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Questions and Answers
Any exposed live parts must be guarded if they are operating at ______
Any exposed live parts must be guarded if they are operating at ______
50v or more between terminals
Which of the following is most likely to use dynamic braking?
Which of the following is most likely to use dynamic braking?
- Pump
- Forklift (correct)
- Crane
- Elevator
In a DC series motor, how much of its full-load torque is developed at starting?
In a DC series motor, how much of its full-load torque is developed at starting?
500%
For a given number of poles, what determines the speed of an AC motor?
For a given number of poles, what determines the speed of an AC motor?
Which of the following motors is used when high starting torque and speed control is desirable?
Which of the following motors is used when high starting torque and speed control is desirable?
What is the synchronous speed at which a four-pole, 60Hz induction motor operates?
What is the synchronous speed at which a four-pole, 60Hz induction motor operates?
A typical constant-torque load would be a(an) [blank].
A typical constant-torque load would be a(an) [blank].
Horsepower is used to rate the [blank].
Horsepower is used to rate the [blank].
What is the D dimension of a medium-sized motor with a frame number of 284T?
What is the D dimension of a medium-sized motor with a frame number of 284T?
In a split-phase motor, how much greater is the starting current compared to the full-load current?
In a split-phase motor, how much greater is the starting current compared to the full-load current?
The capacitor-start motor is the single-phase motor type that has the [blank].
The capacitor-start motor is the single-phase motor type that has the [blank].
For a constant-torque load, the horsepower increases and decreases ______.
For a constant-torque load, the horsepower increases and decreases ______.
The primary method of varying the speed on a DC shunt motor is to adjust the voltage and current on the winding or the [blank].
The primary method of varying the speed on a DC shunt motor is to adjust the voltage and current on the winding or the [blank].
According to NEMA definitions, which of the following is a type of open motor?
According to NEMA definitions, which of the following is a type of open motor?
The value indicated in rpm on the nameplate is the [blank].
The value indicated in rpm on the nameplate is the [blank].
The power factor of an induction motor at no-load conditions can be as low as [blank].
The power factor of an induction motor at no-load conditions can be as low as [blank].
Which of the following motors provides constant speed from no-load conditions to full-load conditions?
Which of the following motors provides constant speed from no-load conditions to full-load conditions?
The most common service factor appearing on a motor's nameplate is [blank].
The most common service factor appearing on a motor's nameplate is [blank].
Several motors are permitted to be supplied by a single branch circuit as long as each motor is no larger than [blank].
Several motors are permitted to be supplied by a single branch circuit as long as each motor is no larger than [blank].
The stationary magnet of a DC motor is represented by the [blank].
The stationary magnet of a DC motor is represented by the [blank].
Which of the following motors is the best installation choice for an application requiring adjustable speeds?
Which of the following motors is the best installation choice for an application requiring adjustable speeds?
The speed of a three-phase squirrel cage induction motor is controlled by the frequency of the applied voltage and the [blank].
The speed of a three-phase squirrel cage induction motor is controlled by the frequency of the applied voltage and the [blank].
DC injection braking is used on the [blank].
DC injection braking is used on the [blank].
The NEC requires motor disconnecting means to be ______.
The NEC requires motor disconnecting means to be ______.
A polyphase synchronous motor has three stator windings that are [blank] apart.
A polyphase synchronous motor has three stator windings that are [blank] apart.
A three-phase induction motor may have [blank].
A three-phase induction motor may have [blank].
The terminals of a motor can be identified using a battery and a(an) [blank].
The terminals of a motor can be identified using a battery and a(an) [blank].
Which motor should be used for applications that require frequent starts without overheating the motor?
Which motor should be used for applications that require frequent starts without overheating the motor?
According to NEMA definitions, which of the following is a type of totally enclosed motor?
According to NEMA definitions, which of the following is a type of totally enclosed motor?
A delta-connected motor has [blank].
A delta-connected motor has [blank].
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Study Notes
Electrical Components and Operations
- Any exposed live parts must be guarded at voltages of 50V or more between terminals.
- DC series motors develop full-load torque at a starting rate of 500%.
- The stationary magnet in a DC motor is represented by field poles.
Motor Types and Characteristics
- Dynamic braking is most commonly used in forklifts.
- Compound motors are preferred when high starting torque and speed control are desired.
- Synchronous motors provide constant speed from no-load to full-load conditions.
Motor Performance and Ratings
- Horsepower ratings indicate the output capacity of motors.
- The rated full-load speed of a motor is denoted in rpm on the nameplate.
- The most common service factor found on a motor's nameplate is 1.15.
Motor Design Specifications
- A medium-size motor with a frame number 284T has a D dimension of 7 inches.
- A capacitor-start motor type offers the highest starting torque among single-phase motors.
- A three-phase induction motor may have 2 poles.
Speed Control and Operational Factors
- The speed of AC motors is determined by frequency and the number of poles.
- The primary method of speed variation in a DC shunt motor is through adjusting voltage and current on the armature.
- The speed of a three-phase squirrel cage induction motor is influenced by the frequency of applied voltage and the number of poles.
Electrical Safety and Standards
- The National Electrical Code (NEC) mandates that motor disconnecting means must be within sight of the controller location.
- Several motors can be supplied by a single branch circuit if each motor is no larger than 1 horsepower.
Load Characteristics
- A typical constant-torque load example is a conveyor system.
- For constant-torque loads, horsepower varies directly with speed.
- Starting current for a split-phase motor is typically 6 to 8 times greater than the full-load current.
Additional Motor Features
- DC injection braking is utilized on the stationary windings of AC motors.
- Weather-protected motors are classified as open motors according to NEMA definitions.
- Water-cooled motors are categorized as totally enclosed motors according to NEMA definitions.
Testing and Identification
- To identify motor terminals, a battery and voltmeter can be used.
- A wound rotor induction motor is suggested for applications that require frequent starts without overheating.
Special Motor Configurations
- A polyphase synchronous motor features three stator windings spaced 120 degrees apart.
- A delta-connected motor configuration consists of 9 leads.
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