Enrg 2030 Lillard Chapter 8
Motor branch circuit conductors must have an ampacity of not less than __________ of the motors full-load current.
125%
Article __________ of the National Electrical Code covers installation of motor circuits.
430
In general, each motor requires a disconnecting means that is located within sight of the motor. In sight from is defined as being visible and not more than __________ feet in distance from one another.
50
DC injection braking is a method of braking in which
DC is applied to the stator windings of an AC motor
A forward-reverse motor starter must be prevented from reversing while running in the forward rotation. What is done?
Install electrical interlocking.
Which of the following starters increases the motor voltage gradually as the motor starts?
Solid-state starter
Pushbutton interlocking of reversing motor starters utilizes
a mechanical link between the forward and reverse pushbuttons.
Limit switches are used in motor control applications
all of these
Which of the following is an example of a motor controller?
all of these
Due to the operation of the centrifugal switch, the single-phase capacitor start motor must be allowed to slow down before attempting to reverse the direction of rotation.
centrifugal
The speed of wound rotor induction motor is varied by
connecting variable resistance into the rotor circuit.
Multispeed motors are available in two basic versions: consequent pole and separate winding.
consequent, separate
A motor controller is used to start and stop an electric motor by closing and opening the main power current to the motor.
controller
Which of the following soft-start acceleration modes of operation regulates the maximum staring current to some preset value?
current limit start
Which of the following does a motor starter insert into the stator winding of an AC induction motor in order to achieve frictionless braking?
dc current
The purpose of a motor disconnecting means is to open the supply conductors to the motor, allowing personal to work safely on the installation.
disconnecting wrong- disconnect
Open transition wye-delta starters
do not apply voltage to the motor during transition.
Electromechanical friction brakes rely on fiction between a __________ and __________ brake arrangement.
drum, shoe
Part-winding reduced voltage starters are used on 3-phase motors wound for dual voltage operation.
dual
A motor overload condition is normally caused by
excessive motor load
A reversing 3-phase starter requires only one contactor.
f
All motors tend to draw much less current during the starting period than when rotating at operating speed.
f
For any given HP motor the nameplate full-load ampere rating is the same as that given in NEC tables.
f
On a combination starter, the door can be opened while the disconnecting means is closed.
f
Part-winding starters are designed to start the motor by energizing both sets of windings on starting and then disconnecting one set when the motor nears operating speed.
f
Plugging produces less heat in both the motor and starter than allowing a motor to coast to a stop.
f
The acceleration of a motor when unloaded is known as jogging.
f
The full-load current rating shown on the motor's nameplate is permitted to be used to determine the ampacity of the conductors.
f
The higher the rotor resistance of a wound rotor motor, the higher the speed of the motor.
f
Wye-delta starters can be used with motors where three or six leads of the stator winding are available.
f
Manual starters can be operated on/off by remotely located control devices.
false
The starting current of a motor is approximately the same as its rated full-load current.
false
The speed of an induction motor depends on the
frequency of the power supply and number of poles built into the motor
Which of the following braking systems can hold a motor stationary once it has stopped?
friction brake
Dynamic braking is achieved by reconnecting a rotating motor to act as a generator immediately after it is turned off.
generator
Where one side of the motor control circuit is grounded, the design of the control circuit must prevent the motor from being started due to a ground fault in the control circuit wiring.
ground
The soft starter is a reduced voltage starter that restricts starting current by applying the line voltage
in a ramp.
What type of contact is an emergency stop button?
latching, nc
The current that flows before a motor begins to turn is called its
locked rotor current
A reversing starter requires __________ set(s) of overload relays.
one
Which of the following braking systems applies to stopping a motor by reversing it while it is still running in the forward direction?
plugging
In a three-phase reversing starter, the forward and reverse contactors are mechanically interlocked to
prevent a short circuit from being created across the lines
In the majority of applications motor overcurrent protection is provided by an overload __________ in the motor controller.
relay
A __________ starter is required when a motor is to be brought to a stop by means of plugging.
reversing
A zero speed or plugging switch prevents the motor from reversing after is has come to a stop.
reversing
The reversal of a DC motor is accomplished by
reversing the direction of the field current or the armature current, but not both
The reversing starter for a single-phase capacitor start motor changes the direction of rotation by interchanging the start winding leads, while those of the run winding remain the same.
start
A wound rotor induction motor has a stator like the squirrel cage motor, but a rotor with windings brought out via slip rings and brushes.
stator, rotor
With pushbutton interlocking the normally closed contact on the reverse pushbutton acts like another stop pushbutton in the forward circuit.
stop
The most common method of stopping a motor is to remove the supply voltage and allow the motor to coast to a stop.
supply
A variable frequency drive has all the features of soft starter.
t
An across-the-line starter is designed to apply full line voltage to the motor upon starting.
t
An isolation switch should not be operated under load.
t
Interchanging any two line leads to a three-phase induction motor will reverse its direction of rotation.
t
Soft-start motor starters limit motor starting current by gradually increasing the voltage applied to the motor during the starting.
t
The full-load current rating shown on the motor's nameplate is permitted to be used to determine the overload protection for the motor.
t
Time-delay fuses provide both overload and short circuit protection.
t
With an inverse time-delay circuit breaker the higher the overcurrent, the shorter the time required for the breaker to trip.
t
When utilizing jogging control
the maintaining contact must not be connected
Motor control circuits can be the same voltage as the motor up to 600 volts or can be reduced by means of a control transformer .
transformer
A single speed motor has one rated speed at which it runs when supplied with the nameplate voltage and frequency.
true
The disconnecting means for the motor controller and the motor must open all ungrounded supply conductors simultaneously.
ungrounded
Wye-delta starting involves connecting the motor windings in a wye configuration during the starting period and then in delta after the motor has begun to accelerate.
wye delta
