4 is equal to the dimension. 14 divided by 4 = 3 1/2″. Similarly, the dimension of a 213 frame motor is 5 1/4″, as 21 divided by 4 = 5 1/4″.
By NEMA definition, two-digit frame numbers are fractional frames, even though 1 HP or larger motors may be built in them. Three-digit frame numbers are integral frames. The third numeral indicates the distance between the mounting holes parallel to the base. It has no significance in a footless motor.
NEMA Frame Suffixes
There are many NEMA frame suffixes, but the most common are listed below. Contact your motor manufacturer for suffixes not listed.
- C – NEMA – The NEMA C face mount is a machined face with a pilot on the shaft end that allows direct mounting with the pump or other direct coupled equipment. Bolts pass through the mounted part to a threaded hole in the motor face. It is possible to specify a C-face configuration with or without a rigid base.
- D – NEMA – NEMA D Flange Mount is a machined flange with a rabbet for mountings. Bolts pass through the motor flange to a threaded hole in the mounted part. NEMA C face motors are by far the most popular and readily available. D flange mounting can be specified with or without a rigid base.
- H – Indicates a frame with a rigid base that has an F dimension larger than that of the same frame without the suffix H. For example, combination 56H base motors have mounting holes for NEMA 56 and NEMA 143-5T, and a standard NEMA 56 shaft.
- J – J is a NEMA C face configuration, threaded shaft pump motor.
- JM – Close-coupled pump motor with special dimensions and bearings.
- JP – Close-coupled pump motor with special dimensions and bearings.
- M – 63¼4” flange (oil burner).
- N – 71¼4” flange (oil burner).
- T & TS – T and TS are integral horsepower NEMA standard shaft dimensions if no additional letters follow the T or TS.
- Y – Non-NEMA standard mount; a drawing is required to be sure of the dimensions. Can indicate a special base, face, or flange.
- Z – Non-NEMA standard shaft; a drawing is required to be sure of the dimensions.
Frame Prefixes
Letters or numbers appearing in front of the NEMA frame number are the manufacturers’. They do not have NEMA frame significance. Their significance varies from one manufacturer to another.
Motor Enclosures
There are two basic types of enclosures: open and totally enclosed. The enclosure design is important, as it protects the motor from its surroundings, and allows for varying levels of ventilation. The following section segregates the two types of enclosures into their multiple sub-types.
Open Motors
Within the open motor enclosure category there are many different configurations. “The open motor is one in which a free exchange of air is permitted between the surrounding atmosphere and the interior of the motor.
Cooling air is drawn into the motor through ventilating openings at each end and exhausted through similar openings at the bottom of the motor.
Open Drip Proof (ODP) prevents drops of liquid from falling into the motor. These motors are designed for use in areas that are reasonably dry, clean, well-ventilated, and indoors. If installed outdoors, ODP motors should be protected with a cover that does not restrict airflow.
Other Open Motor Types
The following motors are not nearly as popular as the open drip motor but deserve recognition for familiarity purposes.
- Splash-Proof – A splash-proof motor is an open machine in which the ventilating openings are so contracted that successful operation is not interfered with when drops of liquid or solid particles strike or enter the enclosure at any angle.
- Semi-Guarded – A semi-guarded motor is an open machine in which part of the ventilating openings in the motor, usually in the top half are guarded as in the case of a “guarded machine” but the others are left open.
- Guarded – A guarded motor is an open machine in which all openings give direct access to live metal or rotation parts.
- Drip-Proof Fully Guarded – A drip-proof fully guarded motor is a drip-proof machine whose ventilating openings are guarded in accordance with the requirement of a guarded machine.
- Open Pipe-Ventilated – An open pipe-ventilated motor is an open machine except that the admission of the ventilating air is so arranged that inlet ducts or pipes can be connected to them.
- Open Externally Ventilated – Also known as a “force ventilated,” is an open externally ventilated machine that is ventilated by means of a separate motor-driven blower mounted on the machine enclosure.
Totally Enclosed Motors
Like open motors, the totally enclosed motor category has many different configurations. “A totally enclosed motor is one in which there is no free exchange of air between the surrounding atmosphere and the interior of the motor. The interior of the motor is completely covered by the stator frame and end covers, but not sufficiently enclosed to be airtight.
- Totally Enclosed Non-ventilated – TENV motors do not have vent openings. They are tightly enclosed to prevent the free exchange of air, but they are not airtight. TENV relies on convection for cooling, as they do not have cooling fans. They are suitable for use where they may be exposed to dirt or dampness, but not hazardous locations or applications with frequent wash downs.
- Totally Enclosed Fan Cooled – TEFC motors are similar to the TENV except they have an external fan as an integral part of the motor to provide cooling by blowing air over the outside frame.
- Explosion Proof – The Explosion Proof meets Under-writers Laboratories or CSA standards for use in the hazardous (explosive) locations shown by the UL/CSA label on the motor. The motor user must specify the class of explosion-proof motor required. Locations are considered hazardous when the atmosphere contains, or may contain gas, vapor, or dust in explosive quantities.
The National Electrical Code (NEC) divides hazardous locations into classes and groups according to the type of explosive agent. The following list has some agents of each classification. For a complete list, refer to Article 500 of the National Electrical Code.
Class I (Gases, Vapors)
- Group A (Acetylene)
- Group B (Butadiene, ethylene oxide, hydrogen, propylene oxide)
- Group C (Acetaldehyde, cyclopropane, diethyl ether, ethylene, isoprene)
- Group D (Acetone, acrylonitrile, ammonia, benzene, butane, ethylene dichloride, gasoline, hexane, methane, methanol, naphtha, propane, propylene, styrene, toluene, vinyl acetate, vinyl chloride, xylene)
Class II (Combustible Dusts)
- Group E (Aluminum, Magnesium, and other metal dusts with similar characteristics)
- Group F (Carbon Black, Core, or Coal Dust)
- Group G (Flour, Starch, or Gain Dust
- Hostile & Severe – Totally Enclosed Hostile and Severe Environment motors are designed for use in extremely moist or chemical environments, but not for hazardous locations.
Other Enclosed Motor Types
The following motors are not nearly as popular as the TEFC, TENV, Explosion Proof, or Hostile and Severe motors, but they deserve mentioning for familiarity purposes. All of the following open motor descriptions can be found in Peter Walker’s book.
- Dust Ignition Proof – A Dust Ignition Proof motor is a totally enclosed machine whose enclosure is designed and constructed to exclude ignitable amounts of dust or amounts that might affect performance or rating. It also does not permit arcs.
- Waterproof – A waterproof motor is a totally enclosed machine so constructed that it will exclude water applied in the form of a stream from a hose, except that leakage may occur around the shaft provided is prevented from entering the coil reservoir, and provision is made for automatically draining the machine.
- Totally Enclosed Pipe-Ventilated – A totally enclosed pipe-ventilated motor is a totally enclosed machine except for openings so arranged that the inlet and outlet ducts or pipes may be connected to them for the admission and discharge of the ventilating air.
- Totally Enclosed Water-Cooled – A totally enclosed water-cooled motor is a totally enclosed machine that is cooled by circulating water.
- Totally Enclosed Water-Air-Cooled – A totally enclosed water-air-cooled motor is a totally enclosed machine that is cooled by circulating air, which in turn is cooled by circulating water.
- Totally Enclosed Air-to-Air-Cooled – A totally enclosed air-to-air-cooled motor is a totally enclosed machine, which is cooled by circulating the internal air through a heat exchanger, which, in turn, is cooled, by circulating external air.
Adjustable Speed Drive Types
In most industrial applications, mechanical, fluid or eddy current drives are paired with constant-speed electric motors. On the other hand, solid-state electrical drives (also termed electronic drives), create adjustable speed motors, which allow speeds from zero RPM to beyond the motor’s base speed. Controlling the speed of the motor has several benefits, including increased energy efficiency, by eliminating energy losses in mechanical speed changing devices. In addition, by reducing eliminating the need for wear-prone mechanical components, electrical drives foster increased overall system reliability, and lower maintenance costs. For these and other reasons, electrical drives are the fastest growing type of adjustable speed drive.
One Piece Motor / Drive Combinations
Variously called intelligent motors, smart motors, or integrated motors and drives, these units combine a three-phase electric motor and a pulse width modulated (PWM) inverter drive in a single package.
Some designs mount the drive components in what looks like an oversize conduit box. Other designs integrate the drive into a special housing made to blend with the motor. A supplementary cooling fan is frequently used for the drive electronics to counteract the rise in ambient temperature caused by close proximity to an operating motor. Some designs also encapsulate the inverter boards to guard against damage from vibration.
Size constraints limit integrated drive and motor packages to the smaller horsepower ranges, and require programming by remote keypad (either hand-held or panel mounted). Major advantages are compactness and elimination of additional wiring.
One-piece motor and drive combinations can be a pre-packaged solution in some applications. The motor in Figure 10 incorporates drive electronics and cooling system in a special housing at the end of the motor.
AC Drive Application Factors
As Pulse with Modulated (PWM) AC drives continue to increase in popularity, drives manufacturers spend considerable research and development efforts to build programmable acceleration and deceleration ramps, a variety of speed presets, diagnostic abilities, and other software features. Operator interfaces have also improved with some drives incorporating “plain-English” readouts to aid set-up and operation. Plus, an array of input and output connections, plug-in programming modules, and off-line programming tools allow multiple drive set- ups to be installed and maintained in a fraction of the time. All these features simplify drive applications. However, several basic points must be considered: torque, speed, current, power supply, control complexity, and environmental factors. Contact your motor and drive manufacturer for the proper drive selection.
Motor Considerations With AC drives
One drawback to Pulse Width Modulated (PWM) drives is their tendency to produce voltage spikes, which can damage the insulation system and bearings used in electric motors. This tendency is increased in applications with long cable distances (more than 50 feet) between the motor and drive, and with higher-voltage drives. In the worst cases, the spikes can literally poke holes into the insulation. To guard against insulation damage, some manufacturers now offer inverter-duty motors with special insulation systems that resist voltage spike damage.
Particularly with larger drives, it may be advisable to install line reactors between the motor and drive to choke off the voltage spikes. In addition, some increased motor heating inevitably occurs due to the inverter’s synthesized AC waveform. Insulation systems on industrial motors built in recent years and inverter-duty motors, can usually tolerate this. A greater cooling concern involves operating for an extended time at low motor RPM, which reduces the flow of cooling air, especially in constant torque applications where the motor is heavily loaded. Here, secondary cooling such as a special constant- speed blower kits can be added in the field to provide additional cooling to motors operated at low RPM as part of an adjustable speed drive system.
Electric Motor Mounting
Unless specified otherwise, motors can be mounted in any position or any angle.
However, unless a drip cover is used for shaft-up or shaft-down applications, drip-proof motors must be mounted in the horizontal or sidewall position to meet the enclosure definition. Mount motors securely to the mounting base of equipment, or a rigid, flat surface, preferably metallic.
- Rigid Base – A rigid base is bolted, welded, or cast onto the main frame and allows the motor to be rigidly mounted on equipment.
- Resilient Base – A resilient base mount has isolation or resilient rings between motor mounting hubs and the base to absorb vibrations and noise. A conductor is embedded in the ring to complete the circuit for grounding purposes.
- NEMA C Face Mount – The NEMA C face mount is a machined face with a pilot on the shaft end which allows direct mounting with the pump or other direct coupled equipment. Bolts pass through the mounted part to the threaded hole in the motor face.
- NEMA D Flange Mount – NEMA D Flange Mount is a machined flange with a rabbet for mountings. Bolts pass through the motor flange to a threaded hole in the mounted part. NEMA C face motors are by far the most popular and most readily available. Some manufacturers stock NEMA D flange kits.
- Type M or N mount – The Type M or N mount has special flanges for direct attachment to the fuel atomizing pump on an oil burner. In recent years, this type of mounting has become widely used on auger drives in poultry feeders.
- Extended through-bolt motors – Extended through-bolt motors have bolts protruding from the front or rear of the motor by which it is mounted. This is usually used on small direct drive fans or blowers.
Application Mounting
For direct-coupled applications, align the shaft and coupling carefully, using shims as required under the motor base. Use a flexible coupling, if possible, but do not use it as a substitute for good alignment practices.
Pulleys, sheaves, sprockets, and gears should generally be mounted as close as possible to the bearing on the motor shaft, thereby lessening the bearing load.
The center point of the belt, or system of V- V-belts, should not be beyond the end of the motor shaft. The inner edge of the sheave or pulley rim should not be closer to the bearing than the shoulder on the shaft but should be as close to this point as possible.
The outer edge of a chain sprocket or gear should not extend beyond the end of the motor shaft.
To obtain the minimum pitch diameters for flat-belt, timing-belt, chain, and gear drives, the multiplier given below should be applied to the narrow V-belt sheave pitch diameters in NEMA MG 1-14.444 for alternating current, general-purpose motors, or to the V-belt sheave pitch diameters as determined from NEMA MG 1-14.67 for industrial direct current motors.
Drive Multiplier
- Flat Belt* 1.33
- Timing Belt+ 0.90
- Chain Sprocket 0.70
- Spur Gear 0.75
- Helical Gear 0.85
* This multiplier is intended for use with conventional singly-ply flat belts. When other than single-play flat belts are used, the use of a larger multiplier is recommended.
+It is often necessary to install timing belts with a snug fit. However, tension should be no more than that necessary to avoid belt slap or tooth jumping.
Electric Motor Operations
Losses
Losses in a motor result from the rotation of its movable parts and the flow of electricity through its conductors; these are generally classified as mechanical losses and electrical losses, and all are manifested as heat. [3]
Mechanical power is lost in four ways:
- The extra power is needed to overcome bearing friction.
- The extra power needed to break away the inertia of the rotor at a standstill.
- The extra power is needed to overcome the friction caused by the brush contact on the commutator (DC only).
- The extra power is needed for the rotor to overcome the resistance of air.
Electrical power is lost in the conductors of both the field and conductors, generally known as copper losses. Losses caused by the action of the magnetic fields are referred to as iron losses and are given off as heat. [3]
Efficiency
Because all machines have some losses, their efficiencies are never 100%. That is, the output power is never the same as the input power. Usually expressed as a percentage, efficiency is the ratio between output and input power. [3]
With the ever-increasing cost of utility energy and the overall cost-effectiveness of the consumer, motor manufacturers are always attempting to produce motors of premium efficiency. The proof of the premium efficiencies’ effectiveness is found in the utilities’ practice of issuing rebates to users who employ motors that consume less electricity. The logic stems from the utilities’ economic concerns, whereby they conclude it is more economically feasible to conserve
energy than it is to build more power plants. To encourage this conservation effort they reward those conscientious electricity users with rebates. Contact your local power utility
/ municipality for the latest programs, and information on premium efficient motors ratings.
Temperature
Temperature plays an important role in the efficient running of an electric motor. It is important to remember that when a motor is not running efficiently, more energy is consumed. This consumption relates directly to the total cost of your motor’s operation. It is to your advantage to guarantee proper precautions are taken to ensure your motor is running cool. Contact your motor manufacturer for specifics on the effects of temperature on your electric motor and its application.
Handling & Storage
Handling
If your motor is not being placed immediately into service it should be stored in a clean, dry, and relatively warm place (not less than 60°F or 15°C). [2]. However, before storing, properly inspect it upon delivery for damage. Consult your motor manufacturer for specific motor handling requirements.
Never attempt to lift a heavy motor by yourself. If the motor came on a pallet, use a forklift to move the motor. If an eyebolt is supplied on top of the motor, use a strap or chain rated for the weight of the motor, in conjunction with a crane or forklift to move it. Some motors do not come with lifting fixtures; in this case, use caution so as not to damage the motor or injure people. Never move or lift a motor by the shaft. Doing so may cause damage to the motor bearings, seals, and rotor/stator assembly.
Storage
Again motors should be stored in a clean dry place. More importantly, the electric motor should be kept in an area where it will not experience severe temperature changes. Extreme temperature changes cause condensation within the motor assembly, which corrode or rust unprotected surfaces. If it is impossible to store the motor under cover, contact your manufacturer for proper protection from the elements and possible insect and rodent infestation.