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WorksheetsCBT Practice 15/4/2018
Total questions: 60
Worksheet time: 9hrs 20mins
All are methods of starting three-phase synchronous motor except:?
By using a damper winding.
By using a slip-ring induction motor.
By using a star delta motor starter.
By using a small D.C machine.
When comparing the capacitor start, capacitor run induction motor with other types of single phase induction motor, it has ______________ starting torque and ___________ power factor and efficiency.
higher ; worse
lower ; better
lower ; worse
higher ; better
When comparing the capacitor run induction motor with the capacitor start one, the capacitor run motor has _____________ starting torque and ___________ power factor and efficiency.
higher ; worse
lower ; better
lower ; worse
higher ; better
When comparing the capacitor start induction motor with the spilt phase one, the capacitor start motor has ___________ starting torque and _________ inrush current.
higher ; higher
lower ; lower
lower ; higher
higher ; lower
Split phase motors have _________ starting torque and ________ power factor.
high ; poor
high ; high
poor ; poor
poor ; high
When there are minimum two alternating fluxes, having a phase difference between them, then the resultant magnetic field is.:
static
rotating
alternating
pulsating
In single phase induction motors, the starting winding is made ______________ whereas the running winding is made with ______________.
highly capacitive ; highly inductive
highly inductive ; highly resistive
highly resistive ; highly capacitive
highly resistive ; highly inductive
Single phase induction motors are extensively used in:
Large machines of high speed.
Heavy-duty machines.
Low power applications such as domestic and light-industrial appliances.
Heavy industrial machines
The wattage for the single-phase induction motor is in the range of:
Multiple kilowatts.
Fractional kilowatt.
Tens kilowatts.
Hundreds kilowatts
The type of motor that is used in applications such as ceiling fans, food mixers, refrigerators, vacuum cleaners, portable drills, hair driers is:
Single-phase induction motor.
Three-phase squirrel-cage induction motor.
Three-phase wound-rotor induction motor.
Three-phase synchronous motor
As compared to the squirrel-cage motor, the wound-rotor (slip-ring) induction motor has __________ inrush current and _____________ starting torque.
higher ; lower
lower ; lower
higher ; higher
lower ; higher
What type of magnetic field is produced in the rotor winding of a three-phase synchronous motor when it is energized?
oscillating
constant
rotating
pulsating
What conditions must be satisfied before connecting two transformers in parallel to share a common load?
Same inductance, same kVA rating
Same number of polarity turns, same voltage regulation
Same polarity resistance, same current ratio
Same voltage ratio, same percentage impedance
What conditions must be satisfied before connecting two transformers in parallel to share a common load?
Same inductance, same kVA rating
Same polarity, same phase sequence
Same polarity resistance, same current ratio
Same number of polarity turns, same voltage regulation
All the followings are advantages of operating transformers in parallel except for:
To maximize the voltage rating of the supply.
To maximize electrical power system efficiency.
To maximize electrical power system availability.
To maximize power system reliability.
A transformer delivers 150 volts at no-load and the voltage drops to 141 volts at full load, the regulation would be:
Hint:
VR = { (VNL - VFL) / VNL } x 100%
4%
5%
6%
7%
If E represents the no-load secondary voltage and represents the full-load secondary voltage, the percentage regulation of a transformer is given as:
VR = [ (E - V) / E ] x 100%
VR = [ (E - V) / v ] x 100%
VR = [ (E / E - V) ] x 100%
VR = [ (V / E - V) ] x 100%
Which property of a transformer is measured by the change in output voltage from no-load to full-load conditions?
voltage ratio
transformer efficiency
voltage regulation
power transformer
With the decrease in temperature, the viscosity of the transformer oil will:
Decrease little
increase
decrease much
does not get affected
Pour point of transformer oil is:
The minimum temperature at which oil just start to vaporize under standard test condition.
The minimum temperature at which oil just start to boil under standard test condition.
The minimum temperature at which oil just start to flow under standard test condition.
The minimum temperature at which oil just start to become intolerably hot under standard test condition.
If the resistance of supply line is 0.32ohms, and the resistance of protective earth conductor is also 0.32 ohms. Find the total earth fault loop impedance of the system (Zs), if the external impedance (Ze) is given as 0.15ohms.
0.79 ohms
0.47 ohms
0.32 ohms
0.64 ohms
Based on Table 41.3 of the SBC 401 given below, what is the maximum earth fault loop impedance in a system connected in a MCB, 16A, type B?
2.30 ohms
4.60 ohms
2.87 ohms
1.44 ohms
_______________ is the low impedance path to earth of fault current.
Fault current loop
Earth Fault loop impedance
Earthing Loop
Leakage current loop to earth
If the voltage drop across the conductor is 6.7%. Which of the following is true?
The conductor is good to be used
The conductor is not long enough
The conductor size (CSA) must be increased
The conductor size (CSA) must be decreased
In the Earthing System, PEN stands for ________________,
Planet Earth Nations
Proposed earth and neutral
Protective earth neutral
Protect the Earth’s Nature
If the size of the conductor is increased, the voltage drop of the conductor will
increase
decrease
be the same
not be known
Which of the following conductors will have the highest voltage drop?
25 meter 2.5 mm2 black conductor
10 meter 2.5 mm2 brown conductor
30 meter 2.5 mm2 gray conductor
20 meter 2.5 mm2 blue conductor
If Ib<= In <= Iz
which of the following conditions is correct?
IN>IB
IZ<IB
IN<IB
IN>IZ
What is the minimum CSA of conductors that can be used for socket-outlet installations?
1.5 mm^2
2.5 mm^2
4.0 mm^2
6.0 mm^2
Which type of circuit breaker is suitable for purely resistive loads or loads with very small inductive component?
Hint: The minimum trip current is 3 to 5 times the rated current.
Type A
Type B
Type C
Type D
One of the bellow is an example of Earthing types :
TMT
MTANT
TN-C-S
S-C-TN
According to SBC401 the allowance for a voltage drop in consumer’s installations is:
40%
4% or more
4% or less
5%
Electrical resistivity has a unit of ____________________.
Ohms
Ohms * volts
Ohms/mm2
Ohms*mm
If a socket outlet circuit is to be installed in a washing area, what type of protective device would you choose?
MCB
RCBO
MCB or RCBO
CNT
According to SBC401, if the live cable CSA for a given circuit is 50 mm2, the earthing wire CSA should be________________.
2.5mm2
16mm2
50mm2
25mm2
In the coordination of conductor and overcurrent protection device, which of the following is true?
Ib ≤ In ≤ Iz
In ≤ Iz ≤ In
I2 ≤ Ib ≤ Iz
Iz ≤ Ib ≥ In
According to SBC 401, the PEN conductor shall have the color of _____________.
Blue
Green and Yellow
Black
Brown
According to SBC 401, the conductor for Phase 2 of three-phase a.c. circuit shall have the color of _____________.
Blue
Red
Black
Brown
Inside the bathroom, which area or object is Zone 0?
The door
The bathtub
The mirror
The ceiling
What degree of protection is necessary for the installation of electrical equipment in Zone 0 of a swimming pool?
IPX2
IPX4
IPX6
IPX8
What is the maximum residual operating current of an RCD protecting socket-outlets installed in Zone 3 of bathtub and shower basins?
300 mA
30 mA
30 A
300 A
What is the maximum operating temperature of a PVC insulation according to SBC401?
60°C
70°C
80°C
90°C
What does RCD mean
Resistive and Capacitive Device
Residual Capacitance Device
Resistive Current Device
Residual Current Device
The earthing system applicable for Caravans electrical installation is ______________
TT
TN-C
IT
TN-S
What is minimum size of PE conductor to be used in caravan electrical installation?
1.5 mm square
4.0 mm square
1.0 mm square
10 mm square
Which protective measure provides protection against indirect contact?
obstacles
placing out of reach
insulation of live parts
automatic disconnection of supplu
What temperature factor must be applied when confirming compliance of measured fault loop impedance?
0.5
0.66
0.75
0.8
What type of socket outlet circuit does not require additional protection provided by a 30 mA RCD?
Socket-outlet circuits used by ordinary persons
Socket-outlet circuits located within wet areas
Socket-outlet circuits used by skilled persons
Socket-outlet circuits located outdoors
What is the minimum cross-sectional area of a line and CPC, in order to provide ADS in the circuit with a maximum permitted Zs of 0.36 Ω if Ze is 0.17 Ω using the information in the figure below. (t = 0.4s, k = 115)
1.5/1.5 mm2
2.5/2.5 mm2
4.0/4.0 mm2
6.0/6.0 mm2
What test instrument is used to confirm the continuity of protective conductors?
voltage indicator
low resistance ohmmeter
insulation resistance tester
earth electrode resistance tester
Checking that the measured test results meet the required values will enable the inspector to confirm that the electrical installation is:
correctly installed
safe to be in service
nice to see
expensive
Which of the following correctly describes the relationship between prospective fault current and the fault current rating of a circuit breaker?
Ipf >= Icn
Ipf <= Icn
Ipf >= In
Ipf <= In
Which of the following instruments must be used to measure the earth electrode resistance for a standby generator?
earth fault loop tester
IR tester
low resistance ohmmeter
earth electrode resistance tester
Which test is used to confirm the correct connection of a 3 phase socket outlet.
phase sequence
IR test
earth fault loop
operation of residual current devices
Which test would be used to confirm that exposed conductive parts are connected to the main earthing terminal.
IR test
prospective fault current
earth fault loop
continuity of protective conductors
In order to undertake the inspection and testing of an electrical installation a person must be a____________.
competent person
principled person
duty person
registered person
Which installation condition does not affect the current carrying capacity of a cable?
Length of the cable.
Conductor material.
Number of cables run together.
Air temperature around the cable
Which document must be attached to a Test Report?
Instrument calibration certificate.
Saudi Building Code (401).
Generic risk assessment.
Inspection Schedule.
Which document must be attached to a Test Report?
Instrument calibration certificate.
Saudi Building Code (401).
Generic risk assessment.
Inspection Schedule.
What is the effect on an installation if the supply voltage drops below the lower voltage limit?
Circuit breakers may fail to operate if a short-circuit occurs.
Contactors may de-energize, switching off motors.
Discharge lighting may produce more light.
Heaters may overheat and cause a fire.
