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Guidelines for motor installations.

A strong working knowledge of installation techniques is vital to the effective operation and maintenance of motors.Today's modern motors require your consideration of all aspects of selection, application, and maintenance as well as details of assembly, hardware, and the interrelationship of components and materials. As a result, installation of these motors is more important than ever before.Proper

A strong working knowledge of installation techniques is vital to the effective operation and maintenance of motors.

Today's modern motors require your consideration of all aspects of selection, application, and maintenance as well as details of assembly, hardware, and the interrelationship of components and materials. As a result, installation of these motors is more important than ever before.

Proper motor installation is essential in obtaining top-quality operation, efficient performance, and maximum reliability. Whether you're an installer, engineer, or maintainer, this work demands close coordination, planning, and teamwork with other disciplines.

Receiving and handling

When receiving a motor, you should thoroughly inspect it for dents or other signs of damage before the motor is moved from the shipper's truck. Also, examine all literature provided with the machine. Do not remove tags pertaining to assembly, storage, lubrication, and operation. You should file this literature, along with any specifications and drawings pertaining to the machine, for reference during installation and for guidance during start-up and operation.

On smaller units, you should turn the shaft by hand to verify that it turns freely. If equipped with antifriction bearings, these motors normally will be prelubricated and ready for operation.

Large motors and engine-generator sets having sleeve bearings are usually shipped without lubricating oil in the bearing; often they are filled with an anti-rust fluid. These should be inspected through the sight glass and bearing drain openings. Check for any accumulation of moisture and remove any traces of oxidation. Then, fill the bearing reservoirs to normal level with a high-grade industrial lubricating oil. Remove any dirt, metal filings, or other contamination that might appear in the oil, or replace the oil.

Always check the nameplate for proper voltage, phase, frequency, horsepower, etc.

Large motors are sometimes shipped disassembled. When assembling, be sure all mating parts are clean. This can be done with a magnet, vacuum cleaner, or dry compressed air (air pressure less than 60 psi).

When handling machines by hoist, be sure to use lifting bolts if they are provided. Always disconnect any coupling between the motor and its load before lifting, unless the base is strong enough to assure that shaft or bearings will not be damaged.

Safety procedures

Handling of large, heavy motors should be supervised by experienced and qualified personnel. Safety of workers and avoidance of damage to the motor are primary considerations. Details concerning types of cranes, hoists, jacks, rollers, wire ropes, cables, hooks, slings, and the many other aspects of moving heavy apparatus are extensive.

Safety is of paramount importance during the installation, start-up, and operation of a motor, and begins with the proper design, application, and selection of the motor and associated components. Be sure that the motor has been well matched to handle the type of load to be driven.

Check that gears, belts, driven machinery, etc. are guarded so that anyone near the installation will not be harmed by accidental contact.

All personnel involved with the installation should be familiar with NEMA MG2, Safety Standards For Construction and Guide For Selection, Installation, and Use of Electric Motors and Generators.

Pertinent NEC rules, especially Art. 430, and all local safety rules must be observed. In addition, OSHA rules must also be studied and followed during the installation of motors and controls. These regulations are included in Part 1010 of the Occupational Safety and Health Standards. You can obtain a copy of this document from any local OSHA office.


Always try to locate the motor in the best possible environment: A clean, dry, cool location. The type of environment in which the motor will operate determines the type of enclosure. Available enclosures, which have been standardized by NEMA, simplify selection.

An open-type motor is usually the best choice for installation in locations reasonably free of moisture, dust, or lint. Be sure space is available for maintenance or replacement. Open motors having commutators or collector rings must be located or protected so that sparks cannot reach adjacent combustible material. This does not preclude the mounting of such motors on wooden platforms or floors.

Dripproof motors are intended for use where the atmosphere is relatively clean, dry, and noncorrosive. With these motors, you should keep windings clean by using a soft brush, cloth, or suction.

Totally enclosed motors may be installed where dirt, moisture, and corrosion are present, or in outdoor locations. If a drain plug is provided in the end bracket or bell, it should be removed periodically to drain any accumulated condensation.

Be certain that the enclosure is suited to the surrounding environment and that there is adequate ventilation to assure operation at or below motor design temperature.

Problem locations. In addition to open (general-purpose), dripproof, and totally enclosed fan-cooled (TEFC), a number of other designs are available for specific environments and applications. When extreme environments or unusual conditions exist (high temperatures, excessive vibration, etc.), you'll have to incorporate special enclosures or arrangements into the installation.

Moisture problems require special consideration. Here, suitable guards or enclosures must be provided to protect exposed current-carrying parts and the insulation of motor leads where dripping or spraying oil, water, or other injurious liquid may occur, unless the motor is specially designed for the existing conditions.

For standby service or for damp-location operation, a low single-phase voltage (on the order of 5% to 10% of rated voltage) is sometimes applied to the windings to combat moisture. Some larger motors are available with built-in strip heaters or tubular-type space heaters for this purpose.

Check ambient temperatures. Be sure that the motor will not be exposed to an ambient temperature exceeding 40 [degrees] C, since excessive heat shortens machine life significantly. If the motor windings are encapsulated, the insulation will be exposed to a higher than normal temperature. The increased temperature of an open dripproof motor with a 1.15 service factor can be compensated for by reducing the service factor or by supplying a higher-rated insulation.

Permitted temperature rise of different insulations is based on operation of the motor at altitudes of 3300 ft or less. When this elevation must be exceeded, there are several alternatives. If the motor has 1.15 service factor, then it can be operated at unity factor at altitudes up to 9000 ft in a 40 [degrees] C ambient.


A rigid foundation is essential for minimum vibration and proper alignment between motor and load. Concrete, reinforced as necessary or required, makes the best foundation, particularly for large motors and driven loads. In sufficient mass, it provides rigid support that minimizes deflection and vibration. The foundation may be located on soil, structural steel, or building floors, provided the total weight (motor, driven unit, and foundation) doesn't exceed the allowable bearing load of the support. Allowable bearing loads of structural steel and floors can be obtained from engineering handbooks.

Building codes of local communities give the recommended allowable bearing loads for different types of soil. For rough calculations, the subfoundation should be approximately 2 1/2 tunes the total unit weight.

Whether the motor base is concrete or steel, it must be level. If concrete, be sure it's not too high. A motor can always be raised by use of shims; but reduction of height would be difficult because it would require removal of some of the concrete surface.

Before pouring the concrete foundation, you should locate foundation bolts by using a template; this will provide for secure anchorage (not rigid). You should reference certified drawings of the motor, base, and driven unit for exact location of foundation bolts. Also, you should install a fabricated steel base between motor feet and the foundation.

If the motor must be mounted on steel, all supports must be of adequate size and strength and braced to assure maximum rigidity. The requirement for a level base is critical [ILLUSTRATION FOR FIGURE 1 OMITTED].Usually, for a motor installation, there will be four points of mounting: One at each corner of the mounting base. Then there will be mounting requirements for the driven load. All mounting points must be on the exact same plane or the equipment will not be level. This is why a thick, rigid steel baseplate is preferred over an assembly of steel. At the very least, a steel baseplate should be used in conjunction with the steel assembly.

For large motors, you should call in a competent engineer familiar with motor foundation designs to design and supervise required foundations and support assemblies.

Mounting. A motor can be mounted in many ways, depending upon its size, weight, and use. Small motors may incorporate a rigid mount, with the frame welded directly to a steel plate formed to match the shape of the frame and incorporating mounting holes.

Most commonly, medium- and large-size motors have mounting feet cast integrally with their frames. Vertical motors require an end bell specially machined to receive a mounting flange. Where it's important to isolate vibration and noise or to reduce the shock of starting and stopping, various types of resilient mounts and cushion bases are available.

After aligning the motor with the load, you can bolt the motor in place with maximum size bolts. It's advisable to provide some dimensional variance in the location of the foundation bolts. This can be done by locating the bolts in a steel pipe embedded in the foundation, as shown in Fig. 2, on page 68. NEMA standards give dimensions for foot mountings and some flange mountings.

Sliding bases and adapters are available for use with T-frame motors when they replace old U-frame motors.

Make sure you check whether other components or equipment such as gears, special couplings, or pumps are to be mounted on the motor. If so, be sure space is available.

After the motor base is in place but before it is fastened, you should shim as required to level the base. Use a spirit level (check two directions at 90 degrees) to ensure that motor feet will be in one plane (base not warped) when base bolts are tightened. Then, set the motor on the base, install nuts, and tighten. Do not make a final tightening until after alignment.

Motor/load components

Drive couplings. Direct coupling (rigid, flexible, or fluid) of the motor shaft to the driven load results in a 1:1 speed ratio. Where application demands other than standard available speeds, gears or pulleys/belts may be used. Variable speeds are possible by making available several gear ratios, or pulleys with variable diameters. Chain drives may also be used where shaft center-to-center distance is too great for gears or too short for belting.

Direct-connected motors with ball or roller bearings may be coupled to the load through flexible couplings. Never install a coupling half by hammering or pressing; instead, heat the coupling to install it on the shaft. Accurate mechanical lineup is essential for successful operation. Mechanical vibration and roughness during the operation of the motor may be indications of poor alignment. In general, using a straight edge across, and a feeler gauge between coupling halves, is not sufficient. Rather, you should check the lineup with a dial indicator and checking bars connected to the motor and loaded machine shafts.

Bearings. Ball, roller, or sleeve bearings may be chosen in accordance with the apparatus involved. Antifriction bearings, including ball and roller types, reduce starting friction and take up less space on the shaft than the sleeve type. Usually, they're used for totally enclosed motors and where the motor is to be operated in various positions. Standard and severe duty bearings can be obtained to meet the application requirements.

Sleeve bearings are most common in large motors (200 hp and over). Often, these bearings may be split sleeve bearings that mount on the top and bottom half of the motor endshield. Sleeve bearings are furnished with oil reservoirs, ring oilers, sight gages, level gages, and drain provisions.

Mechanical alignment

Experience has shown that any base-mounted assembly of motor and driven load, no matter how rugged or deep in section, may twist out of alignment during shipping or moving, and that alignment by eye is ineffective. Proper alignment of direct-coupled drives can be accomplished by a dial-indicator [ILLUSTRATION FOR FIGURE 3 OMITTED], laser, or computerized instrumentation.

Angular misalignment is the amount by which the faces of the two coupling halves are out of parallel. This may be determined by mounting a dial indicator on one coupling hall with the indicator probe on the face of the other half, and then rotating both shafts together through 360 degrees to determine any variation in reading.

During this check, you must keep the shaft of a motor with endplay against its thrust shoulder and the shaft of a driven load with endplay against its thrust shoulder to prevent false readings due to shaft movements in the axial direction.

Parallel misalignment is the offset between the centerlines of the two shafts. This can be determined by mounting a dial indicator on one coupling half with the indicator probe bearing radially on the other coupling half, and then rotating both shafts together through 360 degrees.

It's essential that the motor and load be correctly aligned under actual operating temperatures and conditions. Machines that are correctly aligned at room temperature may become badly misaligned due to deformation or different thermal growth associated with temperature change. The alignment must be checked, and corrected, if necessary, after the motor and driven machine have reached their maximum temperature under load.

You should use "floating shaft couplings" or "spacer couplings" on motors where the coupling alignment cannot be accurately checked and/or maintained. Misalignments of several thousandths of an inch will result when there are relatively small changes in temperature differences in larger motors and the equipment driven.

After the alignment procedure is completed, you should give the equipment a test run to verify that the lineup gives satisfactory performance. After this is verified, the machines should be dowelled to their bedplates. Recommended dowelling is two dowels per machine, one in each of the diagonally opposite feet, with the size of the dowels approximately half the diameter of the hold-down bolts.

A machine that is correctly aligned when first installed may subsequently become misaligned due to wear, vibration, shifting of the base, settling of the foundation, thermal expansion and contraction, corrosion, etc. As such, you should recheck the alignment periodically to correct for any changes.

Electrical connections

NEMA standards and Art. 430 of the NEC provide specific electrical and mechanical installation requirements and recommendations covering motors and motor controls.

Be sure that the voltage supply to the motor meets the motor requirements. Characteristics of the supply should correlate to the motor nameplate value as follows:

* Voltage: Within 10% above or below the value stamped on the nameplate.

* Frequency: Within 5% above or below the value stamped on the nameplate.

* Voltage and frequency together: Within 10% (providing frequency above is less than 5%) above or below values stamped on the nameplate.

After you've verified that the supply voltage requirements are correct, you then can make the motor terminal connections. Stator winding connections should be made as shown on the nameplate connection diagram or in accordance with the wiring diagram attached to the inside of the conduit box cover.

Terminal connection problems are usually caused by the branch- or feeder-circuit conductor being a size that is different from that of the motor lead. Branch- or feeder-circuit wire size is normally determined in accordance with the NEC based on the motor full-load current, increased where required to limit voltage drop. The motor leads, on the other hand, are permitted a higher current-carrying capacity for a given AWG size than equivalent conductors used in branch- or feeder-circuit wiring because they are exposed to circulating air within the motor.

When connecting motor leads to branch or feeder conductors (wire-to-wire connections), use a split bolt or other type connector sized to accommodate both wire sizes together. Then insulate the connector with a covering of friction tape followed by a covering of vinyl tape. Refer to NEC Table 430-12(b) for terminal housing information for motors using wire-to-wire connections and Table 430-12(c)(1) for terminal spacing information for motors using fixed terminals.

Identify motor auxiliary devices such as space heaters or temperatures sensors, connect them to proper circuits, and insulate from motor power cables.


Standards: NEMA MG2, Safety Standards For Construction and Guide Far Selection, Installation, and Use of Electric Motors and Generators. For ordering information, call 1-202-457-8400.

EC&M books: EC&M's Practical Guide to Motors and Motor Controllers; Understanding NE Code Rules on Motors and Motor Controls (2nd Edition). To order call 1-800-543-7771; or fax 1-800-633-6219.

EC&M articles: "Protecting High-Efficiency Motor Circuits," June 1995; "Effectively Applying Premium-Efficiency Motors," March 1995; "Answering Twenty Key Questions About Premium-Efficiency Motors," October 1994; "How Loads Affect the Efficiency of Motors," August 1994; "What Makes a Motor More Efficient?" May 1994. For copies, call 1-913-967-1801.

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