Questions and Answers
A sleeve bearing would typically be used in a motor that operates with a _____
light load and where noise is a factor
The width of a drive belt is classified as ______.
A or B
A direct-drive motor is usually connected to a load with a ______.
coupling
When referring to motors, to what does the 'insulation class' relate?
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The alignment of a motor and the driven mechanism must be done at room temperature and _______.
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Which of the following voltages are not safe for a 208-V motor to operate?
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The locked-rotor amperage is normally _______ times as great as the run-load amperage.
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The voltage tolerance of a standard electric motor is ______.
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The motor that should be used in a potentially wet area is a(n) ______ motor.
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If the voltage supplied to the motor is well below the motor rated voltage, the current draw will be _______ it should be.
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A slotted screw at the bottom of the bearing housing is called a _______.
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Grounding straps are required on resilient mounted motors to ______.
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Why are explosion-proof motors not normally used on standard equipment?
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A drip-proof motor is designed to prevent any lubricating oil from leaving any of the bearings.
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One method a technician can employ to check the motor is to take amperage readings of a motor (both on start-up and after start-up) and compare them to the motor's nameplate.
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There is a definite relationship between the speed of the motor and the speed of the blower.
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A motor can burn out if the supply voltage is either too high or too low.
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Regardless of the type of motor application, the motor bearings require yearly lubrication.
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The delta transformer has been popular in some locations in the past.
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When oiling a permanently lubricated motor, a 20-weight, non detergent motor oil should be used.
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Whenever possible, when changing a motor, the ___________ should be obtained.
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If the applied voltage is too high, the motor may develop local hot spots within its windings, but it will not always experience ______.
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In order to be electrically safe, a motor that is set in a 'resilient' mount must have a(n) __________.
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The vertical condenser fan is trying to fly downward into the unit to push air out the top, which puts a real load on the end of the bearing, called the ________ surface.
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The alternating current frequency supplied by the power companies in the United States is ______ hertz.
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The device that transfers the motor's energy to the driven component is called the ________.
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Name four basic methods for mounting motors.
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Explain the difference between a 'rigid' mount and a 'resilient' rubber motor mount.
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When servicing and lubricating a motor, why must a technician use the proper oil?
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Explain how a technician can verify that a motor is operating within the nameplate parameters.
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What is the major advantage of a ball bearing motor over the sleeve bearing motor?
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Study Notes
Motor Components and Categories
- Sleeve bearings are ideal for motors under light loads and where noise reduction is necessary.
- Drive belt width classification includes options A or B.
- Direct-drive motors connect to loads using couplings.
- Insulation classes for motors indicate the standard operating temperature limits.
Installation and Safety
- Motor and driven mechanism alignment must occur at room temperature along with operating temperatures.
- Safety for a 208-V motor excludes certain voltages, specifically options a and c.
- Locked-rotor amperage is typically five times greater than the run-load amperage.
Electrical Characteristics
- Standard electric motors have a voltage tolerance of +10% to -10%.
- Drip-proof motors are suitable for potentially wet environments.
- Insufficient voltage results in a current draw higher than expected.
Maintenance and Lubrication
- Relief plugs, characterized by slotted screws, facilitate maintenance of bearing housings.
- Grounding straps are essential for resilient mounted motors to protect against winding failures.
- Explosion-proof motors are avoided in standard settings due to high costs.
Truth Statements
- Drip-proof motors do not guarantee that lubricating oil remains within all bearings.
- Amperage readings taken upon startup can validate motor function by matching them to nameplate specifications.
- There is a direct correlation between motor speed and blower speed.
- Motors risk burnout from both excessively high and low supply voltage conditions.
- Yearly lubrication for motor bearings is not universally necessary.
Additional Concepts
- Delta transformers have had historical use in certain areas.
- Permanently lubricated motors should not be oiled with 20-weight non-detergent motor oil.
- Replacing a motor should ideally involve sourcing an identical model.
- Excessive voltage can cause local hot spots in windings without always leading to high amperage.
- A grounding strap is crucial for electrical safety in resilient mounts.
Mechanical Considerations
- The thrust surface in vertical condenser fans is challenged by downward airflow pushing against bearings.
- Electrical supply frequency for alternating current in the U.S. is 60 hertz.
- The drive component transmits motor energy to the driven element.
Mounting Techniques
- Basic motor mounting methods include rigid, resilient, belly band, end, and cradle mounts.
- Rigid mounts feature metal-to-metal attachment, while resilient mounts are electrically isolated by rubber.
Oil Selection
- Proper oil consistency is critical for motor operation; oil that is too thick may not turn, while too thin oil will run off.
Operational Verification
- Technicians can confirm motor efficiency by comparing operational amperage to the locked-rotor amperage on the motor's nameplate.
Bearing Comparisons
- Ball bearing motors outperform sleeve bearing motors in load capacity, whereas sleeve bearings are more suited to lighter applications with noise concerns.
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Description
Test your knowledge of motor technology with this Unit 18 quiz. The quiz covers essential concepts such as sleeve bearings, drive belt classifications, and direct-drive motor connections. Perfect for students looking to solidify their understanding of mechanical motors.
