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WorksheetsAD REVIEW
Total questions: 248
Worksheet time: 2hrs 4mins
What type of switch is a manual single-pole single-throw (SPST) switch?
One way
Two way
Relay
Intermediate
What effect does an open circuit condition have on the current in a dc circuit?
Current increases
Current reduces
Current falls to zero
Current is unchanged
What is the power dissipated in a circuit carrying 2 A with an overall resistance of 100 Ω?
100 W
200 W
400 W
800 W
What process takes place when corrosion occurs in a metal?
Electrostatic change
Electrochemical change
Electromagnetic change
Electromechanical change
What type of cells converts chemical energy from a fuel into electricity through a chemical reaction with oxygen?
A fuel cell
An oxygen cell
A chemical cell
An electric cell
What happens to the resistance of a copper conductor if its temperature is increased?
It stays the same
It falls to zero
It increases
It decreases
A series circuit consisting of 100 μF and a resistor of 200 Ω is connected to a DC supply. What is the time constant of the circuit?
200 ms
100 ms
20 ms
10 ms
In the image below, A reads 5 A and V 10 V, what is the value of R2?
2 Ω
5 Ω
15 Ω
50 Ω
What is the purpose of an insulation resistance test on an electric drill after it is has been repaired?
To make sure the drill operates correctly
To make sure all electrical connections are tight
To confirm that the drill will not overheat when drilling
To confirm that the connections are not in contact with earth
Which fixed position power tool is used for sharpening a twist drill?
Belt sander
Angle grinder
Detail sander
Bench grinder
What is a connection method of operating a reed switch in an alarm circuit?
High temperature smoke surrounding the switch
Providing a magnet close to the switch
Provides heating near the switch
Providing a coil point
Why does a security panel have “zones”:
To provide access control
To permit admissible entry
To monitor areas at the same time
To be able to monitor areas individually
Why is it most important to keep the work area tidy?
To avoid trip hazards
To look more professional
To prevent damage to tools
To avoid damage to extension leads
What physical effect can be caused by long exposure to vibration when using a pneumatic drill?
Breathing difficulties
Increasing in blood flow
Severe pain and numbness in the hands
Stiffness in the upper legs and lower back
Which statement applies to the correct use of ladders?
A ladder can always be used a working platform
Only wooden ladders require inspection before use
An unsecured ladder may be used to access scaffolding
Three points of contact must always be maintained with the ladder
What is a hazard associated with working in a confined space?
Falling from a large tower scaffold
Poor oxygen levels make it difficult to breathe
Electric shock from a metal emergency stop button
Tripping over tools and work equipment on the floor
What is a common cause of electrical accidents?
Using a “permit to work” system to control electrical work
Working on equipment that has not been correctly isolated
Using competent people to carry out electrical work
Carrying out a risk assessment before work starts
Why is there a low risk of serious electric shock when a circuit operates at extra-low voltage (ELV)?
ELV produces small currents through the body
ELV produces high currents through the body
ELV circuits current give shocks to earth
ELV circuits are always isolated
What control measure is taken to confirm that a new insulation is safe before use?
All work is inspected and tested
Megger tests conform to international standards
All work has been carried out by skilled people
The designer has completed accurate calculations
What must a risk assessment process include?
Ensure people are properly trained
Ensure the work area is clean and tidy
Reducing the time to carry out an activity
Identification of hazards present during the activity
How can a sinusoidal voltage be generated in a single turn coil?
By rotating the coil in a uniform magnetic field
By rotating the coil in a rotating magnetic field
By rotating the coil along lines of magnetic flux
By rotating the coil across lines of magnetic flux
When is a current out-of-phase with a voltage?
When it opposes the voltage
When it has a different frequency to the voltage
When it reaches the peak value after the voltage
When it reaches its peak value at the same time as the voltage
What is the relationship between volt drop and current in a resistor?
V × I = R
V = I × R
V = I ÷ R
V = R ÷ I
How is the power factor of installation improved?
Connecting capacitors in parallel with the load
Connecting inductors in parallel with the load
Connecting capacitors in series with the load
Connecting inductors in series with the load
What is power factor in a circuit where the phase angle between current and voltage is ɸ?
Sin ɸ
Cos ɸ
Tan ɸ
Cot ɸ
What is one of the dangers of resonance in a series circuit?
No voltage across the capacitor
No current taken from the supply
Excessive volt drop across the resistor
Excessive current taken from the supply
What is the relationship between phase voltage (VP) and line voltage (VL) in a star connected three-phase alternator?
Vp = Z VL
VL = Z VP
Vp = √3 VL
VL = √3 VP
What machine will produce a balanced load when connected to a three-phase supply?
Capacitor start induction motor
Star-delta start induction motor
Universal motor
Shunt motor
What is an effect of high impedance in the neutral conductor of a three-phase four-wire system supplying an unbalanced load?
Increased voltage on the line conductors
Reduced voltage on the line conductors
Increased voltage at the neutral point
Decreased voltage at the neutral point
What produces lagging reactive power in a three-phase system?
Inductance
Resistance
Capacitance
Conductance
What is the expression for impedance in a series circuit derived from the right angled triangle?
Z2 = R2 – X2
Z2 = R2 ÷ X2
Z2 = R2 × X2
Z2 = R2 + X2
What is the volt drop in a conductor with a resistance of 0.03 Ω, inductive reactance 0.04 Ω and impedance 0.05 Ω carrying 50 A?
1.5 V
2.0 V
2.5 V
3.0 V
Which type of diagram and lighting system is shown in the image below?
Wiring diagram with loop at light
Current diagram with loop at light
Wiring diagram with loop at switch
Current diagram with loop at switch
What is the minimum mounting height for a socket outlet above a kitchen workshop?
100 mm
200 mm
300 mm
400 mm
Which method of heat transfer is shown in the image below?
Induction
Radiation
Conduction
Convection
Which describes the basic operation of a UPS system?
The main supply feeds the load when the UPS fails
When the load increases, the UPS acts as a booster
The UPS supplies the load when the main power supply fails
The UPS supplies the load at the same time as the main power supply
What would be the specific gravity of the electrolyte in a fully charged lead-acid cell?
1.19
1.22
1.25
1.28
Which section of the Saudi Building Code requirements relates to fire protection?
Section 201
Section 401
Section 601
Section 801
What is the basic operating principle of an incandescent lamp?
Current in a filament makes a white glow
Voltage produces a discharge in a gas
Current passes through a gas
Voltage produces an arc
Which type of lamp is shown in the circuit diagram?
Low pressure sodium
High pressure sodium
Low pressure mercury vapor
High pressure mercury vapor
What would be a typical application for a Xenon lamp?
A street light
A security light
A shower room
A cinema projector
What are the main reasons for dividing an installation into a number of circuits?
To increase installation time and decrease complexity
To simplify fault finding and improve circuit protection
To maintain the size and number of conductors
To simplify inspection and testing
Which relationship will ensure that cables are protected against overload?
Ic × Ip = Il
Ic × Ip ≤ Il
Ic ≥ Ip ≥ Il
Ic ≤ Ip ≤ Il
What is the ambient air temperature at which the current carrying capacities of PVC cables in air are given in the Saudi Building Code 801?
20°C
25°C
30°C
35°C
Which multi- core cable installation method will allow the highest conductor current carrying capacity?
a
b
c
d
What is a requirement for isolation for a TN-C system?
PEN conductors must always be isolated
PEN conductors must not be switched or isolated
PEN conductors must be isolated after the phases
PEN conductors must be isolated before the phases
What is the advantage of using a standard terminal labeling system on relay circuits?
To allow ease of circuit installation
To make control circuit drawings simpler
To allow easy identification of conductors
To ensure all conductor sizes are the same
What type of diagram is used to show the operation of programmable controllers?
Schematic
Wiring
Layout
Ladder
What is a reason for limiting the starting current of large three-phase induction motors?
To allow a progressive soft start
To prevent single phasing
To prevent over-speeding
To limit local volt drops
What is the braking system that converts mechanical energy into electrical energy?
Plug
Dynamic
Eddy current
Regenerative
What is the effect of a step down transformer in a distribution system?
Reduce voltage and reduce current
Increase voltage and reduce current
Reduce voltage and increase current
Increase voltage and increase current
What is the direction of electron flow in a coil of wire connected to a dc supply?
Clockwise round the coil
Anticlockwise round the coil
From positive to negative around the circuit
From negative to positive around the circuit
What is the ratio of flux density (B) to magnetizing force (H) in a magnetic circuit?
Permeability
Reluctance
Permittivity
Resistance
What equipment uses the principle of mutual inductance?
Overhead transmission line
Underground cable
Alternator
Transformer
Which quantity is not measured using a dynamometer instrument?
Power
Current
Voltage
Resistance
What are the units for the continuous rating on the nameplate of a large three-phase induction motor?
kW
kVA
kVAR
kWh
What type of dc generator relies on residual magnetism to produce a voltage?
Shunt excited
Series excited
Separately excited
Continuously excited
What relationship defines torque when force (F) is produced by a shaft of radius (r) rotating at speed (n)?
T = n × F
T = r × F
T = F ÷ n
T = F ÷ r
What are the mechanical losses produced by a dc motor when it is rotating?
Friction and windage losses
Copper losses
Iron losses
Eddy current and hysteresis losses
What is the magnetomotive force (mmf) produced by a 200 turn coil carrying 2 A from 6 V supply?
200 A
400 A
1200 A
2400 A
How is the armature in a dc generator connected to an external circuit?
Through slip rings
Through a resistor
Through a commutator
Through a fixed contact
What current does a short circuit produce?
Zero current
Steady current
Overload current
Excessive current
What is the relationship between Work and Force?
Force = Work x Time
Force = Work ÷ Time
Work = Force ÷ Distance
Work = Force x Distance
What effect produces a force of attraction when current is passed through a relay coil?
Heating
Magnetic
Radiation
Chemical
What process does a fuel cell use to produce electrical energy?
Heat reaction
Magnetic action
Chemical reaction
Photovoltaic action
What is the function of a potentiometer?
To produce a magnetic field
To provide variable voltages
To provide a heating element
To add fixed resistance into a circuit
What is the relationship for stored energy in a capacitor?
½ CV2
2 CV2
½ C2V
2 C2V
A voltmeter across a load reads 100 V and an ammeter indicates a load current of 2.5 A. What is the resistance of the load?
25 Ω
40 Ω
250 Ω
400 Ω
Which statement describes the correct procedure when terminating cables?
Insulation is removed using pliers
Leave 20 mm of exposed bare conductor at a termination
All strands of a conductor do not need to enter an electrical connection
Green/yellow insulation must cover bare protective conductors at terminations
Which safety precaution must be taken when using a bench grinder?
The wheel must run for one minute before use
Goggles only need to be worn for grinding steel
The wheel must rotate freely before switching on
The rest must be at least 10 mm away from the wheel
What modification is required to the circuit below so that an open circuit wiring fault can be detected by the alarm panel?
Add a resistor in series with the existing resistor
Add a resistor in parallel with the contact
Change the contact to normally open
Change the value of the resistor
What type of panel to remote base communication is used by security systems?
Pulse Code Modulation to Frequency Division Multiplex
Public Service Telephone Network to Ethernet
Digital to analogue
Analogue to digital
What is the correct procedure for lifting an object?
Walk quickly to reduce carrying time
Assess the weight before lifting
Carry with one hand using a handle
Keep feet close together on firm ground during lifting
What is not an effective way to protect against ultraviolet (UV) radiation from sunlight?
Drink water to keep hydrated
Apply a suitable barrier cream
Wear clothing that covers the body
Wear sunglasses when working outside
What is the main safety measure to take before moving a scaffold tower?
Toolboxes are secured
Outriggers are in position
All connecting bolts are tightened
Check there are no overhead obstructions before moving it
What location would be classed as a confined space?
A high voltage switch room
A store room in an office
An enclosed cable duct
An outdoor substation
What type of protection does a 30 mA RCD provide?
Overload
Additional
Short circuit
Overcurrent
What item of equipment is not to be supplied from an extra-low voltage supply?
A motor control circuit
A hand-held inspection lamp
Underwater lighting in a pool
A three-phase induction motor
What is the risk of adding too many circuits to an existing electrical installation?
The new circuit does not meet regulations
The circuit breaker is not matched to the load
The new circuit may cause the existing installation to overload
The additional circuit is the longest circuit on the installation
Which statement best describes how to assess the level of risk?
Consider the likelihood of someone being harmed and the type of resulting injury
Investigate accidents and change working procedures to avoid it being repeated
Establish a "near miss" reporting system
Identify the hazards and issue PPE
How are the values of sinusoidal alternating currents normally expressed?
As an rms value
As a peak value
As an average value
As an instantaneous value
What is the purpose of a phasor diagram?
To show periodic time
To show current wave shape
To show elements in the impedance triangle
To show the angle between voltage and current
What is the ratio of voltage to current in an ac circuit with an iron cored coil of negligible resistance?
Impedance
Self-inductance
Mutual inductance
Inductive reactance
What is required to improve the power factor of an induction motor?
An inductor conducted in series
A capacitor conducted in series
A capacitor connected in parallel
An inductor connected in parallel
What unit is used for measuring apparent power in an ac circuit?
kVA
kVAr
kAh
kW
What is one condition for resonance in a parallel ac circuit containing resistance (R) inductance (L) and capacitance (C)?
IL = IC
IL = IR
IL = 0
IC = 0
How are three phase voltages generated in one alternator?
By using three stator coils separated by 120º
By using three stator coils separated by 60º
By using three magnetic fields separated by 120º
By using three magnetic fields separated by 60º
What is the relationship between phase current IP and line current IL in a balanced delta-connected load in a three phase circuit?
IP = IL x 1.73
IP = IL ÷ 1.73
IP = IL + 1.73
IP = IL – 1.73
The line currents in a three phase four-wire system are IBr IBl and IG. What expression gives the current IN in the neutral conductor?
IN = IBr – IG + IBl
IN = IBr + IG – IBl
IN = IBr – IG – IBl
IN = IBr + IG + IBl
What is the purpose of measuring the power factor of ac power systems?
To use more power
To increase the reactive power
To identify the phase angle between true power and apparent power
To increase the phase angle between true power and apparent power
What is the frequency of a sinusoidal voltage with a periodic time of 16.7 ms?
16.7 Hz
60 Hz
167 Hz
600 Hz
What is the impedance of a coil of wire with a resistance of 12 Ω and a reactance of 5 Ω?
5 Ω
8 Ω
12 Ω
13 Ω
Which test verifies that a one-way lighting switch is connected in the phase conductor?
Polarity test
Functional test
Insulation resistance test
Test for electrical separation
What is the minimum insulation resistance for a circuit rated at 220 V?
0.25 MΩ
0.5 MΩ
1.0 MΩ
1.5 MΩ
What is the heat energy produced by an element supplied at 220 V carrying 5 A for 300 s?
330 J
1100 J
330 kJ
1100 kJ
What is the main reason for installing an alternative supply system?
To reduce energy costs
To stabilize the voltage
To act as a booster at peak times
To ensure essential equipment always operates
What is used to identify the state of charge of a secondary cell?
Manometer
Hydrometer
Thermometer
Dynamometer
Which connection arrangement for the detectors of a fully addressable fire alarm system is correct?
The same detector type must be used in each zone
Any detector can be connected on any zone
The detector wiring will determine the zones
No detector zoning is required for the installation
Which color rendition is associated with a gas filled tungsten filament lamp?
Good in the red light spectrum only
Poor in the blue light spectrum only
Good over all the light spectrum
Poor over all the light spectrum
What is the typical efficacy range of a compact fluorescent lamp?
10 - 20 lm/W
40 - 60 lm/W
80 - 100 lm/W
120 - 180 lm/W
Which type of lamp produces the highest lumens per watt output?
Low pressure sodium
High pressure sodium
High pressure mercury
Low pressure mercury
Which external factor will damage a TPS cable installed at high level clipped to the outside of a building?
Wind
Corrosion
Solar radiation
Mechanical impact
What is used to maintain the fire rating of a building with a plasterboard partition when cables pass through it?
Fire foam
Fire blanket
Sand barrier
Silicone sealant
What information about conductors must be recorded on a distribution board circuit schedule?
Color and size
Number and size
Size and material
Number and color
Which installation method has the highest derating factor for power cables?
In free air
In trunking
Clipped direct
Embedded in insulation
What is a general requirement for isolation within an electrical installation?
Every circuit must have means of isolation
Essential circuits only require means of isolation
Non-essential circuits only require means of isolation
A single means of isolation at the origin is acceptable
What type of contact is the jogging button on a motor starter?
Normally open
Normally closed
Make before break
Break before make
What type of relay would be used to automatically control a production line?
Reed
Bi-polar
Latching
Programmable
Which type of motor starter offers continuous and smooth acceleration?
Soft starter
Star delta starter
Direct on line starter
Autotransformer starter
What is the operating principle of a variable frequency drive of a synchronous motor?
Load current is proportional to frequency
Speed is directly proportional to frequency
Supply voltage is proportional to frequency
Speed is inversely proportional to frequency
Why are high voltages used for transmission systems?
To increase currents in the conductors
To reduce conductor sizes
To reduce insulator sizes
To improve safety
What magnetic device assists in extinguishing an arc in a circuit breaker?
Arc chute
Arc runner
Arc blow out coil
Arc splitter plate
What factor from a hysteresis loop for a magnetic material is directly related to energy loss?
Residual flux
Area of the loop
Maximum flux density
Maximum magnetizing force
What factor determines the inductance of an iron cored coil?
Resistance of the coil wire
Number of turns on the coil
Frequency of applied voltage
Insulation resistance of the coil
What is a moving coil instrument used to measure when fitted with a multiplier?
Alternating voltage
Alternating current
Current in a dc circuit
Voltage in a dc circuit
What maintenance procedure improves the operation of the commutator on a dc machine?
Lubricating the commutator surface
Moving brushes round the commutator
Undercutting the commutator insulation
Interchanging brushes around the commutator
What quantities are required to produce the load characteristic of a dc shunt generator?
Emf and output current
Emf and armature current
Terminal voltage and output current
Terminal voltage and armature current
Why will a series motor over speed when on no load?
The flux is too high
The flux is too low
The armature current is too high
The armature voltage is too low
What conditions are required to give maximum efficiency in a dc machine?
There are no copper or iron losses
The machine runs at constant speed
The machine runs with full load current
Variable losses and fixed losses are equal
What is the output power used by a motor developing 50 N-m at 1500 rev/min?
7.85 kW
78.5 kW
785 kW
7850 kW
What is the effect when electrons collect on the surface of an insulating material due to friction?
Current electricity
Chemical charge
Magnetic charge
Static electricity
What condition is needed for a circuit breaker to operate to open the circuit?
No load
Short circuit
Normal load
Open circuit
Which units are used to determine electrical power in Watts?
Newton/second
Joules seconds
Joules/second
Newton seconds
What mechanism causes metals to corrode?
Chemical reaction
Magnetic reaction
Photovoltaic reaction
Electrostatic reaction
What is the effect of moving a single length of conductor at right angles through a magnetic field?
Current is produced
Heat is produced
Force is produced
EMF is produced
Four 1.5 V cells are connected in parallel. What is the voltage when measured at the terminals of the combination?
1.5 V
3.0 V
6.0 V
7.5 V
Four 1.5 V cells are connected in series. What is the voltage when measured at the terminals of the combination?
2 V
4 V
6.0 V
7.5 V
After what period is a capacitor considered to be fully charged when connected to a battery?
One second
Five seconds
One time constants
Five time constants
What is the unit to measure the quantity of electricity or (quantity of electric charge)?
Volt
Joule
Ampere
Coulomb
Which statement is correct in relation to the soldering process?
Solder flux must be used during soldering to prevent oxidation
The tip of the soldering iron must glow red so that it will melt the solder
A heat sink is used during soldering to prevent the solder getting too hot
Silver solder can be used when soldering electronic components to a circuit board
What must be checked when setting up a pedestal grinder to perform off-hand grinding?
The grinding wheel is new and correctly fitted and tight
The grinder rest is positioned to prevent the work piece from jamming
The grinder visor has been removed if the user is wearing goggles
The grinder rotates at a speed greater than that shown on the grinding wheel
What does an end of line resistor connected in series with a normally closed call point do?
Helps to prolong battery life
Prevents short circuit currents
Allows the control panel to detect a short circuit on the wiring
Prevents the control panel from detecting an open circuit in the wiring
What is the supply arrangement for a security system?
Rectified ac supply
Primary cell battery
Rectified ac supply with back up battery
High voltage supply with back up battery
Which PPE is worn in a noisy environment to protect against damage to hearing?
Hard hat
Ear defenders
Safety goggles
Protective gloves
Which is a classification of a hazardous substance?
Vapor
Fume
Toxic
Gas
What is a safety check that must be carried out on a wooden ladder before use?
Check for splits in the wood
Check the wooden uprights a painted
Check the ladder is fitted with rubber feet
Check the length of the ladder
Which would be classified as a "confined space"?
A switch room
A substation
An air duct
An office
What is the best method of reducing risk when carrying out maintenance on an electrical installation?
Only work on single-phase circuits
Place a notice on the local isolator
Switch off the local isolator
Safely isolate and lock off
What is the voltage range of a 33/13.8 KV transformer?
Extra Low
Medium
High
Low
What control procedure is applied when working on a circuit in an industrial installation?
Place a notice on the local isolator
Switch off the Local isolator
Notify the energy supplier
Issue a permit to work
What is the first control measure to be considered when minimizing risk?
Stop the activity
Barrier of a safe area
Redesign the equipment
Wear personal protective equipment
What is the period of a sinusoidal ac waveform?
The time taken to complete one cycle
The time taken to reach maximum value
The time between two successive zero values
The time taken between positive and negative maxima
What does the term "lag" means when voltage V1 lags V2 by 90 degrees?
V2 reaches its maximum value a half cycle after V1
V1 reaches its maximum value a half cycle after V2
V2 reaches its maximum value one quarter after V1
V1 reaches its maximum value one quarter after V2
What does the term "lag" means when voltage V1 lags V2 by 90 degrees?
V2 reaches its maximum value a half cycle after V1
V1 reaches its maximum value a half cycle after V2
V2 reaches its maximum value one quarter after V1
V1 reaches its maximum value one quarter after V2
For a given real power output, what is the effect of low power factor?
low voltage
low current
high current
high voltage
What is the relationship for power factor in a single phase circuit?
Pf = I / V
Pf = kW / kVA
Pf = V / I
Pf = kVA / kW
What is the second harmonic of an AC waveform having a fundamental frequency of 60 Hz?
30 Hz
60 Hz
90 Hz
120 Hz
What is the correct phase sequence of a three phase generator when V1 reaches maximum voltage before V2 and after V3?
V3, V1, V2
V1, V3, V2
V2, V1, V3
V3, V2, V1
What is necessary for a balanced load in a three-phase system with star-connected loads?
Phases have different loads and the same power factor
Phases have load currents in phase with their voltages
Phases have the same current and power factor
Phases have power factors that total zero
What is the relationship between line current IL and phase current IP in a delta connected load in a three-phase system?
Iline=IPhase
Iline =√3∗Iphase
IPhase =√3∗Iline
IPhase =√2∗Iline
What is measured to determine how much electricity a consumer has used?
Energy
Power
Power factor
Maximum demand
What is the RMS value of a sinusoidal alternating voltage with a peak value of 100 V?
63.7 V
70.7 V
141.4 V
157.2 V
What is the inductive reactance of a coil with a reactance of 100 mH when the supply frequency is 50 Hz?
3.14 Ω
6.28 Ω
31.4 Ω
62.8 Ω
Which type of diagram and lighting system is shown in the image below?
Wiring diagram with loop at light
Current diagram with loop at light
Wiring diagram with loop at switch
Current diagram with loop at switch
What is the minimum cross sectional area for copper conductors supplying 220 V, 13A socket outlets in a residential bedroom?
6 mm2
4 mm2
2.5 mm2
1.5 mm2
A 1.5 KW electric heater switched on for one hour, what will be the energy consumed?
90 MJ
5.4 MJ
90 KJ
5.4 KJ
What is the correct connection for an inverter in an “on-line” UPS
Bypassed during normal use
Connected to the load at all times
Bypassed when the normal supply fails
Connected only when the normal supply is fails
What will be the terminal voltage of a fully charged nickel cadmium cell?
2.1 V
1.7 V
1.5 V
1.2 V
What is the purpose of the radioactive source in a smoke Alarm?
To repel smoke particles
To attract smoke particles
To provide a high resistance within the detector
To provide a constant current flow within the detector
What is the source of light in an incandescent lamp?
An electrical discharge
A white hot filament
Mercury vapor
Sodium vapor
Which type of lamp is shown in the circuit diagram?
Low pressure sodium
High pressure sodium
Low pressure mercury vapor
High pressure mercury vapor
What type of driver is used to supply a led lamp made up of a number of single LED’s connected in parallel?
Constant voltage
Lagging voltage
Constant current
Leading current
Which type of contact occurs as the result of a fault on an electrical circuit?
Accidental
Intentional
Indirect
Direct
What is the requirement of a protective conductor when a fault to earth occurs?
To reach an excessive temperature
To carry the expected fault current
To break a circuit within a fired time
To disconnect the supply under fault conditions
What is the reason for dividing an installation into a number of circuits?
To increase the installation time
To increase the CSA of the conductors
To minimize the requirements for control gear
To minimize inconvenience in the event of a fault
The live conductors of a 220 V circuit have a total combined resistance of 0.3 ohm at normal operating temperature and carry a load current of 25 A. What is the voltage drop across the conductor?
83 V
66 V
8.8 V
7.5 V
What method can be used to provide protection against indirect contact?
Using enclosures
Using double insulation
Using CIass1 equipment
Using a SELV supply at 25 V
Which type of relay can operate on full load and under short circuit conditions?
Overload
Polarized
Contactor
Latching
What is the purpose of the jogging control button on a motor starter?
To rotate the motor when operated
To override the start button
To override the stop button
To replace the stop and start buttons
What type of motor starter would be used to reduce the starting current of a large three-phase squirrel cage induction motor?
Rotor resistance
Direct on line
Multi speed
Star-Delta
What is the method of braking a three-phase induction motor by putting the motor into reverse?
Plug braking
Dynamic braking
Regenerative braking
Eddy current braking
What equipment is required to step-up voltages in a high voltage transmission system?
Isolator
Regulator
Generator
Transformer
What law determines the production of an emf in a magnetic field?
Faraday’s Law
Ampere’s Law
Henry’s Law
Ohm’s Law
What is the unit of magnetic flux?
Farad
Henry
Weber
Siemen
What does Lenz's Law determine?
The magnitude of current set up by an induced emf
The direction of current set up by an induced emf
The magnitude of an induced emf
The direction of an induced emf
Which quantity would be measured by a dynamometer instrument?
Force
Torque
Electrical power
Electrical resistance
Which component of a DC machine ensures that the voltage output acts in one direction only?
Yoke
Armature
Brush gear
Commutator
What is the function of the prime mover in a turbine driven alternator?
To rotate the generator
To supply the generator flux
To convert mechanical energy to electrical energy
To convert electrical energy to mechanical energy
What is a method of reversing the direction of rotation of a dc shunt motor?
Interchanging the inter poles
Interchanging the supply terminals
Reversing the armature connections
Reversing the armature and field connections
What is a source of energy loss in a dc motor?
Over speeding
Winding resistance
Stray electrostatic fields
Supply voltage fluctuations
What is the power output of a motor with a torque of 50 Nm rotating at 1500 rpm?
47.1 kW
75 kW
470 kW
7.86 KW
What condition is needed for a DC circuit breaker to operate to open the circuit?
No load
Short circuit
Normal load
Open circuit
RCD are designed to quickly and automatically disconnect a circuit when the electric current is not balanced between:
Line & Neutral
Line & Ground
Line & Earthing
Neutral & Ground
When metals (iron & steel) are exposed to air, it reacts with oxygen then corrosion occurs in the presence of:
Two metals
Moisture
Dioxide carbon
Electrons
A transformer with an input power of 500 K.W and losses power of 20 K.W, what is the efficiency of transformer?
92%
90%
96%
85%
Electrical energy in a 'resistive' circuit converts energy into?
Chemical energy
Reverse polarity
Magnetism
Heat
What material is used in the construction of low-power resistors used in many electronic circuits?
Carbon
Silicon
Germanium
Aluminum
The below safety sign refer to?
Non-flammable non-toxic gas
Toxic material
Non compressed gas
Flammable liquid
For the diagram shown below, which one of the following statements is true?
V2 leads V1
V1 leads V2
V1 lags V2
V1 in Phase with V2
What will be the value of a capacitor in farads when it has a capacitive reactance of
200Ω and is connected to a 50Hz supply?
15 μF
15.92 μF
62.8 KF
10 KF
For the diagram shown below, which one of the
following statements is true?
Current lags voltage by 900 in phase
Voltage leads current by 00 in phase
Current leads voltage by 00 in phase
Voltage lags current by 900 in phase
An inductor connected in series with a resistor to an a.c. supply, will cause the:
Current to lag the voltage
Power efficiency improve
Voltage to lag the current
Power factor to approach
The incandescent lamps usually are filled with an inert gas mixture consisting primarily of
oxygen
argon
carbon dioxide
helium
The light switch wiring in the figure, is about controlling a lamp by
Two way switching (3 wire control)
One way switching
Two way switching (2 wire control)
Three way Intermediate switch wiring
A series circuit consisting of 200 μF and a resistor of 200 Ohm is connected to a DC supply. How much time the capacitor will take to be fully charged?
0.2 s
0.4 s
40 s
4 s
The maximum allowable voltage drop of a cable as per the Saudi Building code 401 is (Vs=220V) :
8.8 V
6.6 V
9.2 V
4.8 V
Which type of protection is provided for electrical motor against overheating?
Over Voltage Protection
Over-Load Protection
Short Circuit protection
No Load Protection
The direction of rotation of dc series motor can be reversed by interchanging ___ terminals:
Armature
Supply
Field
Either Armature or Field
What does Len'z law determine?
The direction of current set up by an induced EMF
The direction of an induced EMF
The magnitude of current set up by an induced EMF
The magnitude of an induced EMF
The function of ____ in dc generator is to collect current from commutator and deliver it to external circuit
End rings
Dummy Coils
Brushes
Equalizer rings
In an Iron Cored coil, the Iron core is removed so that the coil becomes an air cored coil. The inductance of the coil will:
Increase
Decrease
Remain the same
Initially increase and then decrease
Identify the correct symbol for the ampacity of the cable.
In
It
Iz
Ib
What is steel wire used for in electrical distribution cable?
Live conductors
Insulation
Outer sheath
Armor
What the purpose of a circuit breaker in a DC circuit?
To protect against high voltage
To limit current flow
To protect against over-current
To limit voltage drops
What power is dissipated in a heating element with a resistance of 5 Ohm if the volt drop across the element is 50V?
75W
125W
250W
500W
What is the main physiological effect when receiving an electrical shock?
Joint swelling
Muscle spasm (Contraction)
Nausea
Dysfunction
What term is used when a mechanical force applied to a crystal generates e.m.f?
Thermoelectric effect
Electro-mechanical effect
Electro force effect
Piezoelectric effect
What is the effect on the output of connecting cells in parallel?
Increased terminal voltage
Increased current capacity
Reduced current capacity
Reduced terminal voltage
What is the effect on the value of a capacitor if the plate area is doubled?
Double the capacitance
Half the capacitance
Double the working voltage
Half the working voltage
What is the effect on the value of a capacitor if the distance between plates is doubled?
Double the capacitance
Half the capacitance
Double the working voltage
Half the working voltage
What is the effect on the value of a capacitor if both area and distance of separation are doubled?
Double the capacitance
Half the capacitance
Capacitance value would remain the same
Half the working voltage
What are the voltage supplied to a circuit which has 2 Ohm and a 10 Ohm resistor connected in series when the volt drop across the 2 Ohm resistance is measured at 10 V?
10 V
20 V
40 V
60 V
Why is the armor on steel wire armored cables secured in a termination gland?
To stop ingress of moisture
To meet fire regulation
To prevent stress on conductors
To protect the cable sheath
On what part of the offhand grinder is the work placed during the grinding operation?
Wheel guard
Wheel axis
Tool rest
Guide Block
What is the standard resistance range used for end of line resistors in security alarm circuits?
0.1 Ω - 1.1 Ω
1.5 Ω - 2.7 Ω
1 KΩ - 22 KΩ
220 KΩ - 2.7 M Ω
What is the purpose of a dialer in an alarm system?
To provide panel to discrete sensor communication
To provide sensor to sensor communication
To provide wireless co-ordination of all alarm sensors
To provide panel to remote user communication
Which item of PPE must be worn when sharpening a drill bit using a grinder?
Safety boots
safety helmet
Safety Goggles & Glasses.
Safety Harness
What does the labeling symbol in the image below identify?
Carcinogenic
Acute toxicity
Oxidizing gazes/liquid
Flammable gases/liquid
What is purpose of a toe board on a scaffold system?
To provide additional structural rigidity
To prevent people falling of the platform
To prevent tools and equipment falling off the platform
To physically define the hatch on a scaffold platform
Which control measure gives authority to enter a confined space?
Method statement
Risk assessment
Permit to work
Specific PPE
Which device minimizes the risk of electric shock through direct contact?
High rupture capacity fuse
Residual current device
Circuit Breaker
Isolator
Which device enables the step-down of voltage in an electrical distribution system?
Pylon
Transformer
Busbar
Isolator
What does a barrier provide protection against within a consumer control unit?
Direct Contact
Indirect Contact
Earth Fault
Short Circuit
What is the main purpose of risk management?
To control risks
To document risks
To provide staff training
To provide appropriate PPE
What value I defined by 0.707*peak signal in sinusoidal waveform?
Period
Average
Instantaneous
Root mean square
What is the meant by the term in phase in relation to sinusoidal voltage and current waveforms?
The voltage waveform leads the current waveform by 900C
The voltage waveform lags the current waveform by 900C
The two waveforms are separated by 1800C
The two waveforms are separated by 00C
What is defined by the formula XL=2πfL?
Real power
Reactive power
Inductive reactance
Capacitive reactance
What effect does adding capacitance have on a purely resistive circuit?
Voltage lags current by 900C
Voltage leads current by 900C
Voltage lags current by 1800C
Voltage leads current by 1800C
Which value is measured in Watts?
Apparent power
Power factor
Reactive power
True power
Which component produces harmonics in an AC system?
Resistive heater
Fluorescent lamp
Linear power supply
Smoothing capacitor
Which component not produces harmonics in an AC system?
Resistive heater
Electronic Ballast
Variable speed drive
Welding machine
What the meaning of the term phase sequence?
The order of phase waveforms in a poly-phase system
The phase displacement between phases
The amplitude of each phase voltage and current
The phase relationship between voltage and current
What is the nominal line voltage of a three phase star-connected system if the phase voltage is 230V?
110V
230V
400V
600V
Which conductor in a three phase TT system only carries unbalanced load current?
Earth
Line
Phase
Neutral
What is the purpose of measuring and correcting the power factor?
To improve the electrical efficiency
To decrease machine speed
To check the electrical safety of the system
To increase machine speed
What is the length of the hypotenuse of a triangle when the lengths of the other two sides are 10.4 cm and 27.2 cm?
16.8 cm
25.13 cm
29.12 cm
37.6 cm
What is the value of capacitance reactance for a circuit with a frequency of 60 Hz and a capacitance of 22μF?
60.35 Ω
120.57 Ω
427.38 Ω
757.57 Ω
What must be checked as part of an insulation resistance test on a two way lighting circuit?
The wiring in both “on” switch positions
The contact rating of the switch
The correct color code sleeving has been applied
The CPC is the same size as the live conductors
What installation method is suitable for an external socket outlet circuit wired in non-armored conductors and subject to potential mechanical impact?
In PVC Trunking
On a cable ladder
On perforated steel tray
In galvanized steel conduit
What function does a UPS system provide?
Three-phase power factor correction
Back up in the event of a mains power failure
Increased equipment power efficiency
Star-Delta starting of a three phase motor
What gas must be ventilated when charging secondary cells?
Nitrogen
Hydrogen
Argon
Helium
What type of alarm is shown in the image?
Rate of rise
Optical
Ionization
Carbon monoxide
What type of circulatory heat transfer is shown in the image?
Convection
Conduction
Infrared radiation
Electromagnetic radiation
What is the expected lamp life for a typical incandescent lamp?
200 Hours
1200 Hours
10000 Hours
50000 Hours
What is the function of ballast unit for a high intensity discharge lamp?
To limit current
To amplify voltage
To Attenuate voltage
To smooth current
What type of operating technology does an LED use?
Semiconductor
Resistive
Capacitive
Inductive
What term defines the variation of the load current of an installation over a period of time?
Volt drop
Diversity factor
Temperature co-efficient
Grouping factor
What method of protection is acceptable for fixed equipment that may get hot enough to become a fire hazard?
Only mount the equipment outside a building
Only use a fire rated cabling and containment systems
Screen with high temperature capable materials with low thermal conductance
Screen with low temperature capable materials with high thermal conductance
