WorksheetsS6-1: Mock CBT Week 12 (9/4/2018)
Total questions: 60
Worksheet time: 4hrs 14mins
What is the first action to be taken when a thermal overload trips an induction motor?
Short circuit the thermal trip
Disconnect the thermal trip
Replace the thermal trip
Reset the thermal trip
Which is an example of incorrect polarity in electrical installations?
Live and neutral conductors interchanged at a socket-outlet
Live conductor connected to the wrong phase conductor
Earth conductor not connected at a socket-outlet
Open-circuit neutral conductor
What is the most likely cause of a three-phase motor failing to develop enough torque to drive its load?
Reverse phasing
Drop in frequency.
Rise in frequency
Single phasing.
What is the operating resistance of a single-phase 230 V heating element rated at 3 kW?
7.7 Ω
13.1 Ω
17.6 Ω
25.5 Ω
What is the cause of an open circuit when testing the continuity of the line conductor in a lighting circuit?
Switch is open.
Neutral and line are interchanged.
Neutral is open circuit
Conductor insulation is failing.
What is the cause of a low resistance between line and earth on a single-phase motor?
Partial short-circuit winding to frame
Short-circuit line to neutral
Partial open-circuit
Short-circuited turns in a winding
Lack of lubrication causes hot a __________on a three-phase motor?
bearing
winding
shaft
wire
Which test connections are used when testing a single phase appliance for insulation?
L & N to E
E to N
N & E to L
L to N
What condition will cause a lamp controlled by a photoelectric cell to turn on?
movement within its range
increase the light level
change in temperature
decrease in light level
What component is required to control the starting capacitor in a single phase induction motor?
shunt coil
thermal trip
discharge resistor
centrifugal switch
Which protective measure provides protection against indirect contact? (unit 18)
obstacles
placing out of reach
insulation of live parts
automatic disconnection of supply
Which installation condition does not affect the current carrying capacity of a cable? (unit 18)
length of the cable
Type of material of the conductor
number of cables run together
air temperature around the cable
What type of material is Cu-OF?
Conventional copper
Conventional aluminum
High efficiency copper
High conductivity aluminum
Which relationship correctly identifies the requirements for overload protection?
Ib ≤In ≤Iz
Ib ≤Ir ≤Iz
Ib ≤Ix ≤Iz
Ib ≤Ih ≤Iz
What is used to divide electrical supply into subsidiary circuits, providing individual circuit protection?
Contactor.
PV inverter
Distribution Board.
Combined multi-port SPD.
Electric current passing through a human body or through an animal body when it touches one or more accessible parts of an installation or of equipment.
Reference: SBC 401 Definitions
touch current
touch voltage
step current
step voltage
Voltage appearing during an insulation fault, between simultaneously accessible parts.
Reference: SBC 401 Definitions
touch current
touch voltage
step current
step voltage
A nominal voltage not exceeding the relevant voltage limit (50 V a.c. or 75 V d.c.) between conductors or between conductor and earth.
medium voltage
high voltage
extra low current
extra low voltage
A nominal voltage exceeding 50 V a.c. or 75 V d.c., but not exceeding 1000 V a.c. or 1500 V d.c.
medium voltage
low voltage
extra low current
extra low voltage
What protective device provides the function of an residual current device with a circuit breaker, in the same enclosure?
RCD
RCBO
MCB
MCCB
What is the correct switching arrangements for an installation with an alternative supply available if the primary source fails?
the 2 switches should be interlocked so that only 1 switch can be on
the 2 switches should operate independently from each other
both supply switches must be able to open both supplies
both switches must only be operated manually
What is the main effect of annealing copper busbars?
Hint:
Annealing copper makes it softer and less brittle, which allows you to bend it without breaking it.
It improves malleability.
it corrodes more easily.
It improves conductivity
It is resistant to corrosion.
What is a requirement of a switch used for isolation?
The switch must be a semi-conductor device.
It must be designed to prevent unintentional closure.
It must always be positioned next to the equipment it isolates
When the switch is new the leakage current must not exceed 6 mA.
What is the minimum recognized shock current likely to cause muscular contraction?
Approximately 5 mA
Approximately 10 mA
Approximately 20 mA
Approximately 30 mA
What precaution must be taken to prevent the spread of fire when a wiring system passes between floors in multi-storey premises?
Trunking must be made of flame retardant material and provide IP2X protection
Trunking requires an internal fire barrier if the internal csa is less than 710 mm.
Hole around cables must be sealed to prevent any movement of the cables.
Sealing material must provide the same flame retardant properties as the building structure
Which measure provides protection against direct contact?
Electrical separation.
Barriers and enclosures.
Non-conducting location.
Automatic disconnection of supply.
What insulation resistance test voltage must be used when testing a 220 V circuit?
250 V
380 V
500 V
1000 V
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
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
Electrical resistivity has a unit of ____________________.
Ohms
Ohms * volts
Ohms/mm2
Ohms*mm
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.
Which method of installing a cable in a building void is permitted?
Hint: SBC Table 52-2
on insulators
in skirting trunking
without fixings
on a support wire
Which area is regarded as a medical location in the Saudi Building regulations?
Hint: SBC Chapter 710
Doctor's reception area
Hospital waiting room
Children's nursery
Treatment room
What is the requirement for a motor installed in an area where there are stored materials which pose a risk?
Hint:
SBC 42-2.3
SBC Table 51-1
Motors must be placed outside this area
motor must be rated no more than 0.375 kW
motor must be rated no more than 5 kW
motor must be protected against excessive temperature rise
What is classified as a hazardous location in Saudi Building regulations?
Hint:
SBC definitions
SBC Table 721-1
an area where there is inert gas present
an area where there are explosive gas present
an area containing rotating machinery
an area containing switchgear
Which requirement applies to a construction site where there is more than one source of supply?
Hint:
SBC 704:31-3.1.13
equipment must be identified for use of one particular supply
each supply must be protected by 200 mA RCD
equipment supply voltage rating must exceed 110 V
each supply must form part of a TN-S system
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
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
What is the minimum IP rating of electrical equipment installed in locations where hose water is used regularly (yards, car-washing bays)?
Hint: SBC Table 51-1
IPX2
IPX3
IPX4
IPX5
