Motor Installation
The best motors on the market will not operate properly if they are in stalled incorrectly. Therefore, all personnel involved with the installation of electric motors should thoroughly understand the proper procedures for installing the various types of motors that will be used. Furthermore, proper maintenance of each motor is essential to keep it functioning prop erly once it is installed.
When an electric motor is received from the manufacturer or sup plier, always refer to the manufacturer’s instructions and follow them to the letter. Failure to do so could result in serious injury or fatality. In general, disconnect all power before servicing. Install and ground accord ing to the NE Code and all local codes. Consult qualified personnel with any questions or services required.
UNCRATING
Once the motor has been carefully uncrated, check to see if any damage has occurred during handling. Be sure that the motor shaft and armature turn freely. This time is also a good time to check to determine if the motor has been exposed to dirt, grease, grit, or excessive moisture in either shipment or storage before installation. Motors in storage should have shafts turned over once each month to redistribute grease in the bearings.
Never start a motor which has been wet without having it thor oughly dried.
The measure of insulation resistance is a good dampness test. Clean the motor of any dirt or grit.
SAFETY
Eyebolts or lifting lugs on motors are intended only for lifting the motor and factory motor-mounted standard accessories. These lifting provi sions should never be used when lifting or handling the motor and other equipment such as pumps, gear boxes, fans, or other driven equipment as a single unit.
The eyebolt lifting capacity rating is based on a lifting alignment coincident with the eyebolt centerline. The eyebolt capacity reduces as deviation from this alignment increases.
All motors should be installed, protected, and fused in accordance with the latest issue of the NE Code, NEMA Standard Publication No.
MG-2, and any and all local requirements.
Frames and accessories of motors should be grounded in accordance with the NE Code, Article 430. For general information on grounding, refer to the NE Code, Article 250.
Rotating parts such as pulleys, couplings, external fans, and unus ual shaft extensions should be permanently guarded against accidental contact with clothing or body extremities.
THERMAL PROTECTOR INFORMATION
A space on a nameplate will be stamped or not be stamped to indicate the following:
1. The motor is thermally protected.
2. The motor is not thermally protected.
3. The motor has an overheat protective device.
For examples, refer to the following paragraphs:
1. Motors equipped with built-in thermal protection have thermally protected stamped on the nameplate. Thermal protectors open the motor circuit electrically when the motor overheats or is overloaded. The protector cannot be reset until the motor cools. If the protector is automatic, it will reset itself. If the protector is manual, press the red button to reset.
2. Motors without thermal protection have nothing stamped on the nameplate about thermal protection.
3. For motors that are provided with an overheat protective device that does not open the motor circuit directly the nameplate will be stamped with overheat protective device.
a. Motors with this type of overheat protective device have protector leads brought out in the motor conduit box marked P1 and P2 . These leads are intended for connection in series with the stop button of a three-wire pilot circuit of a magnetic controller to a motor, as in Fig. 13-1.
b. The load controlled by the preceding overheat protective device cannot exceed the values shown in the following table:
|
ac Volts |
Volt-amp Ratings |
ac Volts |
Volt-amp Ratings |
|
120 |
360 |
208 |
360 |
|
240 |
360 |
480 |
360 |
|
600 |
360 |
LOCATION
In selecting a location for the unit, first consideration should be given to ventilation. It should be far enough from walls or other objects to permit a free passage of air.
The motor should never be placed in a room with a hazardous pro
cess or where flammable gasses or combustible material may be present unless it is specifically designed for this type of service.
1. Drip-proof motors are intended for use where the atmosphere is relatively clean, dry, and noncorrosive. If the atmosphere is not like the preceding, then request approval of the motor for the use in tended.
2. Totally enclosed motors may be installed where dirt, moisture, and corrosion are present or in outdoor locations.
3. Explosion-proof motors are built for use in hazardous locations as indicated by the Underwriters’ label on the motor. Consult your local governmental inspection agency for guidance.
The ambient temperature of the air surrounding the motor should not exceed 40°C or 104°F unless the motor has been especially designed for high-ambient-temperature applications. The free flow of air around the motor should not be obstructed.
After a location has been decided upon, the mounting follows. For floor mounting, motors should be provided with a firm, rigid foundation, with the plane of four mounting stud pads flat within .010 in. for a 56 to 210 frame and .015 in. for a 250 to 680 frame. This may be accomplished by shims under the motor feet.
MOTOR DRIVES
Before connecting the motor to the load by a belt drive or direct coupling, verify manually that the rotor turns freely and does not rub.
V-BELT DRIVE.
1. Align the sheaves carefully to avoid axial thrust on the motor bearing. The drive sheave on the motor should be centered on the shaft extension.
2. Adjust the tension just enough to prevent excessive bow of the slack side.
3. If possible, make the lower side of the belt the driving side.
4. The pulley ratio should not exceed 8 to 1 or as approved by the manufacturer for a specific application.
5. Sheaves should be in accordance with NEMA Spec. MG-1.
DIRECT-CONNECTED DRIVE. Flexible or solid shaft couplings must be properly aligned for satisfactory operation. On flexible cou plings, the clearance between the ends of the shafts should be in accor
dance with the coupling manufacturer’s recommendations or NEMA standards for end play and limited travel in coupling.
Angular misalignment and run-out between direct-connected shafts will cause increased bearing loads and vibration even when the connec tion is made by means of a flexible coupling.
To check for angular misalignment, clamp the dial indicator to one coupling hub and place the finger or button of the indicator against the finished face of the other hub as shown in Fig. 13-2(a). Set the dial at zero.
Rotate one shaft, keeping the indicator button at the reference mark on the coupling hub, and note the reading on the indicator dial at each revolution.
Angular misalignment of the shafts must not exceed a total indi cator reading of .002 in. for each inch of diameter of the coupling hub.
After the shafts have been checked for angular misalignment and are parallel within the limits specified in the preceding paragraph, check the shaft for run-out to assure concentricity of the shafts. Clamp the indi cator button on the machined diameter of the other hub as shown in Fig. 13 2(b). Set the dial at zero.
Rotate one shaft, keeping the indicator button at the reference mark on the hub, and note the reading on the indicator dial at each revolution.
Total run-out between the hubs should not exceed .002 in.
Rotating parts such as couplings, external fans, and unusual shaft extensions should be permanently guarded against accidental contact with clothing or body extremities.
ELECTRICAL CONNECTIONS
All wiring, fusing, and grounding must comply with the NE Code and local requirements.
To determine proper wiring, rotations and voltage connections, refer to the information and diagram on the nameplate, separate connection plate, or decal. If the plate or decal has been removed, make inquiries of the manufacturer.
Use the proper size of line current protection and motor controls as required by the NE Code and local codes. Recommended use is 125% of full-load amps as shown on the nameplate for motors with 40°C ambient and a service factor over 1.0. Recommended use is 115% of full-load amps as shown on the nameplate for all other motors. Do not use protection with capacities larger than recommended. All three-phase motors must have all three phases protected.
CHANGING ROTATION
Before a motor may be used as a power source for equipment, the rotation sequence of both the motor and the driven unit must be determined. Rotation may be checked by jogging or bumping by applying power to the motor leads for a very short period of time-enough to just get the motor shaft to rotate a slight amount to enable observation of the shaft rotating direction.
The rotation may be changed on three-phase motors by interchang ing any two of the line leads with the motor lead connections.
PART WINDING STARTING
On those motors used for part winding starting, the elapsed time on the first step should be kept as short as possible and should not exceed 5 s. It is recommended that this time be limited to 2 s.
OPERATION
BEFORE INITIAL STARTING. The following should be checked before a motor is first started:
If a motor has become damp in shipment or in storage, it is ad visable to measure the insulation resistance of the stator winding. This value should be approximately
1. If insulation resistance is low, dry out the moisture in one of the following ways:
a. Bake in an oven at a temperature of not more than 90°C (194 °F) until the insulation resistance is practically constant.
Enclose the motor with canvas or a similar covering, leaving a hole at the top for moisture to escape, and insert the heat ing units or lamps.
a. Pass a current at low voltage (rotor-locked) through the stator winding. Increase the current gradually until the wind ing temperature, measured with a thermometer, reaches 90°C ( 194oF). Do not exceed this temperature.
2. See that the voltage and frequency stamped on the motor and the control nameplates correspond with that of the power line.
3. Check all connections to the motor and control with the wiring diagram.
5. Be sure the rotor turns freely and does not rub when discon nected from the load. Any foreign matter in the air gap should be removed.
6. Leave the motor disconnected from the load for the initial start; it is desirable to operate the motor without load for about 1h to test for any localized heating in the bearings and windings. Check for proper rotation.
COLLECTOR RINGS (WOUND ROTOR MOTORS ONLY). The collector rings are sometimes slushed at the factory to protect them while in stock and during shipment. Before putting the motor into service, the slushing should be removed with carbon tetrachloride or some other cleaning fluid that will not attack insulation, the rings should be polished with fine sandpaper, and the brushes should be set down on the collector surface. Keep the rings clean and maintain their polished surfaces. Ordi narily, the rings will require only occasional wiping with a piece of canvas or nonlinting cloth. Do not let dust or dirt accumulate between the collec tor rings.
BRUSHES (WOUND ROTOR MOTORS ONLY). See that the brushes move freely in the holders and at the same time make firm, even contact with the collector rings. The pressure should be between 2 and 3 psi of brush surface.
When installing new brushes, fit them carefully to the collectorrings. Be sure that the copper pigtail conductors are securely fastened to, and make good contact with, the brush holders.
ALLOWABLE VOLTAGE AND FREQUENCY RANGE. If the voltage and frequency are within the following range, motors will operate but with somewhat different characteristics than obtained with correct nameplate values:
1. Voltage: Within 10o/o above or below the value stamped on the nameplate
2. Frequency: Within 5o/o above or below the value stamped on the nameplate
3. Voltage and frequency together: Within lOo/o (providing the pre ceding frequency is less than 5o/o) above or below values stamped on the nameplate.
It is of absolute importance to keep both the interior and exterior of the motor free from dirt, water, oil, and grease. Motors operating in dirty places should be periodically disassembled and thoroughly cleaned.
If the motor is totally enclosed, fan-cooled, or nonventilated and is equipped with automatic drain plugs, the plugs should be free of oil, grease, paint, grit, and dirt so they do not clog up.