Achr131 Module Final Review
Possible Multiple Choice Questions
Questions and Answers
- 1.
A split-phase has a _____ winding and a _____winding.
- A.
Start, run
- B.
Start, common
- C.
Common, run
- D.
Run, common
Correct Answer
A. Start, runExplanation
In a split-phase motor, the start winding is responsible for providing the initial torque to start the motor, while the run winding is responsible for providing continuous torque to keep the motor running. Therefore, the correct answer is "start, run".Rate this question:
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- 2.
A split-phase motor can use a _____to energize and de-energize the start winding.
- A.
Potential relay
- B.
Current relay
- C.
Centrifugal switch
- D.
All of the above
Correct Answer
D. All of the aboveExplanation
A split-phase motor can use all of the above options (potential relay, current relay, centrifugal switch) to energize and de-energize the start winding. These components are commonly used in split-phase motors to control the starting and running of the motor. The potential relay senses the voltage across the start winding and switches it on or off accordingly. The current relay monitors the current flowing through the start winding and controls its activation. The centrifugal switch is activated by the motor's rotational speed and helps to disconnect the start winding once the motor reaches a certain speed.Rate this question:
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- 3.
A current magnetic relay opens and closes its contacts based on the _____.
- A.
Current in the start winding
- B.
Voltage across the start winding
- C.
Voltage across the run winding
- D.
Current in the run winding
Correct Answer
D. Current in the run windingExplanation
The current magnetic relay opens and closes its contacts based on the current in the run winding. This means that the relay is designed to respond to the flow of electrical current in the run winding of the device it is connected to. When the current exceeds a certain threshold, the relay will open or close its contacts, allowing or interrupting the flow of electricity to other components in the circuit.Rate this question:
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- 4.
A permanent split capacitor (PSC) motor that is running and up to speed will have the start winding _____ .
- A.
Energized
- B.
De-energized
- C.
In series with the run winding
- D.
Removed from the circuit
Correct Answer
A. EnergizedExplanation
When a permanent split capacitor (PSC) motor is running and up to speed, the start winding will remain energized. This means that the start winding will still receive electrical power and be active while the motor is running. The start winding is responsible for providing the initial torque to start the motor, and once the motor reaches its operating speed, it continues to be energized to maintain the motor's performance.Rate this question:
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- 5.
A split-phase motor that has a current relay and a start capacitor is called a _____motor.
- A.
Capacitor Start, Capacitor Run (CSCR)
- B.
Capacitor Start, Induction Run (CSIR)
- C.
Induction Start, Induction Run (ISIR)
- D.
Permanent Split Capacitor (PSC)
Correct Answer
B. Capacitor Start, Induction Run (CSIR)Explanation
A split-phase motor that has a current relay and a start capacitor is called a Capacitor Start, Induction Run (CSIR) motor. In this type of motor, the start winding is connected to both the main winding and a start capacitor. The start capacitor provides an initial phase shift to the start winding, creating a rotating magnetic field. Once the motor reaches a certain speed, the current relay disconnects the start winding and capacitor, and the motor continues to run on the main winding alone. This design allows for high starting torque while still maintaining efficient operation.Rate this question:
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- 6.
When a Capacitor Start, Capacitor Run (CSCR) motor initially starts, what is the total capacitance acting on the motor? (Assume the run capacitor is 5 microfarads and the start capacitor is 20 microfarads.)
- A.
5 microfarads
- B.
4 microfarads
- C.
20 microfarads
- D.
25 microfarads
Correct Answer
D. 25 microfaradsExplanation
When a Capacitor Start, Capacitor Run (CSCR) motor initially starts, the total capacitance acting on the motor is the sum of the capacitance of the run capacitor and the start capacitor. In this case, the run capacitor is 5 microfarads and the start capacitor is 20 microfarads, so the total capacitance is 25 microfarads.Rate this question:
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- 7.
When a Capacitor Start Induction Run (CSIR) motor is running and up to speed, what is the total capacitance acting on the motor? (Assume the run capacitor is 5 microfarads and the start capacitor is 20 microfarads.)
- A.
4 microfarads
- B.
5 microfarads
- C.
20 microfarads
- D.
25 microfarads
Correct Answer
B. 5 microfaradsExplanation
The total capacitance acting on the motor when it is running and up to speed is 5 microfarads. This is because the run capacitor, which has a capacitance of 5 microfarads, is the only capacitor that remains in the circuit during normal operation. The start capacitor, which has a capacitance of 20 microfarads, is only used during the starting phase of the motor and is disconnected once the motor reaches its operating speed. Therefore, the total capacitance acting on the motor is equal to the capacitance of the run capacitor, which is 5 microfarads.Rate this question:
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- 8.
The starting device usually used on single phase, fractional horsepower compressor motors is the _____.
- A.
Potential relay
- B.
Current relay
- C.
Centrifugal switch
- D.
None of the above
Correct Answer
B. Current relayExplanation
A current relay is typically used as the starting device for single-phase, fractional horsepower compressor motors. It is responsible for controlling the flow of current to the motor, ensuring that it starts smoothly and efficiently. The current relay senses the current passing through the motor and activates the necessary components to start the motor. This type of relay is commonly used in small motors where a potential relay or centrifugal switch may not be suitable or necessary.Rate this question:
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- 9.
A motor's speed is determined by _____.
- A.
Size
- B.
Voltage
- C.
Amperage
- D.
Number of motor poles
Correct Answer
D. Number of motor polesExplanation
The speed of a motor is determined by the number of motor poles. Motor poles are the magnetic poles found in the stator of the motor. The more motor poles there are, the faster the motor will rotate. This is because the number of poles directly affects the frequency of the rotating magnetic field, which in turn determines the speed of the motor. Therefore, the correct answer is the number of motor poles.Rate this question:
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- 10.
Start windings are placed _____the run windings.
- A.
Outside
- B.
Inside
- C.
Between
- D.
In series with
Correct Answer
C. BetweenExplanation
The start windings are placed between the run windings. This arrangement allows for the start windings to provide an initial boost of power to the motor during startup, helping it overcome inertia and start rotating. Once the motor reaches a certain speed, the start windings are typically disconnected, and the motor continues to run using only the run windings. Placing the start windings between the run windings allows for a more efficient and controlled startup process.Rate this question:
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- 11.
The start windings have _____.
- A.
Fewer turns than the run windings
- B.
More turns than the run windings
- C.
The same number of turns as the run windings
- D.
Larger diameter wire than the run windings
Correct Answer
B. More turns than the run windingsExplanation
The start windings have more turns than the run windings. This is because the start windings are designed to provide a higher resistance and lower current to create a rotating magnetic field to initiate the motor's rotation. The additional turns in the start windings help to generate this higher resistance and lower current, allowing the motor to start smoothly. In contrast, the run windings have fewer turns and lower resistance to maintain the motor's rotation once it has started.Rate this question:
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- 12.
When a general duty split-phase motor reaches approximately 75% of its operating speed, the start winding is de-energized by a _____.
- A.
Circuit board
- B.
Capacitor
- C.
Centrifugal switch
- D.
Dual voltage switch
Correct Answer
C. Centrifugal switchExplanation
When a general duty split-phase motor reaches approximately 75% of its operating speed, the start winding is de-energized by a centrifugal switch. This switch is typically located on the motor shaft and is activated by centrifugal force as the motor spins. Once the motor reaches a certain speed, the centrifugal switch opens, disconnecting the start winding from the power source. This is necessary to prevent damage to the motor and ensure efficient operation.Rate this question:
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- 13.
Capacitors wired in series with the starting winding provide _____.
- A.
Longer starting time
- B.
Greater starting torque
- C.
An aid in starting three phase motors
- D.
More efficient operation at full load speed
Correct Answer
B. Greater starting torqueExplanation
Capacitors wired in series with the starting winding provide greater starting torque. This is because the capacitors help to create a phase shift in the current flowing through the starting winding, which results in a rotating magnetic field. This rotating magnetic field produces a higher torque, allowing the motor to start more easily, especially under heavy loads. By increasing the starting torque, the capacitors enhance the motor's ability to overcome inertia and start the rotation.Rate this question:
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- 14.
The shaded pole motor _____.
- A.
Has little starting torque
- B.
Has excessive starting torque
- C.
Has greater efficiency than most split-phase motors
- D.
Will start against a heavy starting load
Correct Answer
A. Has little starting torqueExplanation
The shaded pole motor has little starting torque. This means that it does not have a strong initial force to overcome the resistance and start rotating.Rate this question:
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- 15.
Three phase motors have _____.
- A.
Three start and three run windings for each phase
- B.
One start and one run winding for each phase
- C.
Run windings only
- D.
A start switch in each phase circuit
Correct Answer
C. Run windings onlyExplanation
Three phase motors have run windings only. Unlike single-phase motors, which typically have both start and run windings, three-phase motors do not require separate start windings. This is because the rotating magnetic field created by the three-phase power supply provides the necessary torque to start the motor. The run windings are responsible for maintaining the motor's rotation once it is started.Rate this question:
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- 16.
The positive-temperature-coefficient start device is a type of _____.
- A.
Capacitor
- B.
Thermistor
- C.
Switching device
- D.
Diode
Correct Answer
B. ThermistorExplanation
A positive-temperature-coefficient start device refers to a thermistor. A thermistor is a type of resistor whose resistance increases with an increase in temperature. In the context of a start device, this thermistor is used to provide a higher resistance at startup, limiting the current flow and protecting the device from excessive current. As the temperature increases during operation, the resistance of the thermistor decreases, allowing for normal operation. Therefore, a thermistor is the correct answer for the given question.Rate this question:
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- 17.
A permanent split-capacitor motor has a _____.
- A.
Start and run capacitor
- B.
Start capacitor only
- C.
Run capacitor only
- D.
Split phase capacitor
Correct Answer
C. Run capacitor onlyExplanation
A permanent split-capacitor motor only has a run capacitor. This type of motor uses a single winding with two separate windings that are connected in parallel. The run capacitor is used to create a phase shift in the current, which helps to start and run the motor smoothly. It provides the necessary torque and helps to maintain a steady speed during operation. Unlike other types of motors, a permanent split-capacitor motor does not require a start capacitor as it is designed to start on its own with the help of the run capacitor.Rate this question:
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- 18.
When referring to motors, to what does the "insulation class" relate?
- A.
The noise level of the motor
- B.
The type of base on which the motor is mounted
- C.
The normal operating temperature of the motor
- D.
Both a and b
Correct Answer
C. The normal operating temperature of the motorExplanation
The "insulation class" of a motor refers to the normal operating temperature of the motor. This means that the insulation class indicates the maximum temperature that the motor's insulation can withstand without degrading or causing a safety hazard. It is an important factor to consider when selecting a motor, as it ensures that the motor can operate safely and reliably within its specified temperature range. The insulation class is typically designated by a letter, such as F or H, which corresponds to a specific temperature rating.Rate this question:
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- 19.
Why are explosion-proof motors not normally used on standard equipment?
- A.
They are too large.
- B.
They are too noisy.
- C.
They are too expensive.
- D.
They cannot be replaced.
Correct Answer
C. They are too expensive.Explanation
Explosion-proof motors are not normally used on standard equipment because they are too expensive. This implies that the cost of these motors is significantly higher compared to other types of motors, making them impractical for regular use. The other options provided, such as being too large, too noisy, or unable to be replaced, do not explain why explosion-proof motors are not used on standard equipment.Rate this question:
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- 20.
The motor that should be used in a potentially wet area is a(n) _____motor.
- A.
Enclosed
- B.
Drip proof
- C.
Explosion proof
- D.
Open
Correct Answer
B. Drip proofExplanation
A drip proof motor is designed to prevent water from entering the motor enclosure when water is dripping or splashing on it. It has additional protection measures such as shields or covers to ensure that water does not come into contact with the internal components of the motor. Therefore, a drip proof motor would be the appropriate choice for a potentially wet area to prevent any damage or malfunction caused by water exposure.Rate this question:
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- 21.
Which of the following voltages are not safe for a 208-V motor to operate?
- A.
170 volts
- B.
220 volts
- C.
238 volts
- D.
Both a and c
Correct Answer
D. Both a and cExplanation
Both 170 volts and 238 volts are not safe for a 208-V motor to operate because they are outside the acceptable voltage range. The motor is designed to operate at 208 volts, so any voltage lower than this (such as 170 volts) or higher than this (such as 238 volts) can potentially damage the motor or cause it to malfunction. Therefore, both options a and c are not safe for the motor to operate.Rate this question:
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- 22.
A sleeve bearing would typically be used in a motor that operates with a _____.
- A.
Light load and where noise is a factor
- B.
Heavy load and where noise is a factor
- C.
Heavy load in a dirty atmosphere
- D.
Heavy load in a moist atmosphere
Correct Answer
A. Light load and where noise is a factorExplanation
A sleeve bearing is a type of bearing that is suitable for applications with light loads and where noise is a factor. Sleeve bearings are designed to provide low friction and smooth operation, making them ideal for situations where noise reduction is important. Additionally, they are not as durable as other types of bearings and may not be able to withstand heavy loads or harsh environments. Therefore, they are best suited for motors that operate with light loads and where noise reduction is a priority.Rate this question:
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- 23.
If the voltage supplied to the motor is well below the motor rated voltage, the current draw will be _____it should be.
- A.
Lower than
- B.
The same as
- C.
Higher than
- D.
In reverse polarity than
Correct Answer
C. Higher thanExplanation
If the voltage supplied to the motor is well below the motor rated voltage, it means that the motor is not receiving enough voltage to operate at its full capacity. In this situation, the motor will try to compensate for the low voltage by drawing more current from the power source. Therefore, the current draw will be higher than it should be in order to try and maintain the motor's performance.Rate this question:
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- 24.
The voltage tolerance of a standard electric motor is _____.
- A.
+10% -5%
- B.
+5% -10%
- C.
+10% -10%
- D.
+15% -15%
Correct Answer
C. +10% -10%Explanation
The voltage tolerance of a standard electric motor is +10% -10%. This means that the motor can operate safely and efficiently within a range of voltage that is 10% above or 10% below its rated voltage. This tolerance allows for variations in the power supply and ensures that the motor can handle fluctuations in voltage without being damaged.Rate this question:
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- 25.
The locked-rotor amperage is normally _____times as great as the run-load amperage.
- A.
Two
- B.
Three
- C.
Five
- D.
Ten
Correct Answer
C. FiveExplanation
The locked-rotor amperage refers to the current drawn by a motor when it is initially started and the rotor is not moving. This current is typically much higher than the run-load amperage, which is the current drawn by the motor when it is operating under normal conditions. In this case, the locked-rotor amperage is five times greater than the run-load amperage.Rate this question:
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- 26.
A direct-drive motor is usually connected to a load with a _____.
- A.
Cradle mount
- B.
Rigid base mount
- C.
Pulley
- D.
Coupling
Correct Answer
D. CouplingExplanation
A direct-drive motor is usually connected to a load with a coupling. A coupling is a device that connects two shafts together to transmit power. It allows for the transfer of torque from the motor to the load while accommodating any misalignment or slight movement between the two components. Couplings are commonly used in direct-drive systems to ensure efficient power transmission and smooth operation.Rate this question:
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- 27.
The width of a drive belt is classified as _____.
- A.
Large or small
- B.
Narrow or wide
- C.
A or B
- D.
1 or 2
Correct Answer
C. A or BExplanation
The width of a drive belt can be classified as either large or small, or alternatively as narrow or wide. Both options A and B are correct ways to classify the width of a drive belt.Rate this question:
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- 28.
An instrument often used to check the alignment of two shafts is the _____.
- A.
Micronometer
- B.
Dial indicator
- C.
Monometer
- D.
Sling psychrometer
Correct Answer
B. Dial indicatorExplanation
A dial indicator is often used to check the alignment of two shafts. It is a precision measuring tool that has a dial face with a needle that moves in response to small changes in distance. By placing the dial indicator against the shafts, any misalignment or deviation can be detected and measured. This allows for adjustments to be made to ensure proper alignment and prevent any potential issues or damage. A micronometer, monometer, and sling psychrometer are not typically used for this purpose.Rate this question:
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- 29.
A slotted screw at the bottom of the bearing housing is called a _____.
- A.
Drain plug
- B.
Purge screw
- C.
Relief plug
- D.
Retaining screw
Correct Answer
C. Relief plugExplanation
A slotted screw at the bottom of the bearing housing is called a relief plug. This type of screw is commonly used to release pressure or relieve excess fluid from the bearing housing. It allows for the drainage of any built-up fluid or the release of pressure to prevent damage to the bearing. The relief plug serves as a safety feature to maintain the proper functioning and longevity of the bearing.Rate this question:
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- 30.
Grounding straps are required on resilient mounted motors to _____.
- A.
Prevent rotation of the motor in the mount
- B.
Help reduce motor vibration transfer to the object on which the motor is mounted
- C.
Ground the motor in case of winding failure
- D.
Act as the position for locating the motor leads
Correct Answer
C. Ground the motor in case of winding failureExplanation
Grounding straps are required on resilient mounted motors to ground the motor in case of winding failure. In the event of a winding failure, the grounding strap provides a path for the electrical current to flow safely to the ground, preventing any potential electrical hazards. This helps protect both the motor and the surrounding equipment or objects from damage or malfunction caused by electrical faults.Rate this question:
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- 31.
When a contractor's coil is energized, how much resistance should be measured between terminal "L1" and terminal "T1"?
- A.
Zero ohms
- B.
50-3000 ohms
- C.
5000-6000 ohms
- D.
Infinite
Correct Answer
A. Zero ohmsExplanation
When a contractor's coil is energized, there should be zero ohms of resistance measured between terminal "L1" and terminal "T1". This indicates that there is a direct connection between the two terminals, allowing the current to flow freely without any obstruction. The absence of resistance ensures efficient operation of the contractor.Rate this question:
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- 32.
Technician "A" says that if you take a voltage reading from terminal "L1" to terminal "T1" on a contactor whose coil is energized, you should read zero volts. Technician "B" says that contactors can only have normally open contacts. Which of the following statements is correct?
- A.
Technician "A" is correct. Technician "B" is correct.
- B.
Technician "A" is correct. Technician "B" is incorrect.
- C.
Technician "A" is incorrect. Technician "B" is correct.
- D.
Technician "A" is incorrect. Technician "B" is incorrect.
Correct Answer
B. Technician "A" is correct. Technician "B" is incorrect.Explanation
Technician "A" is correct because when the coil of a contactor is energized, it closes the contacts and allows current to flow through. Therefore, taking a voltage reading from terminal "L1" to terminal "T1" should show zero volts, as there should be no potential difference between these two terminals. Technician "B" is incorrect because contactors can have both normally open and normally closed contacts, depending on their design and purpose.Rate this question:
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- 33.
An inherent motor protector is a _____ .
- A.
Circuit breaker
- B.
Motor starter overload
- C.
Thermally activated device in the motor winding
- D.
Line fuse
Correct Answer
C. Thermally activated device in the motor windingExplanation
An inherent motor protector is a thermally activated device in the motor winding. This device is designed to protect the motor from overheating by sensing the temperature of the motor winding. If the temperature exceeds a certain threshold, the protector will automatically disconnect the motor from the power source, preventing any damage to the motor. This helps to ensure the safe and efficient operation of the motor.Rate this question:
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- 34.
The service factor of an electric motor is determined by _____.
- A.
National Electrical Code
- B.
National Electrical Manufacturers Association code
- C.
Motor's reserve capacity
- D.
The required wire size supplying power to the motor
Correct Answer
C. Motor's reserve capacityExplanation
The service factor of an electric motor is determined by its reserve capacity. The reserve capacity refers to the motor's ability to handle temporary overloads or surges in power demand without overheating or causing damage. A higher reserve capacity indicates a more robust motor that can withstand higher loads and operate more reliably. The service factor is typically expressed as a decimal or a percentage, with values above 1 indicating an increased capacity to handle overload conditions.Rate this question:
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- 35.
Which of the following overload devices is not affected by ambient temperature?
- A.
Solder pot
- B.
Magnetic
- C.
Bimetal
- D.
Time-delay fuse
Correct Answer
B. MagneticExplanation
A magnetic overload device is not affected by ambient temperature because it operates based on the magnetic field strength, rather than relying on the expansion or contraction of materials like solder pot or bimetal overload devices. The magnetic overload device uses a magnetic coil that generates a magnetic field, and when the current exceeds a certain threshold, the magnetic field pulls on a plunger or armature, causing the device to trip and disconnect the circuit. This mechanism is not influenced by changes in temperature, making it a reliable choice for overload protection in different environmental conditions.Rate this question:
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- 36.
Standards for motor overload protection are set by the _____.
- A.
United States Department of Transportation
- B.
National Electrical Code
- C.
Environmental Protection Agency
- D.
American National Standards Institute
Correct Answer
B. National Electrical CodeExplanation
The National Electrical Code (NEC) is a set of standards and regulations that govern the installation and use of electrical systems in the United States. It provides guidelines for motor overload protection, which is essential for preventing damage to motors and ensuring their safe operation. The NEC is widely recognized and followed by electricians, engineers, and other professionals in the electrical industry. It covers various aspects of electrical safety, including overload protection, grounding, wiring methods, and more. Therefore, it is the correct answer for this question.Rate this question:
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- 37.
A common practice in condensing units is to use a contactor with only one set of contacts opening only one side of the power to the unit. This is to _____.
- A.
Reduce the cost of the contactor
- B.
Make it easier to wire the unit
- C.
Teach the service technician not to put hands in the unit with the power on
- D.
Provide off-cycle heat to the compressor
Correct Answer
D. Provide off-cycle heat to the compressorExplanation
The practice of using a contactor with only one set of contacts opening only one side of the power to the unit is done to provide off-cycle heat to the compressor. This is because when the contacts open, the current flow is interrupted, causing resistance and generating heat. This heat helps to prevent the compressor from getting too cold during off-cycles, which can lead to damage or inefficiency.Rate this question:
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- 38.
Beside maintaining pressure on the contacts for current carrying capacity, the pressure springs have a second important function. This is to _____.
- A.
Keep the contacts in line
- B.
Help obtain equal contacts against the stationary contacts
- C.
Slow down the pull of the armature into place to reduce the noise
- D.
Increase the power required to close the contacts
Correct Answer
B. Help obtain equal contacts against the stationary contactsExplanation
The pressure springs help obtain equal contacts against the stationary contacts. This means that they ensure that all the contacts make equal and proper contact with the stationary contacts, which is important for the efficient flow of current. By applying pressure on the contacts, the springs help to maintain a consistent and reliable electrical connection, preventing any interruptions or fluctuations in the current flow.Rate this question:
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- 39.
What is the best method to repair a fractional horsepower motor that has bad bearings?
- A.
Replace the bearings.
- B.
Replace the bearings and shaft.
- C.
Add a capacitor to the circuit for added torque.
- D.
Replace the entire motor.
Correct Answer
D. Replace the entire motor.Explanation
The best method to repair a fractional horsepower motor with bad bearings is to replace the entire motor. This is because if the bearings are bad, it indicates that there may be other internal issues with the motor as well. Simply replacing the bearings may not fully resolve the problem and could lead to further issues down the line. Therefore, it is more efficient and effective to replace the entire motor to ensure proper functioning and avoid future breakdowns.Rate this question:
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- 40.
A technician needs to check a single-phase compressor. He labels the three terminals "A," "B," and "C" and take resistance readings of the windings. He reads 10 ohms from "A" to "B," infinity from "B" to "C," and infinity from "C" to "A." Identify the terminals.
- A.
A: common B: start C: run
- B.
Cannot identify terminals: winding grounded
- C.
A: start B: run C: common
- D.
Cannot identify terminals: open winding
Correct Answer
D. Cannot identify terminals: open windingExplanation
The technician cannot identify the terminals because there is an open winding in the compressor. This is indicated by the infinity resistance readings when measuring from B to C and from C to A. An open winding means that there is a break in the circuit, preventing current from flowing through that particular winding. Without a complete circuit, the terminals cannot be accurately identified.Rate this question:
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- 41.
Technician "A" says that a shorted winding will result in an increased current flow through the winding. Technician "B" says that if a motor is to be replaced, a motor with a lower horsepower rating should always be used. Which of the following statements is correct?
- A.
Technician "A" is correct. Technician "B" is correct.
- B.
Technician "A" is correct. Technician "B" is incorrect.
- C.
Technician "A" is incorrect. Technician "B" is correct.
- D.
Technician "A" is incorrect. Technician "B" is incorrect.
Correct Answer
B. Technician "A" is correct. Technician "B" is incorrect.Explanation
Technician "A" is correct because a shorted winding in a motor will create a low resistance path, causing an increased current flow through the winding. This increased current can lead to overheating and damage to the motor. However, Technician "B" is incorrect because when replacing a motor, a motor with the same or higher horsepower rating should be used to ensure that it can handle the same or greater workload as the original motor. Using a motor with a lower horsepower rating could result in insufficient power and poor performance.Rate this question:
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- 42.
Technician "A" says that while checking the windings of a compressor, a reading of 10 ohms or less from the common terminal to ground indicates that the motor is okay. Technician "B" says that the resistance of the start winding should always be less than the resistance of the run winding. Which of the following statements is correct?
- A.
Technician "A" is correct. Technician "B" is correct.
- B.
Technician "A" is correct. Technician "B" is incorrect.
- C.
Technician "A" is incorrect. Technician "B" is correct.
- D.
Technician "A" is incorrect. Technician "B" is incorrect.
Correct Answer
D. Technician "A" is incorrect. Technician "B" is incorrect.Explanation
Technician "A" is incorrect because a reading of 10 ohms or less from the common terminal to ground does not indicate that the motor is okay. This reading actually indicates a potential ground fault in the motor windings, which is a problem. Technician "B" is also incorrect because the resistance of the start winding does not always have to be less than the resistance of the run winding. The resistance values can vary depending on the specific motor design and specifications.Rate this question:
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- 43.
If a motor hums but does not start, there is a potential problem _____ .
- A.
With the starting components
- B.
With an open winding
- C.
With insufficient supply voltage
- D.
All of the above
Correct Answer
D. All of the aboveExplanation
If a motor hums but does not start, it indicates that there could be a potential problem with the starting components, such as a faulty capacitor or relay. It could also be due to an open winding, which means that there is a break in the wire coil inside the motor. Additionally, insufficient supply voltage can also prevent the motor from starting. Therefore, all of the above options could be potential reasons for the motor humming but not starting.Rate this question:
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- 44.
An open winding in an electric motor means that _____ .
- A.
The winding is making contact with the motor failure
- B.
One winding is making contact with another winding
- C.
A wire in a winding is broken
- D.
The centrifugal switch to the start winding is open
Correct Answer
C. A wire in a winding is brokenExplanation
In an electric motor, an open winding refers to a situation where a wire in one of the windings is broken. This break in the wire disrupts the flow of electricity and can cause the motor to malfunction or fail. It is important to identify and repair any open windings in order to restore proper functionality to the motor.Rate this question:
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- 45.
If the resistance of the run winding decreases, the _____ .
- A.
Motor probably will not start
- B.
Motor will draw too much current while it is running
- C.
Centrifugal starting switch will not start the motor
- D.
Load on the motor is probably too great
Correct Answer
B. Motor will draw too much current while it is runningExplanation
If the resistance of the run winding decreases, it means that the run winding will have less opposition to the flow of current. This will result in an increase in the current flowing through the winding. As a result, the motor will draw too much current while it is running.Rate this question:
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- 46.
The wiring and connectors that carry the power to a motor must be in good condition. When a connection becomes loose, oxidation of the copper wire occurs. The oxidation _____ .
- A.
Has no effect on the electrical connection
- B.
Acts as an electrical resistance and causes the connection to heat more
- C.
Decrease the resistance
- D.
None of the above
Correct Answer
B. Acts as an electrical resistance and causes the connection to heat moreExplanation
When oxidation occurs on the copper wire, it acts as an electrical resistance. This resistance hinders the flow of current, causing the connection to heat up more than usual. Therefore, the correct answer is that oxidation acts as an electrical resistance and causes the connection to heat more.Rate this question:
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- 47.
A megger _____ .
- A.
Is a ammeter that can measure small amounts of current
- B.
Is digital voltmeter that measures very high resistances
- C.
Measures high voltage direct current
- D.
Measures very high resistances
Correct Answer
D. Measures very high resistancesExplanation
pg.391, The megohmmeter is often called a Megger and will measure resistances in the millions of ohms.Rate this question:
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- 48.
The recommended way to discharge a capacitor is to _____ .
- A.
Place a screwdriver across the terminals
- B.
Assume it will discharge itself over a period of time
- C.
Use 20,000 ohm 5 watt resistor that has had insulated leads soldered to it
- D.
Use an ohmmeter
Correct Answer
C. Use 20,000 ohm 5 watt resistor that has had insulated leads soldered to itExplanation
The recommended way to discharge a capacitor is to use a 20,000 ohm 5 watt resistor that has had insulated leads soldered to it. This resistor will provide a controlled path for the discharge of the capacitor's stored energy, ensuring safe and gradual discharge without causing any damage or danger. Placing a screwdriver across the terminals can be dangerous as it can cause a spark or short circuit. Assuming it will discharge itself over time is not a reliable method as it may take a long time and can still pose risks. Using an ohmmeter is not suitable for discharging a capacitor as it is designed for measuring resistance, not discharging.Rate this question:
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- 49.
If a condenser fan motor grounds out, it will usually _____ .
- A.
Trip a circuit breaker to shut off the unit
- B.
Keep running as the current is only going to ground
- C.
Run a little faster because the amperage draw will increase
- D.
Cause the evaporator to ice up
Correct Answer
A. Trip a circuit breaker to shut off the unitExplanation
If a condenser fan motor grounds out, it will usually trip a circuit breaker to shut off the unit. When a motor grounds out, it means that there is an electrical connection between the motor windings and the motor casing. This causes an excessive amount of current to flow through the circuit, which can overload the circuit and cause the circuit breaker to trip. Tripping the circuit breaker is a safety mechanism to prevent further damage and potential fire hazards.Rate this question:
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- 50.
Most electrical problems with an electric motor are _____ .
- A.
Short circuited windings, closed windings, and grounded windings
- B.
Short circuited windings, open windings, and grounded windings
- C.
All of the above
- D.
None of the above
Correct Answer
B. Short circuited windings, open windings, and grounded windingsExplanation
Most electrical problems with an electric motor can be attributed to short circuited windings, open windings, and grounded windings. Short circuited windings occur when there is a connection between two or more winding turns, causing excessive current flow and overheating. Open windings refer to a break in the winding circuit, resulting in a loss of continuity and preventing the motor from functioning properly. Grounded windings happen when one or more of the windings come into contact with the motor's frame or ground, causing a short circuit and potential damage to the motor. Therefore, all of these issues can contribute to electrical problems in an electric motor.Rate this question:
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