Chapter 10 Flashcards
Article ____________ of the National Electrical Code covers installation of motor circuits.
430
Identify by letter the portion of the motor installation shown in Figure 8-1 that meets the purpose/requirement of the list provided.
picture overload is F disconnecting means is a control circuit protectionis C providing control circuit is e short circuit protection is b size of conductos is g controller is d
Motor branch circuit conductors must have an “ampacity” of not less than what percentage of the motor’s full-load current?
125 percent
The full-load current rating shown on the motor’s nameplate is not permitted to be used to determine the ampacity of the conductors.
True
The full-load current rating shown on the motor’s nameplate is permitted to be used to determine the overload protection for the motor.
True
According to the NEC, determine the minimum branch-circuit ampacity required for a 7 1/2 hp, 230-V, three-phase motor.
27.5 amps
A 20 hp motor and a 10 hp motor, both 460-V, three-phase, share the same feeder. Determine the minimum branch circuit ampacity required to size the feeder conductors.
47.75
For the motor branch circuit shown in Figure 8-2, state what undesirable operating condition each of the protective devices guards against.
a. short circuit and ground fault protection
b. overload protection
c. `control circuit over current protection
d. integral thermal protector
The starting current of a motor is approximately the same as its rated full-load current.
flase
With an inverse time circuit breaker, the higher the overcurrent, the longer the time required for the breaker to trip.
false
According to the NEC, what size of inverse time circuit breaker is permitted to be used for short-circuit and ground fault protection for a 5 hp, 230-V, three-phase squirrel-cage motor?
full load current FLC is 15.2
250 percent
38 amp inverse time circuit breaker
A motor overload condition is normally caused by
excessive motor load
Time-delay fuses provide both overload and short-circuit protection.
True
For any given horsepower motor, the nameplate full-load ampere rating is the same as that given in NEC tables. (True/Fa1se
False
In the majority of applications, motor overcurrent protection is provided by overcurrent _________________________ in the motor controller.
Relays
Motor control circuit conductors are not permitted to be tapped from the motor branch circuit conductors. (True/Fa1se)
False
Motor control circuits do not carry the main power current to the motor. (True/Fa1se) ____________
True
A motor ___________________________ 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 is an example of a motor controller?
a. Magnetic starter
b. Manual snap switch
c. Adjustable-speed drive
d. All of these
All of these
The purpose of a motor _______________________________ means is to open the supply conductors to the motor, allowing personnel to work safely on the installation.
disconnecting
The disconnecting means for the motor controller and the motor must open all ________________________ supply conductors simultaneously.
Ungrounded
In general, each motor requires a disconnecting means that is located within sight of the motor. “In sight of” is defined as being visible, and not more than ________________ feet in distance from one another.
50 feet
An isolation switch should not be operated under load. (True/Fa1se) ____________
TRUE
Motor control circuits can be the same voltage as the motor up to 600 V, or can be reduced by means of a control ______________________ .
transformer
Where one side of the motor control circuit is grounded, the design of the control circuit must prevent the motor from being started because of a __________________ fault in the control circuit wiring.
groiund
All motors tend to draw much more current during the starting period than when rotating at operating speed. (True/Fa1se) ____________
True
The current that flows before a motor begins to turn is called its
a. Locked-rotor current b. Full-load current c. No-load current d. Rated current
locked rotor
An across-the-line starter is designed to apply full line voltage to the motor upon starting. (True/Fa1se) ____________
True
Manual starters cannot be operated on/off by remotely located control devices. (True/Fa1se) ____________
True
The starter shown would be classified as which of the following types?
a. Single-pole manual b. Double-pole magnetic c. Three-pole magnetic d. Three-pole manual Answer
3 pole manuial
On a combination starter, the door cannot be opened while the disconnecting means is closed. (True/Fa1se) ____________
True
Complete a wiring diagram for the magnetic across-the-line starter shown in Figure 8-4, according to the two start/stop station line diagram shown in the text. Do not make any wire splices and run all wire connections from one terminal screw to the other.
pkay so the transformer primary is connect across tow of the lines of power.
X1 with the fuse goes through both stops in series
the 2 starts and the motor sealing contact go in parrallel
then the motor starter coil and the then the overload which will connect back up to the other side of the secondary of the transfomer with the ground
A reduced voltage starter:
a. Limits line voltage disturbances b. Reduces torque on starting c. Increases torque on starting d. Both a and b
D
Pressing the start button energizes coils ________________ and ____________ .
The motor is initially started through a _______________________ in each of the incoming lines.
After a preset time delay period, the ____________________ contact closes to energize coil _____________ , the contacts of which close to apply full voltage to the motor.
question 9 part 2
m and Tr
resistor bank
timer run contactor (it will byopass the resistor bank)
a. The instantaneous contacts of time coil TR are _____________ and _______________ .
b. The net result of initially pressing the start button is to energize coils _________________, ____________________, and ________________ .
c. After the timed contacts change state, coils _______________ and _____________ de-energize, and coil ______________ energizes, connecting the motor directly to the _____________ voltage.
TR1 amd TR2
TR, C2, and C3
c2 and c3
c1
full line voltage
Wye-delta starting involves connecting the motor windings in a __________________ configuration during the starting period and then in the ________________________ configuration after the motor has begun to accelerate.
wye
delta
Wye-delta starters can be used with motors where three or six leads of the stator winding are available. (True/Fa1se) ____________
False
Open transition wye-de1ta starters:
a. Apply voltage to the motor during transition b. Do not apply voltage to the motor during transition c. Do not create voltage surges during transition d. Both b and c
b
Part-winding reduced-voltage starters are used on three-phase motors wound for _________________________ -voltage operation.
dual
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. (True/Fa1se) ____________
flase
Which of the following starters increases the voltage gradually as the motor starts?
a. Autotransformer starter b. Solid-state starter c. Wye-delta starter d. All of these
Solid state starter
Soft-start motor starters limit motor starting current and torque by ramping the voltage applied to the motor during the starting. (True/Fa1se) ____________
True
Which of the following soft-start acceleration modes of operation regulates the maximum starting current to some preset value?
a. Dual ramp start b. Current limit start c. Linear speed acceleration d. Full-voltage start
b
a. This starter would be classified as a reduced-voltage type. (True/Fa1se) ____________
b. The use of the three power contacts connected in series is designed to reduce contact __________________ .
false`
arc
. This starter would be classified as an across-the-line type. (True/Fa1se) ____________
b. The voltage applied to the L1, L2, and L3 inputs is three-phase AC. (True/Fa1se) ____________
c. The function of the SCRs is to ____________________ the AC input voltage and provide a _______________________ DC voltage to the armature.
fasle
true
covert/variable
Interchanging any two line leads to a three-phase induction motor will reverse its direction of rotation. (True/Fa1se) ____________
true
A reversing starter requires ____________ set(s) of overload relays.
false
A reversing starter requires two contactors. (True/Fa1se) ____________
true
- In a three-phase reversing starter, the forward and reverse contactors are mechanically interlocked in order to:a. Allow the motor to accelerate to full speed
b. Prevent chattering of the starter coil
c. Prevent a short circuit from being created across the lines
d. Both band c
c
Pushbutton interlocking of reversing motor starters utilizes:
a. A mechanical link between the forward and reverse push buttons b. Momentary and maintained switch contacts c. Break-make switch contacts d. All of these
break and make
With pushbutton interlocking, the normally closed contact on the reverse push button acts like another __________________ push button in the forward circuit.
stop
a. Pressing the forward push button energizes coil _____________ .
b. Once operating in the forward direction, the motor is stopped by actuation of the ________________ push button or the __________________limit switch.
c. Both limit switches would be classified as being normally ________________ .
d. With both limit switches closed and the motor operating in the forward direction, pressing the reverse push button will change the direction of rotation. (True/Fa1se) ____________
F
blaj
The reversing starter for a single-phase capacitor start motor changes the direction of rotation by interchanging the _______________________________ winding leads, while those of the run winding remain the same.
start
As a result of the operation of the ___________________________________ switch, the single-phase capacitor-start motor must be allowed to slow down before you attempt to reverse the direction of rotation.
Centrifugal
he reversal of a DC motor is accomplished by
a. Reversing the two line leads to the motor
b. Reversing the direction of the armature current only
c. Reversing the direction of the field current only
d. Either b or c
d
The speeding up of a motor when unloaded is known as jogging. (True/Fa1se) ____________
false
When utilizing jogging control:
a. Care must be taken to prevent dynamic braking
b. The maintaining contact must not be connected
c. The thermal-overload element must be removed
d. All of these
B
a. This jog circuit would be classified as a control relay type. (True/Fa1se) ____________
b. When the switch is placed in the ____________________________ position, the maintaining circuit is not broken.
c. The dual-voltage primary of the control transformer is connected for the higher of the two input voltage ratings. (True/Fa1se) ____________
False
Run
False
The most common method of stopping a motor is to remove the _________________________________ voltage and allow the motor to coast to a stop.
applied
Which of the following braking systems applies to stopping a motor by reversing it while it is still running in the forward direction?
a. Dynamic braking
b. Regenerative braking
c. Plugging
d. Jogging
plugging
Which of the following braking systems can hold a motor stationary once it has stopped?
a. Dynamic braking
b. Eddy-current brake
c. Friction brake
d. Both a and b
Friction brake
A ____________________________________ starter is required when a motor is to be brought to a stop by means of plugging.
Derated
Plugging produces more heat in both the motor and starter than allowing a motor to coast to a stop. (True/Fa1se) ____________
True
A zero-speed or plugging switch prevents the motor from ________________________ after is has come to a stop.
Reversing
a. In this application the motor can be reversed but not plugged. (True/Fa1se) ____________
b. With the motor operating in the forward direction, the F zero-speed switch contacts will be _________________________ and the R zero-speed switch contacts will be _________________________ .
c. With the motor operating in the reverse direction, the F zero-speed switch contacts will be _________________________ and the R zero-speed switch contacts will be _________________________ .
True
Open/closed
Closed/open
- Dynamic braking is achieved by reconnecting a rotating motor to act as a __________________________________ immediately after it is turned off.
Generator
- DC injection braking is a method of braking in which:
a. DC is applied to the stator windings of an AC motor
b. AC is applied to the stator windings of an AC motor
c. DC is applied to the rotor windings of an AC motor
d. AC is applied to the rotor windings of an AC motor
Answer \_\_\_\_\_\_\_\_
sdsds
- Electromechanical friction brakes rely on fiction between a ___________________________ and ________________________ brake arrangement.
- Electromechanical friction braking is applied by energizing and de-energizing the brake _____________________________________ .
Drum and show
Operating cool
