What is the maximum number of trip coils required for a three phase motor?
2
3
5
Not required
What type of three phase motor has the ability to correct its own power factor and the power factor of other devices connected to the same line?
Resistance-start induction-run
Squirrel-cage induction
Synchronous
Wound-rotor induction
What is the maximum time-delay fuse that can be used with a three-phase motor of the full load current?
125%
175%
225%
300%
How can locked rotor current be described?
It is the current that wound rotor motor reaches at synchronous speed
It’s the full load current of a squirrel cage motor
It’s the stall current of a three-phase motor
It’s the starting current of a squirrel cage motor
The over current device will not permit a motor to start. What is the maximum time-delay fuse that can be used with a three-phase motor of the full load current?
400%
What is the basic principle of operation for all three-phase motors?
A rotating magnetic field
DC field operation
Brushless field excitation
Maintenance
A wound rotor motor has a strong starting torque and maintains a smooth acceleration from start to full speed. What percent of full load torque is usually produced?
50-100 percent
100-200 percent
200-300 percent
300-400 percent
What is the phase voltage of a three-phase 600 volt squirrel cage connected delta?
208V
347V
600V
750 V
What does the service factor reveal about the motor?
The length of time the motor may be operated before resting
The expected life of a motor
How often the motor should be serviced
How much of the motor can be continuously loaded without damaging it
What is the conduction called if one phase of a three-phase motor opens?
Double phasing
Single phasing
Triple phasing
Free running
When installing an electrical motor that is totally enclosed, non-vented, with class F insulation rating, the conductors supplying it needs to be rated for what temperature?
75C
90C
110C
125C
A nine lead motor may be connected in wye or delta internally. If this connection is been tested by checking T7, T8, T9 what is it been tested for?
Lugs
Polarity
Continuity
Rotation
What is the temperature rating of the conductors supplying a motor with a class H insulation rating?
100C
120C
What is the maximum feeder conductor ampacity required to supply a bank of three phase motor are: 96 A, 27A, and 156A
279A
318A
337A
303A
What size of R90 copper conductor is used in a feeder conduit to supply three motors having a full load current of 100amps, 20 amps, and 10 amps? 75 degree rated
#1/0 AWG
#1 AWG
#400mcm
#2/0 AWG
What is the speed at 60 Hz of a 12 pole synchronous motor?
120 rpm
300rpm
600 rpm
1200rpm
In a wound rotor motor, the torque characteristic can be altered by?
Adding or removing external resistance
Adding and removing external inductance
Adding or removing external capacitance
Torque may not be altered
Three-phase motor windings are installed ____ electrical degrees apart from each other
90
120
180
270
What is the term used to describe the amount of torque required to pull the rotor into synchronous speed?
Cut-out torque
Cut-in torque
Pull-out torque
Pull-in torque
What is the term used to describe the angle between the centre of the stator pole and the centre is the rotor pole?
Torque angle
Angle of incidence
Phasing angle
Synchronous angle
What is the advantage of a synchronous motor?
Constant speed from no load to full load
Lower voltage starting
Can run on either AC and DC
Speed can be controlled
What size time-delay fuse is required for a three phase, 25hp, 600v, scim
20 A
30A
15A
40A
What meter is used to check phasing in a 3-phase motor when it is de-energized and out of service?
Clamp-on meter
Multimeter
Phase rotation meter
Phase sequence meter
What powers the field generation in a typical synchronous motor?
External resistor
External DC source
External AC source
External capacitors
The basic principle of all 3 phase motors for synchronous motor is?
Reluctance
Capacitance
Induction
By checking leads T7, T8, T9 of a nine lead motor, an electrician can determine
The voltage of the motor
The FLA of the motor
The winding connection (wye or delta)
The service factor of the motor
What are synchronous motor mainly used for
Fan
Pumps
Compressors
All of the above
The insulation class rating of a totally enclosed non-ventilated motor operating at 90 degrees is
Type A
Type F
Type B
Type H
In dual voltage 3 phase motors, the leads are connected in ____ for low voltage and in ____ for high voltage
Parallel-series
Series-parallel
Delta-wye
Wye-delta
To find the size of fuse holders that accommodates fuses supplying a group of motors, you must take ____ off the largest motor current and add to this valve of the full load currents of all other motors in a group that may be in operation at the same time.
115%
150%
200%
Which markings are used to designate the rotor terminals of a wound rotor motor?
L1 L2 L3
F1 F2 F3
M1 M2 M3
T1 T2 T3
In order to not trip, what is the maximum percent rating for an instaneous trip circuit breaker of an AC motor?
700%
900%
1300%
1500%
What is the speed of rotation of the magnetic field called in a three-phased motor?
Magnetic
Slip
Rotor
What is the proper rating of a time-delay fuse for a 230v, 22.38 KW, auto-transformer start continuous duty motor
100Amp
125Amp
150Amp
225Amp
A three-phase motor has a synchronous speed of 1800RPM, operates at a frequency of 60Hz and has a slip speed of 100RPM. What is the rotor speed of the motor?
1700 RPM
1900 RPM
2000 RPM
2100 RPM
What is the purpose of the centrifugal switch in split phase motor?
It removes the start winding from the motor in split phase motors
It adds the start winding from the motor circuit
It removes the run winding from the motor circuit
It adds the run winding from the motor circuit
What is the speed at which the centrifugal switch of a split phase motor will operate?
60%
65%
70%
75%
How is the rotor of a 15 hp synchronous motor operating on line voltage excited?
AC voltage
Induced magnetic field
AC line voltage
DC current
Which starting method provides the highest torque per ampere?
Auto-transformer
Across the line
Primary resistor
What part of the wound rotor motor differs from that of a squirrel cage induction motor?
Stator
End bells
Bearings
What size time delay fuse can be used on a 3 phase, 230V, auto transformer starting motor consuming 22.38 KW of power
70 amps
80amps
90 amps
100amps
What does increasing the frequency of the supply voltage to an induction motor cause?
Increased speed
Decreases speed
Increased torque
Decreased torque
A nine-lead dual voltage three-phase SCIM is connected in the lower voltage delta arrangement. Which terminals are connected to each other?
L1-T1, T7-T4, L2-T2, T8-T5, L3-T3, T9-T6
L1-T1-T7-T6, L2-T2-T8-T4, L3-T3-T9-T5
L1-T1-T8, L2-T2-T7, L3-T3-T9, T4-T5-T6
L1-T1,L2-T2,L3-T3,T7-T4,T8-T5,T9-T6
What is the ampacity of conductors feeding a 3 phase, 230V, SCIM, continuous duty motor rated at 20hp, 10hp, 1Hp, and 5Hp?
77.1A
88.3A
114.9A
116.6A
What meter is used to check the input phasing before installing a three-phase motor?
Wattmeter
Motor rotation meter
Syncroscope
What effect does increasing the frequency of the supply have on the speed of the rotating magnetic field?
Increases
Decreases
No change
Changes direction
How does the starting current of a split phase motor compare to its full load current?
It’s much higher than the FLA
It’s much lower than the FLA
It’s equal to the FLA
It’s equal to the stall current
What information is required to size the overload protection of a 15Hp l, 600V, three-phase motor?
HP & FLA
SF AND FLA
V and FLA
Wire size and SF
A 5 Hp, 3 phase motor has a voltage of 208v and draw a 12A. It has a power factor of 95%. What is the efficiency?
75.6%
90.8%
110%
157%
Which variables are identified by the motor service factor when considering the maximum continuous permissible load?
Voltage and amps
Voltage and frequency
Amps and frequency
RPM and voltage
A synchronous motor has a lagging power factor. How is the corrected?
Over excite the field
Add a capacitor
Increase the load reduce the load
Reduce the load
Which 3 phase motor provides maximum starting torque?
Capacitor run
Capacitor start
Induction run
Resistance run
