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WorksheetsDIPLOMA CBT PRACTICE QUESTIONS
Total questions: 204
Worksheet time: 16hrs 11mins
Where is Zone 1 located within a bathroom?
Directly above Zone 2, with a maximum height of 3.5 m
Below the bath if access is with a tool
Directly above the bath to a height of 2.25 m
At least 0.6 m from the side of Zone 0
What is a typical application of split phase induction motors?
Domestic appliances
Large constant speed machines
Driving heavy loads requiring high starting torque
Driving industrial loads for long periods of time
What is the basic principle of sound transmission?
Electrochemical impulses
Wave propagation
Mechanical pressure
Molecular refraction
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
Which type of telecommunication cable is most effective at reducing noise pickup?
Untwisted pair
Un-shielded twisted pair
Shielded twisted pair
Twisted pair
What is the formula for power transfer from the primary winding to the secondary winding referring to the phasor diagram below?
A. P = Vp Ip cosΦp
A. P = Vp Ip cosΦ1
A. P = Vp Ip sinΦp
A. P = Vp Ip sinΦp
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
Which procedure should be carried out immediately after testing to confirm electrical isolation and before starting work?
Fit a sign to a remote isolator
Test for continuity
Lock off at a remote isolator
Retest the voltage indicator
What type of magnetic field is produced in the stator winding of a three-phase induction motor when it is energized?
Oscillating
Static
Rotating
Pulsating
What requirement applies on a construction site when Automatic Disconnection of Supply (ADS) is the protective measure?
Reduced low voltage systems must not be used
Socket-outlets must be protected by a 100 mA RCD
Minimum csa of the cpc must be not less than 4 mm2
Conventional voltage limit (UL) must not exceed 25 V ac
What type of motor is used when operating in a corrosive atmosphere?
Drip-proof
Semi-enclosed
Fan-cooled
Pipe-ventilated
What is the maximum residual operating current of an RCD that provides protection against contact with live parts?
10 mA
30 mA
100 mA
300 mA
What is a suitable method for planning maintenance of a large number of tasks?
Work study chart
Mesh analysis
Critical path analysis
Risk assessment
What is the function of preventative maintenance?
To ensure plant is safe and reliable
To repair faulty machinery
To commission new plant
To remove faulty equipment from service
What are the required operating characteristics of transformers used in welding machines?
Low secondary current, low secondary voltage
High secondary current, low secondary voltage
High secondary current, high secondary voltage
Low secondary current, high secondary voltage
What is the cause of a hot bearing on a three-phase motor?
Lack of lubrication
Overheated windings
Poor ventilation
Single phasing
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 prime mover is used with a low-speed portable three-phase alternator?
Reciprocating engine
Water turbine
Steam turbine
Diesel engine
What is the main effect of annealing copper busbars?
It improves malleability
It corrodes more easily
It improves conductivity
It is resistant to corrosion
What color is used to identify Line 2 of a three-phase power circuit?
Blue
Black
Brown
Gray
How can a three-phase synchronous motor be started?
By using a pony motor
By using a squirrel-cage rotor
By using a star delta motor starter
By using a rotor resistance starter
Which measure provides protection against direct contact?
Electrical separation
Barriers and enclosures
Non-conducting location
Automatic disconnection of supply
Which method may be used to safeguard an installation against overvoltage?
Fit a surge protective device at the main terminals
Connect the installation to an overhead distribution system
All appliances have an impulse withstand voltage of 6 kA
Installation has a main fuse or circuit breaker which disconnects the maximum fault current
What is the minimum short circuit rating of the user's equipment at the point of connection to a 380 V three-phase supply?
20 kA
21 kA
25 kA
30 kA
What is the secondary current for a single-phase transformer which has a primary current of 50 A and a turns ratio of 2:1?
25 A
50 A
100 A
200 A
What is the essential property of the oil used in transformer tanks to facilitate cooling?
High viscosity
Low hydrogen content
High carbon content
Low viscosity
What is the maximum permitted voltage to earth for a reduced low voltage single-phase system used on a construction site?
220 V
110 V
55 V
25 V
Which parts of an electrical installation are connected by the earthing conductor?
Exposed conductive parts and main earthing terminal
Main earthing terminal and earth electrode
Two extraneous conductive parts
Two exposed conductive parts
What factor affects the value of earth fault loop impedance of a circuit?
Resistance of the neutral conductor
Type of cable insulation
Rating of the circuit protective device
Length of circuit cable
What is indicated by a low insulation resistance reading between L1 and L3 lines on the delta connected stator of a three-phase induction motor?
Faulty insulation on L3
Faulty insulation on L1
Faulty insulation on L1 and L3
Faulty insulation on L1, L2 and L3
What is a requirement for the location for an overhead distribution circuit on a caravan site?
he overhead cable must be positioned at least 2 m outside of any caravan pitch
he cable can be run anywhere providing it is above 3.5 m from the ground
The cable can only be used in areas where there are no vehicle movements
The overhead cable supports must be clearly visible if vehicles are present
What insulation resistance test voltage must be used when testing a 220 V circuit?
250 V
380 V
500 V
1000 V
What is a hazard when terminating copper telecommunication cables?
Excessive noise
Laser light
Flying offcuts
Sharp edges
What is the effect on an installation forming part of an MEN system if the PEN conductor develops high impedance?
Voltage will appear on earthed metalwork
Installation neutral conductor will overheat
Protective devices will operate more quickly under fault conditions
Voltage will only appear on earthed metalwork if an earth fault occurs
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 transfer
What type of rotor is used in a slip-ring induction motor?
Solid rotor
Wound rotor
Squirrel cage rotor
Double cage rotor
What is an advantage of an underground wiring system when compared with an overhead wiring system?
It is easily accessible
It is cheaper to install
It will use a smaller csa conductor
It is protected from damage by winds
What is the purpose of the Buchholz relay used with large distribution transformers?
To record operating times
To check voltage levels
To monitor gas levels
To check current flow
What is the purpose of equipotential bonding?
To earth an exposed conductive part
To earth the metal casing of Class I equipment
To provide a conducting path in the event of an earth fault
To keep two exposed conductive parts at or about the same potential.
Which type of communication connection is used between extensions of a private telephone system?
Distribution frame
Rotary
Tie-line
Power fail
What is the purpose of plant history cards?
To record maintenance operations
To enable fault-finding
To extend manufacturers' warranty
To review capital costs
Which area is considered to be a hazardous location in the Saudi Building Regulations?
Area containing a bath or shower
Area containing a high concentration of water vapor
Area including a restrictive conducting location
Area with a concentration of flammable vapors
How can the direction of rotation of a series universal motor be reversed?
Change the polarity of the supply
Reverse the armature or field winding connections
Reverse the armature and field winding connections
Change the frequency of the supply
Which type of drawing is used to directly inform the connection of telecommunication cables?
Schematic
Block
Ladder
Wiring
What is the condition for maximum starting torque in an induction motor?
Rotor reactance is twice the rotor resistance
Rotor reactance is half the rotor resistance
Rotor reactance is a quarter of the rotor resistance
Rotor resistance is the same as rotor reactance
What is the minimum recognized shock current likely to cause muscular contraction?
Approximately 5 mA
Approximately 10 mA
Approximately 20 mA
Approximately 30 mA
Why are power transformers operated in parallel?
To increase the current rating of the supply
To maximize power supply flexibility
To improve voltage regulation
To reduce heat loss
What type of single-phase motor is shown in the diagram below?
Capacitor start
Capacitor run
Capacitor start, capacitor run
Permanent split capacitor
What action must be taken when carrying out a visual inspection of a new electrical installation?
Installation must be totally isolated from the supply
All testing must be carried out before the inspection starts
Only the wiring and control equipment is inspected
All cables are inspected throughout their length
Which type of PLC output is used for the high-frequency switching of ac loads?
Relay
BJT
Triac
MOSFET
What is the minimum cross sectional area (csa) of a circuit protective conductor (cpc) when selected from the table below, if the live conductors are 25 mm2?
8 mm2
16 mm2
32 mm2
25 mm2
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 mm2
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
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
What is the danger of opening the secondary circuit of an energized current transformer?
High voltage appears across the secondary
Large current flows in the primary
High voltage appears across the primary
Large current flows in the secondary
What is the operating resistance of a single-phase 230 V heating element rated at 3 kW?
690 Ohm
176 Ohm
76.7 Ohm
17.6 Ohm
What is established by analyzing maintenance records?
Machine maintenance
Replacement dates for equipment
Initial purchase prices
Frequency of maintenance tasks
What method is used to secure control panel wiring?
Insulation taping
Strapped harness
Cleating
Clipping
What is the maximum residual operating current of an RCD for supplementary protection?
15 mA
30 mA
150 mA
300 mA
Which method of installing a cable in a building void is permitted?
On insulators
In skirting trunking
Without fixings
On a support wire
Which area is regarded as a medical location in the Saudi Building regulations?
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?
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?
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?
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
What is the minimum IP rating of electrical equipment installed in Zone 2 of an indoor swimming pool?
IP X2
IP X4
IP X5
IP X8
Where can underground cables without additional protection be used in a caravan park?
Anywhere in the park, if buried at least 300 mm deep
Only in areas where there is caravan traffic
Only within caravan pitch area
Outside the area of a caravan pitch
Which installation method is suitable for an underground system?
thermosetting insulated and sheathed cable laid directly in the ground
thermosetting insulated steel wired armored cable laid directly in the ground
thermoplastic insulated cable installed directly in a concrete duct
thermosetting insulated and sheathed flexible cable in a steel conduit
What is the shape of the laminations used in the magnetic circuit of a single phase shell-type transformer?
L-L
T-T
L-E
E-I
What is the recommended minimum distance between a 66 KV transformer and other oil-filled equipment?
2 meters
4 meters
6 meters
10 meters
What quantities are represented by the letters A, B and C on the No load transformer phasor diagram?
A=Primary voltage, B=no load current and C=Flux
A= no load current, B= Primary voltage and C=Flux
A= Flux, B= Primary voltage and C= no load current
A= Primary voltage, B= Flux and C= no load current
What two power losses occur in a transformer when operating on no-load?
Mechanical losses, core losses
Frictional losses, heat losses
Rotational losses, copper losses
Copper losses, core losses
What is the relationship between the VA rating of a transformer and the internal percentage impedance Z?
VA ∝ 1/ Z
VA ∝ Z
VA ∝ 2Z
VA ∝ Z/2
What two 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.
What type of transformer is used for interconnecting high voltage transmission systems operating at different voltage levels?
Current transformer
Double wound transformer
Voltage Transformer
Autotransformer
What is the danger of disconnecting a direct current from a power transformer winding under a test?
Large current circulates
Heat is generated
High voltage is generated
Power surge occurs
What is the effect of changing over two of three line conductors supplying a three phase induction motor?
No effect on the motor
The direction of rotation is reversed
It causes a short circuit
The motor will not run
When is the stator winding of a three phase squirrel-cage induction motor connected in star?
When in full load
When running at rated speed
When on light load
When starting the motor
What is the percentage slip of a motor at full load speed where the nameplate details are:
f= 50Hz
Poles=4
full-load speed=1440 rpm
0.01 ( or 1%)
0.02 (or 2%)
0.04 (or 4%)
0.08 (or 8%)
What is the ideal electrical angle of separation of the start and run windings to create a rotating magnetic field in a split phase induction motor?
30 Degree
60 Degree
90 Degree
120 Degree
How can the direction of a capacitor start single phase motor be reversed?
Reverse the connection to the capacitor
Reverse the connection to the start winding
Reverse the polarity of the supply
Reverse the connection of the start and run windings
When are single phase series universal motors used?
When high starting torque is required
When starting on no load is required
When constant speeds are required
When low speed drives are required
What is the main advantage of an HRC fuse used to protect electrical motors?
It discriminates between short and long time overload
It carries up to 100% overload for up to 2 hours
It opens immediately if the rating is exceeded by 20%
It opens the circuit on overload and restores the supply when the fault clears
At what speed three-phase cylindrical two-pole synchronous alternator rotates when connected to a 50 Hz infinite busbar system?
1000 rpm
1500 rpm
3000 rpm
6000 rpm
What is a common use of a portable alternator?
To boost the grid during heavy demand
As a standby supply if the main supply fails
Where a low-voltage dc supply is required
Where a variable frequency supply is required
Which fixing method is used to install industrial equipment on a DIN rail in a control panel?
Adhesion
Clipping
Cleating
Riveting
What is the effect on an electronic signal conditioning circuit when radiated interference is present?
Distorted signal processing
Attenuation of signal noise
Overheating of components
Reduction of supply voltage
What type of maintenance is carried out on a machine which is functioning correctly after it has run for a number of hours?
Time based preventive maintenance
Condition based preventive maintenance
Time based corrective maintenance
Condition based corrective maintenance
What factor from a vibration analysis identifies the severity of vibrations in a rotating machine?
Velocity
Frequency
Amplitude
Acceleration
Why is it necessary to give priority to tasks on the critical path of a maintenance plan?
To ensure the task is completed on time
Because they are the only tasks which need to be completed
Because they are the most expensive to complete
To maximize the time required by skilled workers
What data should be recorded in the equipment management module of a computer managed maintenance system (CMMS)?
Quality reports
Manufaturers’ details
History of machine performance
Maintenance and refurbishment procedures
What is function of the capacitor across the supply terminals of a discharge lamp?
To prevent radio frequency interference
To assist starting the lamp
To maintain lamp operation
To provide power factor operation
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
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
Which test instrument is used to confirm the continuity of protective conductors?
Voltage indicator
Low resistance ohmmeter
Insulation resistance tester
Earth electrode resistance tester
Which component is essential in a MEN system to provide a return path for installation earth fault currents?
Earth electrode
Neutral-earth link
Supply protective device
Main protective bonding conductor
What type of earthing system would include an earth electrode as part of the consumer’s installation?
TN-C-S.
TN-S.
TN-C
TT
What is the minimum csa of a copper protective conductor which is separated from the supply cable and mechanically protected?
1.5 mm2
2.5 mm2
4.0 mm2
6.0 mm2
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 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
Which formula is used to determine the maximum permitted earth fault loop impedance Zs?
Ze
Ze + R1
Ze + R2
Ze + R1 + R2
Which relationship correctly identifies the requirements for overload protection?
Ib ≤ In ≤ Iz
In ≤ Ib ≤ Iz
Iz ≤ In ≤ Ib
Ib > In > Iz
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 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
Which document must be attached to a Test Report?
Instrument calibration certificate.
Saudi Building Code (401).
Generic risk assessment.
Inspection Schedule.
What temperature factor must be applied when confirming compliance of measured fault loop impedance?
0.5
0.66
0.75
0.8
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 protective measure provides protection against indirect contact?
obstacles
placing out of reach
insulation of live parts
automatic disconnection of supply
What is the fundamental safety principle of protection against direct contact?
To prevent an earth fault from occurring
To prevent insulation from becoming damaged
To prevent current from passing through body
To prevent exposed metal work from becoming live
Decide which statement underneath best describes the direct contact from an electrical point of view:
A direct contact refers to the contact between two live lines
A direct contact refers to the contact between one live line to the earth
A direct contact refers to a person coming into contact with a conductor which is live in normal circumstances
A direct contact refers to a person coming into contact with an exposed conductive part which is not normally alive, but has become alive accidentally (due to insulation failure or some other cause).
What is the correct switching arrangement 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 used to divide electrical supply into subsidiary circuits, providing individual circuit protection?
Contactor.
PV inverter
Distribution Board.
Combined multi-port SPD.
What type of material is Cu-OF?
Conventional copper
Conventional aluminum
High efficiency copper
High conductivity aluminum
What prevents sound travelling in a vacuum?
Sufficient energy levels are not present
A medium is not available for molecular vibration
Insulating materials absorb the vibrated molecules
Insufficient energy is generated for propagation
What is (ISDN)?
A propagation method
A facsimile system
A transmission signal
A communication standard
What method is used to identify individual telecommunications cables?
Screening
Segregation
Labeling
Taping
Which telecommunication cable has infinite bandwidth?
Un-shielded twist pair
Fiber Optic cable
Co-axial Cable
Shielded twist pair
When must category 6 network cable be used instead of category 5?
When bandwidth need to be >100 MHz
When a data transmission speed is < 1 gigabit
When the bandwidth needs to be <100 MHz.
When a data transmission speed is < 1 megabit.
What is classified as a hazardous area in the Saudi building requirements?
An area where there is inert gas present
An area where there is explosive gas present
An area containing rotating machinery
An area containing switchgear
What is the requirement for a motor installed in an area where there is a fire risk?
Motor must be placed outside this area
Motor must be rated no more than 0.375 kW
Motor must be sited at least 0.5 m from stored materials
Motor must be protected against excessive temperature rise
What are the conditions required for SELV and LV circuit be installed in the same conduit?
All cables must be insulated to the highest voltage present.
All cables must have the same insulation material.
All cables must be insulated to the lowest voltage present.
All cables must be part of the same ac circuit.
What color is used to identify Line 2 of a three-phase power circuit?
Blue
Black
Brown
Gray
What is the recommended minimum distance between a 60 KV transformer and equipment?
2 meters
4 meters
6 meters
10 meters
What is the percentage slip of a motor at full load speed where the nameplate details are: f= 50Hz, Poles=4, full-load speed=1440 rpm
4%
5%
6%
7%
1. Which formula is used to determine the maximum permitted earth fault loop impedance?
Zs ≤ Uo/Ia
Zs ≤ Ia/Uo
Zs ≥ Uo/Ia
Zs ≥ Ia/Uo
What is the minimum cross sectional area (csa) of a circuit protective conductor (CPC) when selected from the table below, if the live conductors are 25 mm2?
A. 6.0 mm2
A. 10 mm2
A. 16 mm2
A. 25 mm2
Which formula identifies the requirement for short-circuit protection of a cable?
A
B
C
D
Which method of installing a cable is permitted for the situation of buried in earth?
On a support wire
On insulators
On a Cable trunking
In a Cable ducting or conduit
Which area is not regarded as a medical location in the Saudi Building regulations?
Hospital waiting room
Surgery room
Examination or treatment room
Premature baby room
Which of the following earthing system is not allowed in medical locations and medical buildings downstream of the main distribution board?
TT
TN-C
TN-S
IT
When using SELV and/or PELV circuits as Protection against electric shock in medical locations of group 1 and group 2, the nominal voltage applied to equipment shall not exceed:
10 V a.c or 50 V d.c
220 V a.c or 500 V d.c
25 V a.c. or 60 V d.c
380 V a.c or 1000 V d.c
Which zone classified of Hazardous locations according to SBC 401 and SASO IEC 60079-10 where an explosive atmosphere is likely occur in normal operation occasionally?
Zone 0
Zone 1
Zone 2
Zone 3
One construction site is served by several sources of supply, which requirement need to apply?
Equipment must be identified for use of one particular supply
Connect the site with mobile power generators
Each supply must form part of a TN-S system
Supply must be protected by automatic disconnection
For electrical equipment installed in Zone 0 of a swimming pool, what degree of protection is necessary according to SBC 401 and SASO 980:
IPX8
IPX5
IPX4
IPX2
For swimming pool In Zone 2, socket-outlets and switches are permitted only if the circuits supplying them are protected by:
A residual current protective device with rated operating current not exceeding 30 mA
Miniature circuit breaker
Fuse box
Electrical on/off disconnect switch
In a location containing a bathtub or shower basin, which of the following is permitted in Zones 0, 1 and 2?
Junction boxes
Switchgear and control gear
Socket outlet with metallic covering
Waterproof recessed Ceiling light
In case of overhead distribution in camping sites, caravan and tents , what is the height above earth for overhead conductors in area subject to vehicle movement
At a height above earth not less than 6m
At a height above earth not less than 3.5m
At a height above earth not less than 2m
At a height above earth not less than 12m
What are the minimum Cross-sectional areas for line and PE conductor used in caravan or tent electrical installation according to Saudi Building Code?
Successively 1.5 and 2.5 mm square
Successively 1.5 and 4.0 mm square
Successively 2.5 and 2.5 mm square
Successively 4.0 and 4.0 mm square
According to SBC 401, the conductor for Phase 3 (L3) of three-phase a.c. circuit shall have the color of:
Brown
Gray
Blue
Black
As per SBC 401, the maximum operating temperature of Cross-linked polyethylene (XLPE) insulation is?
90oC
70oC
105oC
60oC
Where is Zone 2 located within a bathroom?
Interior of the bath tub or shower basin
The upper plane of Zone 0
Is the Vertical plane 0.6 m external to zone 1 and above zone 1 up to the ceiling.
Is the space above zone 2 up to the ceiling
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 ≤ In ≤ Ib
Which of the following laminations will form core type transformer?
L – L
E – E
E – I
E - U
Which of the following laminations will form shell type transformer?
L – L
U – I
E – I
E – U
What is the term used to know the change of output voltage from no-load to full-load
Efficiency
Voltage regulation
Voltage Drops
No-Load test
A transformer delivers 100 volts at no-load and the voltage drops to 95 volts at full load, so voltage regulation would be?
95%
5%
-5%
111%
1. What is the secondary current for a single-phase transformer which has a primary current of 60 A and a turns ratio of 2:1?
30 A
100 A
120 A
60 A
3-phase 12 poles, 60Hz induction motor has a rotor speed of 570 rpm, the slip is:
0.05%
4%
0.25%
5%
A universal motor is one that operates on:
Either single-phase ac or dc power.
DC power
AC power
Constant speed
At what speed three-phase cylindrical two-pole synchronous alternator rotates when connected to a 60 Hz infinite busbar system?
900 rpm
1800 rpm
3600 rpm
7200 rpm
Which Saudi building code relates to the installation of cables in buildings?
301
401
701
801
what color identifies the neutral conductor of a single-phase circuit?
Gray
Blue
Brown
Black
What is the classification of the area where an explosive gas is present?
Hazardous
Restricted
Dangerous
Confined
What is maximum nominal voltage for extra low-voltage?
24 V ac
24 V DC
50 V ac
50 V dc
What is the requirement for an underground wiring system if placed on a caravan pitch on a camp site?
Earth spike
Undervoltage protection
Dedicated isolator
Additional mechanical protection
What is the purpose of catenary systems?
To suspend cabling
To bury cabling
To cover cabling
To extend cabling
What details must appear on the nameplate of transformers rated above 500kVA?
Percentage impedance and frequency
Turns ratio and mutual inductance
Power factor and maximum current
Maximum current and turns ratio
Which formula determines the kVA rating of a three-phase transformer to supply a new building allowing for a 25% increase in demand?
A
B
C
D
Which formula determines the power transferred form the transformer primary to secondary winding in the image shown below?
P = Vp Ip cosθ
P = Vp (Ip-Io) cosθ
P = Vp Ip sinθ
P = Vp (Ip-Io) sinθ
What is the efficiency of a 200 kVA transformer having a copper loss of 1.5 kW and an iron loss of 1 kW with a power factor of 0.85? (Note the correct answer here is 98.55%)
96.60%
97.55%
97.65%
98.76%
What is the percentage impedance of the transformer shown in the image below?
5%
6%
8%
10%
What condition must be met for two transformers to share a load proportional to their VA rating when connected in parallel?
Load currents must be the same
Percentage impedances must be the same
Resistance of the windings must be equal
Power ratings of the transformers must be the same
What type of single-phase transformer is represented in the diagram below?
Current
Isolation
Auto
Voltage
What type of transformer is used in domestic appliances to charge batteries where is no direct electrical connection?
Current
Instrument
Induction
Auto
How many conductors (not contactors) are necessary to connect a three-phase induction motor in both Star and Delta?
3
4
6
7
Which load range indicates the maximum efficiency for an induction motor?
0 to 30%
35 to 40 %
60 to 80%
90 to 100%
How are the start and run windings arranged in a split-phase induction motor?
45 electrical degrees apart
90 electrical degrees apart
120 electrical degrees apart
180 electrical degrees apart
Which type of single-phase motor is most suitable for driving electric clocks?
Capacitor start
Split-phase
Capacitor run
Shaded pole
Why is the supply to the rotor of a series universal motor connected using brushes and a commutator?
To give a method of speed control
To allow operation on ac and dc
To allow the motor to reverse
To give a better power factor
Which action explains the operation of a phase protection relay in detecting the loss of one phase of the supply?
A higher current flow in the remaining phases heats the bi-metal trip mechanism
The hold in relay in the faulty phase trips to open the contactor
A detection of current imbalance by a current transformer trips the contactor
The voltage between the remaining phases increases, causing the contactor trip
1. Which types of rotor is used in an alternator designed for low-speed operation?
Cylindrical
Permanent magnet
Two pole
Salient pole
What is the most common fault when operating portable alternators?
Failure of prime mover
Brush gear failure
Failure in excitation
Bearing failure
What is an advantage of using terminal strips with links for cable connection in a control panel?
To assist fault-finding
To prevent faults occurring
To identify components
To improve earthing
What is the EMC purpose of earthing control panels?
To reduce the source of electromagnetic radiation
To filter the frequency output of a variable drive
To provide a ground connection for high-frequency cable shielding
To protect against electromagnetic radiated interference
What is the purpose of maintenance?
To keep plant in correct working order
To repair faults in failed equipment
To commission new plant
To increase downtime
Which type of maintenance is determined by using records of bearing failure and replacement?
Breakdown
Preventative
Corrective
Predictive
What is the effect on the maintenance plan if an item of equipment repeatedly fails between scheduled annual maintenance?
Maintenance intervals are decreased
Maintenance intervals are increased
Maintenance intervals are doubled
Maintenance intervals are unchanged
What is the purpose of detailing recommendations based on analysis of previous maintenance records?
To inform future requirements
To increase downtime
To reduce turnover
To inform on operative efficiency
What is the likely cause of a low value of insulation resistance on a single-phase motor?
It has been running on load
It has run overspeed
It has absorbed moisture
It has been overloaded
What will cause an RCD protecting a washing machine to trip?
Excessive runtime
Earth fault to the case
Fuse blown in the supply line
Short-circuit between line and neutral
What is the likely cause of failure of a newly installed compact fluorescent light when it is switched on?
It is controlled by a double pole switch
It is incompatible with a dimmer switch
The power rating is too low
The power rating is too high
What is a common cause of overheating in a three-phase motor?
The motor is on light load
The ventilation is poor
Intermittent earth fault
No load on the motor
What is indicated by a low insulation resistance between lines L1 and L2 of a star-connected stator of a three-phase motor?
Faulty insulation in phases 1 and 2
Faulty insulation in phase 1 or 2
Faulty insulation in all phases
Faulty insulation in any phase
What must be done to an approved voltage indicator immediately before its use?
It must be fully calibrated
It must be fitted with a shunt
It must be tested for insulation resistance
It must be checked against a known supply
Which conductors are combined at the origin of an installation as part of an MEN system?
L1 and N
PE and L2
PE and N
L1 and L2
1. What type of system uses MEN?
TT
TN-S
IT
TN-C-S
What is the purpose of an earth electrode in a TT system?
To ensure equipotential bonding
To protect against indirect contact
To make an effective contact with the mass of earth
To bring exposed conductive parts to the same potential
Which factor will effect the impedance of an earth fault loop path?
Type of insulation used
Change in the value of R
Type of overcurrent device used
CSA of the line conductor
Where must the value of R1 + R2 be measured on a circuit to calculate maximum earth fault loop impedance?
At the origin of the circuit
At the furthest point of the circuit
At each point of utilization
At the installation supply terminals
1. What condition must be satisfied to ensure co-ordination between protective devices and conductors?
Ib ≤ In ≤ Iz
Ib ≥ In ≤ Iz
Ib ≤ In ≥ Iz
Ib ≥ In ≥ Iz
what does an RCD provide protection against?
Earth leakage
Overload
Undervoltage
Overvoltage
What is the potential hazard of undervoltage for motor circuits?
Earth fault leakage
Excessive bearing wear
Circuit breaker failure to reset
Automatic restarting on supply restoration
What must be ensured before conducting the visual inspection of a new installation?
The installation is energized
The installation is isolated
All switches are in the ‘on’ position
All voltage sensitive devices are removed
What is the recommended maximum voltage drop between supply origin and equipment in a consumers’ installation?
2%
4%
6%
8%
What is included in the fundamental principles of ‘protection for safety’ in the Saudi building code 401?
Persons, livestock and property
Employees, livestock and property
Persons, switchgear and equipment
Employees, equipment and switchgear
Which method of protection against indirect contact detects earth leakage?
Extra-low voltage
Class II equipment
Electrical separation
Residual current device
What color is used to identify emergency switching devices?
Red
Blue
Green
Yellow
Which type of board is normally used to supply single-phase radial lighting circuits?
Main LV switchboard
Sub-distribution board
Final distribution board
Main HV switchboard
Why must creepage be considered at the design stage of a busbar system?
To prevent insulator tracking
To reduce voltage drop
To prevent high resistance
To reduce insulation thickness
Which is a type of telephone transmitter?
Dispersion
Chemical
Refractive
CapacItive
What is the main hazard when using polarized capacitors?
Sharp edges
Overheating
Leaking electrolyte
Toxicity
What is the main purpose of telecommunication cable surge suppression?
To dissipate unwanted heat
To improve data transfer rates
To reduce noise pickup
To reduce voltage transients
Which type of fixing device is used to attach telecommunication cables to a hard wall in a vertical shaft?
Ties
Tap
Cleats
Clips
Which type of tool is used to terminate Cat 5 cables?
Pressing tool
Compression tool
Setting tool
Crimping tool
