“150”, Aptitude Test Questions and Answers for Artisan Grade II (Electrical) – TANESCO.
ABSTRACT
This aptitude test preparation guide
contains 150 multiple-choice questions and answers designed for candidates
applying for the position of Artisan Grade II – Electrical at the Tanzania
Electric Supply Company Limited (TANESCO). It covers essential electrical trade
knowledge, including electrical installation, electrical measurements, motor
operation, transformers, circuit protection, fault diagnosis, preventive
maintenance, and electrical safety. Each question is accompanied by a correct
answer and an explanatory rationale to help candidates understand key technical
concepts and apply them to practical workplace situations. The guide aims to
strengthen candidates’ technical knowledge, problem-solving skills, and
confidence in preparing for aptitude tests. It serves as a revision resource to
support effective preparation for recruitment assessments and the practical
responsibilities associated with electrical maintenance work.
Prepared for: Candidates applying for
Artisan Grade II (Electrical) – TANESCO
Independent aptitude-test preparation
resource; not an official TANESCO publication.
0628729934.
Date: October 29, 2026
Dear applicants,
This collection of 150 multiple-choice
questions and answers is designed to help candidates revise electrical trade
knowledge relevant to aptitude tests and recruitment assessments for Artisan
Grade II (Electrical) – TANESCO. It is an independent preparation resource, not
an official TANESCO examination paper, and it does not guarantee that any
question will appear in a recruitment assessment. I wish you success in your
preparation and recruitment process!
Warm regards,
Artisan Grade II (Electrical) – TANESCO
Aptitude Test Preparation Guide
Independent aptitude-test preparation
guide for candidates applying for Artisan Grade II (Electrical) – TANESCO. Not
an official TANESCO publication.
Artisan Grade
II (Electrical) – TANESCO.
150 Aptitude
Test Questions and Answers
Question 1
During preventive
maintenance of a distribution panel, an artisan discovers that a circuit
breaker trips repeatedly after operating for approximately 20 minutes under
normal working conditions. The connected equipment appears to function normally
before the breaker trips. Which action would provide the most useful initial
evidence for determining the cause of the repeated tripping?
A. Measure the
circuit current under operating conditions and compare it with the protective
device rating and expected load. B. Replace the circuit breaker with one of a
higher current rating and observe whether the circuit remains operational. C.
Disconnect the protective earth conductor temporarily and check whether the
circuit breaker continues to trip. D. Tighten all accessible terminals
immediately and restore the circuit without recording the initial operating
conditions.
Answer: A.
Measure the circuit current under operating conditions and compare it with the
protective device rating and expected load.
Rationale: Measuring the operating current and
comparing it with the circuit breaker's rating is an appropriate initial
diagnostic step because repeated tripping after a period of operation may
indicate sustained overload, excessive equipment demand, or another condition
that causes the protective device to operate as it heats up. The measurement
helps establish whether the current exceeds the expected operating range and
guides subsequent investigation. Replacing the breaker with a higher-rated
device without verifying conductor capacity and circuit design could leave the
circuit inadequately protected. Disconnecting the protective earth conductor
would create a dangerous condition and would not establish the cause of
ordinary overcurrent tripping. Tightening terminals may eventually be necessary
if a loose connection is identified, but indiscriminate intervention before
recording and investigating the symptoms can obscure the original fault.
Question 2
An artisan is
instructed to test the insulation resistance of an electrical installation
using an insulation resistance tester. Which procedure is most appropriate
before applying the test voltage?
A. Switch off the
installation's main switch but leave sensitive electronic equipment connected
to the circuit. B. Isolate the circuit, verify that it is de-energised, and
disconnect or protect equipment that could be damaged by the test voltage. C.
Leave the circuit energised and connect the tester across the conductors to
identify insulation deterioration. D. Disconnect the protective earth
conductor and use the tester between the phase conductor and the neutral
conductor while the circuit remains connected to its supply.
Answer: B.
Isolate the circuit, verify that it is de-energised, and disconnect or protect
equipment that could be damaged by the test voltage.
Rationale: Insulation resistance testing involves
applying a test voltage that can damage sensitive electronic devices,
surge-protection components, and other equipment that is not suitable for the
test. The circuit must therefore be isolated from its supply, and the absence
of voltage must be verified using an appropriate method before testing begins.
Equipment that could be affected by the test voltage must be disconnected or
protected in accordance with the manufacturer's instructions and the applicable
testing procedure. Switching off a main switch alone does not establish that
every conductor is safely isolated, particularly where alternative supplies or backfeeding
may exist. Applying an insulation resistance test to an energised circuit is
unsafe, while disconnecting the protective earth conductor does not make an
energised test acceptable. After testing, the circuit must also be discharged
as required before it is handled or returned to service.
Question 3
A technician
measures the voltage at the supply terminals of an electrical motor and obtains
the expected value. However, when the motor starts, its terminals show a
substantial voltage reduction and the motor struggles to accelerate. Which
explanation is most consistent with these observations?
A. The motor's
insulation resistance has necessarily increased, preventing the normal flow of
starting current. B. The supply frequency has necessarily increased, causing
the motor to demand less torque during acceleration. C. Excessive voltage drop
under starting load may result from supply impedance, undersized conductors, or
a high-resistance connection. D. The motor's protective earth conductor is
necessarily disconnected, preventing the supply voltage from reaching the motor
windings.
Answer: C.
Excessive voltage drop under starting load may result from supply impedance,
undersized conductors, or a high-resistance connection.
Rationale: A motor draws substantial current during
starting, and the impedance of the supply network and conductors produces a
voltage drop proportional to the current flowing through that impedance. If the
conductors are undersized, a terminal connection has excessive resistance, or
the supply impedance is unusually high, the voltage at the motor terminals may
fall significantly during acceleration. Reduced terminal voltage can impair
starting torque and prolong acceleration, potentially causing the motor to draw
elevated current for longer than expected. The normal voltage measured before
starting does not rule out these problems because the voltage drop may become
apparent only under load. Increased insulation resistance does not necessarily
explain the observed behaviour, increased supply frequency cannot be inferred
from the voltage readings, and a disconnected protective earth conductor does
not normally prevent the motor's phase-to-phase or phase-to-neutral supply
voltage from reaching its windings.
Question 4
During inspection
of a single-phase electrical installation, an artisan measures the expected
voltage between phase and neutral at a socket outlet. However, the connected
appliance operates intermittently, and the measured voltage changes when the
plug is moved slightly. Which fault should be investigated first?
A. An incorrectly rated circuit breaker that
trips when the appliance draws its normal operating current.
B. A defective appliance heating element
that causes excessive current whenever the appliance operates.
C. A loose connection in the fixed wiring
supplying the socket outlet.
D. A loose or damaged contact in the socket
outlet or plug connection that interrupts the supply intermittently.
Answer: D. A
loose or damaged contact in the socket outlet or plug connection that
interrupts the supply intermittently.
Rationale: An appliance that operates intermittently
when its plug is moved suggests a mechanical contact problem in the plug,
socket outlet, or associated termination. A loose or damaged contact can
interrupt current flow and may also produce local heating, arcing, and further
deterioration. The fact that the voltage changes when the plug moves is
particularly important because it connects the symptom to a physical
disturbance of the connection. The artisan should isolate the circuit safely,
inspect the relevant contacts and terminations, and carry out appropriate tests
before returning the installation to service. An incorrectly rated circuit
breaker would not ordinarily respond directly to movement of the plug, while an
appliance heating-element fault or a supply-frequency problem would not
normally explain a voltage change specifically associated with moving the plug.
The installation should not remain in service while the intermittent contact
fault is unresolved.
Question 5
A preventive
maintenance inspection reveals that a motor terminal connection has developed
discolouration and signs of overheating. The motor continues to operate, and
its measured current is within the expected range. What is the most appropriate
maintenance response?
A. Isolate the
equipment, inspect the affected connection and associated components, correct
the defect, and verify the connection before returning the motor to service. B.
Increase the motor's overload protection setting to prevent the terminal from
heating during normal operation. C. Continue operating the motor because a
normal current measurement establishes that the terminal connection is safe. D.
Replace the motor winding immediately because terminal discolouration confirms
that the winding insulation has failed.
Answer: A.
Isolate the equipment, inspect the affected connection and associated
components, correct the defect, and verify the connection before returning the
motor to service.
Rationale: Discolouration and overheating at a
terminal connection are warning signs of a potentially unsafe electrical
defect, even when the motor's measured current is within its expected range. A
loose termination, damaged contact surface, contamination, oxidation, or an
unsuitable connection can create localised resistance and heating without
producing an obvious overall overcurrent condition. The appropriate response is
to isolate the equipment, verify that it is safe to work on, investigate the
affected connection, and correct the identified defect using the manufacturer's
requirements and applicable procedures. The connection and surrounding
components should then be checked before the motor is returned to service.
Increasing the overload setting would not correct a high-resistance connection
and could compromise protection. Continued operation ignores a warning sign,
while terminal discolouration alone does not establish that the motor winding
has failed.
Question 6
An artisan uses a
digital multimeter to investigate a circuit that is suspected of containing a
broken conductor. The circuit is isolated and verified as de-energised. When
the meter is set to resistance, it displays an overload indication rather than
a numerical resistance value. What is the most appropriate interpretation?
A. The circuit
necessarily contains a short circuit because the meter cannot display the
resistance numerically. B. The resistance between the selected test points
exceeds the meter's measurable range or the circuit presents an open path. C.
The circuit necessarily has correct continuity because an overload indication
represents zero resistance. D. The circuit must be supplied with a higher
voltage before a resistance measurement can be completed.
Answer: B. The
resistance between the selected test points exceeds the meter's measurable
range or the circuit presents an open path.
Rationale: On many digital multimeters, an overload
indication in resistance mode means that the measured resistance exceeds the
selected range or that no conductive path is detected between the test points.
In an isolated circuit being investigated for a broken conductor, an open
circuit is therefore a plausible explanation. However, the indication alone
does not identify the exact physical location of the fault, and the artisan
should confirm that the leads are correctly connected, the meter is functioning
properly, and the selected test points are appropriate. A short circuit
normally produces a very low resistance reading rather than an overload
indication. An overload indication does not represent zero resistance, and
applying supply voltage to a circuit is not the correct way to complete an
ordinary resistance measurement. Further continuity checks at suitable points
can help locate the interruption.
Question 7
A technician
tests an isolated cable using an ohmmeter and finds that the resistance between
its two ends is substantially higher than expected. The cable length and
conductor size are known, and the test leads have been checked. Which condition
is the most plausible explanation?
A. The cable's
conductor has developed a lower resistance because its cross-sectional area has
increased. B. The cable's insulation resistance has necessarily fallen to zero
between the phase conductor and earth. C. Corrosion, conductor damage, or a
poor termination may have increased the resistance along the measured path. D.
The supply frequency has changed sufficiently to increase the cable's measured
DC resistance substantially.
Answer: C.
Corrosion, conductor damage, or a poor termination may have increased the
resistance along the measured path.
Rationale: The resistance of a conductor depends on
its material, length, cross-sectional area, and temperature. For a cable of
known length and conductor size, a resistance substantially above the expected
value may indicate damaged conductor strands, corrosion, an unsuitable joint,
or a poor termination within the measured path. Checking the test leads helps
reduce the possibility that the result is caused by the measuring arrangement,
although lead resistance and instrument limitations should still be considered
when measuring very low resistances. A low insulation resistance is a different
property measured between conductors or between a conductor and earth using an
appropriate insulation test. A reduction in conductor cross-sectional area
would generally increase resistance rather than decrease it. Supply frequency
does not ordinarily explain a substantial increase in the DC resistance
indicated by an ohmmeter.
Question 8
During
maintenance of an electrical installation, a circuit is found to have a
protective earth conductor that appears physically intact. Which test provides
the most direct evidence that the protective conductor forms an effective,
low-resistance path between the relevant protective connection points?
A. Measure the
phase-to-neutral supply voltage while the circuit is carrying its normal
operating load. B. Measure the insulation resistance between the phase
conductor and the neutral conductor. C. Measure the current consumed by the
connected appliance and compare it with its rated current. D. Perform a
protective-conductor continuity test using a suitable low-resistance test
instrument and appropriate test points.
Answer: D.
Perform a protective-conductor continuity test using a suitable low-resistance
test instrument and appropriate test points.
Rationale: A protective-conductor continuity test
directly assesses whether an electrically continuous path exists through the
protective conductor and its relevant connections. A conductor can appear
physically intact while a terminal is loose, a joint is corroded, or a
concealed section is damaged, so visual inspection alone cannot establish
effective electrical continuity. A suitable low-resistance test instrument and
appropriate test points help establish whether the measured resistance is
consistent with an effective protective path. Measuring phase-to-neutral
voltage assesses a different aspect of the circuit, while an insulation
resistance test between phase and neutral does not directly establish
protective-earth continuity. Measuring appliance current likewise provides no
direct proof that the protective conductor is continuous. The result should be
interpreted against the applicable installation requirements and the circuit's
design.
Question 9
A technician is
checking a single-phase resistive heater rated at 2,300 W and designed for a
230 V supply. Assuming the heater operates at its rated voltage and its
resistance remains approximately constant, what current should it draw during
normal operation?
A. 10 A,
calculated by dividing the rated power by the rated voltage. B. 0.1 A,
calculated by dividing the rated voltage by the rated power. C. 5 A,
calculated by dividing the rated power by twice the rated voltage. D. 20 A,
calculated by dividing twice the rated power by the rated voltage.
Answer: A. 10
A, calculated by dividing the rated power by the rated voltage.
Rationale: For a resistive heater operating at its
rated voltage, electrical power is given by \(P = VI\), where \(P\) is power in
watts, \(V\) is voltage in volts, and \(I\) is current in amperes. Rearranging
gives \(I = P/V\). Substituting the stated values produces \(I = 2,300/230 =
10\text{ A}\). The heater should therefore draw approximately 10 A under the
stated conditions. The other values result from incorrect arithmetic or
inappropriate manipulation of the power equation. This calculation is useful
when checking whether measured current is broadly consistent with an
appliance's rating, although actual readings may vary with supply voltage,
temperature, and the characteristics of the connected equipment.
Question 10
An artisan
measures a supply voltage of 230 V at a socket outlet while no appliance is
connected. After a 2,300 W resistive appliance is connected, the measured
voltage at the same outlet falls to 218 V. Assuming the appliance behaves
approximately as a constant-resistance load over this voltage range, which
conclusion is most appropriate?
A. The voltage
reduction proves that the supply frequency has fallen by approximately the same
percentage. B. The voltage reduction suggests that the supply path has
appreciable impedance and warrants investigation under load. C. The voltage
reduction proves that the appliance has developed an insulation fault to its
protective earth conductor. D. The voltage reduction establishes that the
circuit's protective device is incorrectly rated for the appliance.
Answer: B. The
voltage reduction suggests that the supply path has appreciable impedance and
warrants investigation under load.
Rationale: The reduction from 230 V to 218 V when
the appliance is connected indicates that the voltage at the socket is lower
under load than under no-load conditions. This can occur because current
flowing through the impedance of supply conductors, connections, or the
upstream network produces a voltage drop. The observation warrants further
investigation, particularly if the reduction exceeds the applicable
installation requirements or causes equipment to malfunction. The measurement
alone does not establish whether the cause is undersized conductors, a poor
connection, excessive upstream impedance, or another supply problem. It also
does not demonstrate a change in frequency, prove an insulation fault, or
establish that the protective device is incorrectly rated. Additional
measurements at appropriate points, carried out safely, can help determine
where the voltage drop originates.
Question 11
An artisan is
diagnosing a three-phase motor that hums when a start command is given but
fails to accelerate. The motor's supply and control arrangements require
further investigation. Which condition is an important possibility to check
before concluding that the motor itself is mechanically defective?
A. A
higher-than-normal insulation resistance that necessarily prevents the motor
from developing its rated rotational speed. B. A correctly balanced
three-phase supply that always prevents a motor from starting under mechanical
load. C. Loss of one supply phase or a fault in the starting circuit that
prevents normal motor acceleration. D. An increased protective-earth conductor
size that necessarily reduces the current available to the motor windings.
Answer: C.
Loss of one supply phase or a fault in the starting circuit that prevents
normal motor acceleration.
Rationale: A three-phase motor that hums but does
not accelerate may be experiencing single-phasing, a missing supply phase, a
defective contactor contact, an open circuit in the starting arrangement, or
another electrical fault that prevents the motor from receiving the intended
supply. Depending on the motor design and starting method, such conditions can
produce abnormal current, reduced torque, overheating, and failure to start.
The artisan should follow an appropriate diagnostic sequence, checking the
supply and control circuit safely before attributing the problem to mechanical
failure. A balanced supply ordinarily supports normal motor operation rather
than preventing it. High insulation resistance does not inherently prevent
acceleration, and increasing the protective-earth conductor size does not
ordinarily reduce the current available to the motor windings. The exact fault
must be established through suitable tests.
Question 12
A maintenance
team is preparing a preventive maintenance schedule for electrical equipment in
a facility. Which approach is most likely to reduce unexpected breakdowns while
making effective use of maintenance resources?
A. Inspect every
item of equipment at the same fixed interval, regardless of operating
conditions or failure history. B. Schedule maintenance only after equipment
has failed, using previous breakdowns to determine which parts require
replacement. C. Replace all electrical components annually, even when
inspection and operating records indicate that they remain serviceable. D. Set
maintenance intervals according to equipment criticality, manufacturer
guidance, operating conditions, observed deterioration, and failure history.
Answer: D. Set
maintenance intervals according to equipment criticality, manufacturer
guidance, operating conditions, observed deterioration, and failure history.
Rationale: An effective preventive maintenance
schedule considers the consequences of equipment failure, the manufacturer's
maintenance recommendations, the operating environment, the equipment's duty
cycle, and evidence from previous inspections and breakdowns. Equipment exposed
to dust, moisture, vibration, high temperatures, or frequent switching may
require different attention from equipment operating under less demanding
conditions. Critical equipment may also warrant more frequent inspection
because failure could interrupt an essential service or create a safety risk.
Applying the same interval to every item can waste resources on some equipment
while leaving other equipment inadequately maintained. Replacing components
automatically without evidence of need can introduce new defects and
unnecessary costs, while waiting for failure is primarily a reactive approach
rather than preventive maintenance. Maintenance records should be used to
improve future scheduling and identify recurring problems.
Question 13
A technician is
investigating a lighting circuit in which several lamps supplied by the same
circuit have become unusually dim. The lamps are compatible with the
installation, and the symptom began after maintenance work was performed on a
nearby junction box. Which investigation is most appropriate?
A. Check for a
loose or high-resistance connection and measure voltage at suitable points
under operating conditions. B. Replace all the lamps immediately because
simultaneous dimming confirms that every lamp has reached the end of its
service life. C. Increase the circuit breaker's rating because a higher rating
will restore the voltage available to the lamps. D. Disconnect the protective
earth conductor because it normally carries the current required to maintain
lamp brightness.
Answer: A.
Check for a loose or high-resistance connection and measure voltage at suitable
points under operating conditions.
Rationale: Several lamps becoming dim simultaneously
suggests that a shared part of the supply path may be affected. Because the
symptom began after nearby maintenance, a disturbed terminal, loose joint, or
other high-resistance connection should be considered. Measuring voltage at
appropriate points under operating conditions can help identify where the
abnormal voltage drop occurs. The investigation must be carried out using safe
isolation and testing procedures appropriate to each measurement. Simultaneous
dimming does not establish that all lamps have failed independently, and
increasing the circuit breaker's rating does not correct a poor connection or
restore the proper supply voltage. The protective earth conductor is intended
for protection against electric shock and fault conditions, not as a normal
return path for lamp operating current.
Question 14
A technician is
testing an isolated capacitor using a digital multimeter set to resistance
mode. After ensuring that the capacitor is safely discharged and disconnected
as necessary to prevent interference from parallel circuit paths, the
technician observes that the resistance reading initially changes before
becoming very high. Assuming the meter is connected in a configuration that
allows the capacitor to charge, which explanation best accounts for this
behaviour?
A. The capacitor
is necessarily short-circuited because its apparent resistance changes during
the measurement.
B. The meter initially charges the capacitor, causing the measured current to
decrease as the capacitor's voltage rises.
C. The circuit's supply frequency increases as the capacitor charges, causing
the resistance reading to rise.
D. The capacitor necessarily develops a permanent open circuit immediately
after the first meter reading.
Answer: B. The meter initially charges the
capacitor, causing the measured current to decrease as the capacitor's voltage
rises.
Rationale: When a resistance meter is connected
across a capacitor in a suitable circuit, the meter's internal source may cause
current to flow as the capacitor charges. As the capacitor voltage rises
towards the meter's applied voltage, the charging current decreases, and the
instrument may display a resistance that increases with time. A high final
reading can therefore be consistent with normal capacitor-charging behaviour,
depending on the circuit and instrument used. However, this observation alone
does not establish that the capacitor is in good condition; additional tests
may be required to assess capacitance, leakage, or other characteristics. A
changing resistance reading does not itself prove a short circuit, a permanent
open circuit, or a change in supply frequency. The capacitor must be safely
discharged before testing and handled according to the appropriate safety
procedures.
Question 15
An artisan is
instructed to investigate a circuit breaker that trips immediately when a
particular circuit is energised. The circuit has been isolated and made safe
for appropriate testing. Which finding would most strongly support the
possibility of a short circuit between current-carrying conductors?
A. An insulation
resistance reading between the relevant conductors that is very high and
stable. B. A protective-conductor continuity result that is consistent with
the expected low-resistance path. C. An abnormally low resistance between the
relevant isolated conductors after connected equipment and parallel paths have
been accounted for. D. A normal phase-to-neutral voltage measured at an
unrelated socket outlet on a separate circuit.
Answer: C. An
abnormally low resistance between the relevant isolated conductors after
connected equipment and parallel paths have been accounted for.
Rationale: A short circuit between current-carrying
conductors creates an unintended low-resistance path that can produce a large
fault current when the circuit is energised. With the circuit isolated,
suitable connected equipment and parallel paths accounted for, an abnormally
low resistance measurement between the relevant conductors can support the
diagnosis of a short circuit. The measurement must be interpreted carefully
because connected components may legitimately produce low resistance, and the
test arrangement can affect the result. A high insulation resistance between
conductors would generally indicate good insulation rather than a short
circuit. Protective-conductor continuity is a separate property, and a normal
voltage reading on an unrelated circuit does not establish the condition of the
circuit under investigation. The actual fault location should be confirmed
through systematic testing before repairs are completed.
Question 16
A single-phase
electrical installation uses a 230 V supply to operate a resistive load drawing
8 A. Assuming the load operates at the stated voltage and its power factor is
unity, what is its electrical power consumption?
A. 29 W, obtained
by dividing the supply voltage by the current. B. 1,150 W, obtained by
dividing the product of voltage and current by two. C. 1,840 kWh, obtained by
multiplying the voltage by the current and expressing the result as energy. D.
1,840 W, obtained by multiplying the supply voltage by the current.
Answer: D.
1,840 W, obtained by multiplying the supply voltage by the current.
Rationale: For a single-phase resistive load with a
power factor of unity, the electrical power is calculated using \(P = VI\).
Substituting the stated values gives \(P = 230 \times 8 = 1,840\text{ W}\),
equivalent to 1.84 kW. The result represents power, which is the rate at which
electrical energy is consumed, rather than energy itself. Energy would depend
on how long the load operates; for example, a 1.84 kW load operating
continuously for one hour consumes 1.84 kWh. Dividing voltage by current does
not calculate power, and halving the voltage-current product is not justified
by the stated conditions. Distinguishing between watts and kilowatt-hours is
important when interpreting equipment ratings, electricity consumption, and
maintenance measurements.
Question 17
During an
inspection, an artisan finds that a circuit's fuse has ruptured. Before
replacing it, the artisan needs to determine whether the fuse operated because
of a temporary abnormal condition or an unresolved fault. Which approach is
most appropriate?
A. Identify and
investigate the cause of operation, verify the circuit and load condition, and
fit a replacement fuse of the specified type and rating only when safe. B.
Install a fuse with twice the original current rating to prevent a repeat
interruption during the next operating cycle. C. Bridge the fuse terminals
temporarily with a conductor and observe whether the connected equipment
resumes normal operation. D. Replace the fuse with any available fuse of the
same physical size because physical compatibility establishes electrical
suitability.
Answer: A.
Identify and investigate the cause of operation, verify the circuit and load
condition, and fit a replacement fuse of the specified type and rating only
when safe.
Rationale: A ruptured fuse indicates that sufficient
current or another relevant operating condition caused the fuse element to
open. Before replacing it, the artisan should investigate possible causes such
as overload, short circuit, defective equipment, or an abnormal transient where
relevant. The circuit must be made safe, and appropriate checks should be
completed before restoring the supply. Any replacement must conform to the
specified current rating, breaking capacity, fuse characteristics, and circuit
design. Installing a higher-rated fuse without confirming the circuit's
requirements can allow conductors or equipment to overheat before the fuse
operates. Bridging the fuse removes an important protective function and
creates a serious hazard. Physical size alone does not establish that a fuse is
electrically suitable for the application.
Question 18
A technician is
asked to verify that a circuit breaker can interrupt an excessive current under
the conditions expected at the installation. Which specification is
particularly important when assessing whether the device can safely interrupt a
prospective short-circuit current?
A. The normal
operating voltage of the smallest appliance connected to the installation. B.
The circuit breaker's rated short-circuit breaking capacity relative to the
prospective fault current at its installation point. C. The resistance of the
protective earth conductor measured without considering the installation's
fault conditions. D. The number of switching operations performed by the
circuit breaker during its most recent maintenance period.
Answer: B. The
circuit breaker's rated short-circuit breaking capacity relative to the
prospective fault current at its installation point.
Rationale: A circuit breaker's rated short-circuit
breaking capacity indicates the level of short-circuit current it is designed
to interrupt safely under its specified operating conditions. The prospective
fault current at the installation point must not exceed the device's applicable
breaking capacity, and the protective device must also be suitable for the
circuit's voltage, system arrangement, and required protective characteristics.
A breaker with inadequate breaking capacity may fail to interrupt a severe fault
safely, even if its normal current rating appears appropriate. The smallest
appliance's operating voltage does not establish the fault-current level, and
protective-conductor resistance alone cannot establish the breaker's
interrupting capability. Switching history may inform maintenance decisions,
but it does not replace verification of the prospective fault current and the
device's rated breaking capacity.
Question 19
An artisan
measures the resistance of a copper conductor while it is cold and then repeats
the measurement after the conductor has become significantly warmer. Assuming
the conductor remains physically unchanged and the measurements are performed
correctly, what result is generally expected?
A. Its resistance
decreases because heating increases the number of available conduction paths in
copper. B. Its resistance remains exactly constant because conductor
temperature affects insulation but not metal resistance. C. Its resistance
increases because copper has a positive temperature coefficient of resistance
over ordinary operating temperatures. D. Its resistance becomes zero because
thermal expansion removes the electrical resistance between the conductor's
ends.
Answer: C. Its
resistance increases because copper has a positive temperature coefficient of
resistance over ordinary operating temperatures.
Rationale: Copper is a metal with a positive
temperature coefficient of resistance over ordinary electrical operating
temperatures. As its temperature rises, increased lattice vibrations impede the
movement of charge carriers, causing the conductor's resistance to increase.
For many practical calculations over a moderate temperature range, the
resistance change can be approximated using \(R_T = R_0[1+\alpha(T-T_0)]\),
where \(R_0\) is the resistance at the reference temperature, \(\alpha\) is the
temperature coefficient, and \(T-T_0\) is the temperature change. The exact increase
depends on the conductor's material and temperature range. Heating does not
ordinarily cause copper resistance to decrease or become zero. Temperature must
therefore be considered when interpreting precise resistance measurements and
assessing conductor performance under load.
Question 20
A technician is
checking an electrical motor control circuit. The contactor coil receives the
correct rated voltage when a start command is given, but the contactor does not
pull in. Which diagnostic direction is most appropriate after confirming that
the voltage measurement is valid?
A. Replace the
motor windings immediately because the motor must be preventing the contactor
coil from receiving voltage. B. Increase the supply voltage beyond the coil's
rating to overcome any mechanical resistance in the contactor. C. Disconnect
the protective earth conductor because the contactor cannot operate while its
protective connection remains intact. D. Investigate the contactor coil, its
mechanical movement, and any internal defect that could prevent operation
despite the correct applied voltage.
Answer: D.
Investigate the contactor coil, its mechanical movement, and any internal
defect that could prevent operation despite the correct applied voltage.
Rationale: If the contactor coil is receiving its
correct rated voltage but the contactor does not pull in, attention should turn
to the coil itself and the contactor's mechanical condition. Possible causes
include an open or damaged coil, a jammed armature, mechanical obstruction, or
internal damage that prevents the magnetic mechanism from operating. The
artisan should isolate the circuit before conducting resistance checks or
inspecting the mechanism, and should follow the manufacturer's maintenance
procedures. The motor windings are not the first suspect merely because the
contactor fails to operate, since the control device should be investigated
directly when the coil's supply has been verified. Applying a higher-than-rated
voltage can damage the coil, while disconnecting the protective earth conductor
does not correct the underlying fault and would compromise safety.
Question 21
During
maintenance of a distribution board, an artisan notices that a protective
device has operated, but the cause of the interruption is not immediately
apparent. The circuit supplies several items of equipment. Which approach is
most appropriate for distinguishing a faulty individual appliance from a fault
in the fixed wiring?
A. Isolate the
circuit, inspect the installation, and use a systematic process of testing the
wiring and assessing connected equipment separately. B. Replace the protective
device with a higher-rated model and restore all loads simultaneously to
identify which appliance operates first. C. Disconnect the protective earth
conductor and energise the circuit so that equipment faults become easier to
distinguish. D. Replace every connected appliance because operation of a
protective device confirms that all loads have developed electrical defects.
Answer: A.
Isolate the circuit, inspect the installation, and use a systematic process of
testing the wiring and assessing connected equipment separately.
Rationale: A protective device operating does not by
itself establish whether the cause lies in an individual appliance, the fixed
wiring, an overload condition, or another abnormal operating condition. A
systematic investigation begins by making the circuit safe, inspecting for
visible defects, and conducting appropriate tests on the wiring and connected
equipment. Depending on the protection involved and the initial findings,
equipment may need to be disconnected and assessed separately so that the
source of the fault can be identified without exposing personnel or equipment
to unnecessary risk. Replacing the protective device with a higher-rated model
can compromise protection and conceal the original problem. Disconnecting the
protective earth conductor is unsafe, while replacing all appliances without
evidence of individual faults is neither a sound diagnostic method nor an
efficient maintenance response.
Question 22
A technician
measures the voltage across a single-phase AC supply using a digital
multimeter. The displayed value is approximately 230 V. Which interpretation is
generally correct when the meter is configured for an appropriate AC voltage
measurement?
A. The reading
represents the maximum instantaneous voltage reached during each cycle of a
sinusoidal supply. B. The reading generally represents the RMS voltage, which
expresses the equivalent heating effect of the AC voltage in a resistive load. C.
The reading represents the arithmetic average of all instantaneous voltage
values over a complete symmetrical cycle. D. The reading represents the
peak-to-peak voltage, measured from the most negative to the most positive
point of the waveform.
Answer: B. The
reading generally represents the RMS voltage, which expresses the equivalent
heating effect of the AC voltage in a resistive load.
Rationale: Standard AC voltage measurements are
generally expressed as root-mean-square values, provided that the instrument is
configured appropriately and the waveform falls within its measurement
capabilities. The RMS value is particularly useful because it corresponds to
the DC voltage that would produce the same average heating effect in a
resistive load. For a pure sinusoidal waveform, an RMS voltage of approximately
230 V corresponds to a peak voltage of about \(230\sqrt{2}\), or 325 V, and a
peak-to-peak voltage of approximately 650 V. The RMS value is not the same as
the peak, peak-to-peak, or arithmetic average over a complete symmetrical
sinusoidal cycle. Actual readings depend on the waveform and the meter's
measurement method, so the instrument's specifications must be considered when
measuring distorted or non-sinusoidal voltages.
Question 23
A motor operates
normally for several minutes before its overload relay trips. The motor current
is subsequently found to be higher than its rated full-load current under the
observed operating conditions. Which interpretation is most appropriate?
A. The trip
necessarily proves that the overload relay has failed, regardless of the
motor's load and operating conditions. B. The trip proves that the protective
earth conductor has excessive resistance and must be replaced before any other
investigation. C. The motor may be experiencing sustained overload or another
condition causing excessive current, so the load and motor operating conditions
should be investigated. D. The trip establishes that the supply frequency is
exactly twice the motor's rated frequency during normal operation.
Answer: C. The
motor may be experiencing sustained overload or another condition causing
excessive current, so the load and motor operating conditions should be
investigated.
Rationale: An overload relay is designed to protect
a motor against sustained excessive current under the conditions for which the
protection has been selected and configured. A motor that runs for several
minutes before tripping, while drawing current above its rated full-load value,
may be experiencing excessive mechanical load, binding or friction, incorrect
operating conditions, or an electrical problem that increases current. The
artisan should investigate the driven equipment, compare actual operating conditions
with the motor's ratings, and verify the suitability and settings of the
protective arrangement. The trip alone does not prove that the relay has failed
or that the protective earth conductor is defective. It also provides no basis
for concluding that the supply frequency has doubled. A correct diagnosis
requires the operating conditions and measurements to be assessed together.
Question 24
A maintenance
team is investigating repeated failures of electrical connections in equipment
exposed to vibration. Inspection reveals that the connections become loose
after periods of operation, even though they were initially tightened. Which
maintenance improvement is most appropriate?
A. Apply the
highest possible tightening force to every terminal, regardless of the
manufacturer's specified torque. B. Increase the circuit current temporarily
so that the terminals heat up and establish more secure contact surfaces. C.
Eliminate all preventive inspections because initially correct tightening
proves that future loosening cannot be predicted. D. Investigate the effects
of vibration, verify terminal suitability and specified tightening
requirements, and implement appropriate measures to prevent recurrence.
Answer: D.
Investigate the effects of vibration, verify terminal suitability and specified
tightening requirements, and implement appropriate measures to prevent
recurrence.
Rationale: Repeated loosening of electrical
connections in equipment exposed to vibration indicates that the maintenance
response should address the underlying mechanical and electrical conditions
rather than simply repeat the same repair. The team should determine whether
the terminals and connectors are suitable for the application, whether
specified tightening torques have been followed, and whether the equipment
requires approved vibration-resistant connection methods or other
manufacturer-recommended measures. Excessive tightening can damage threads,
deform terminals, or compromise the connection, while deliberately increasing
current can create dangerous heating. Eliminating inspections would ignore a
recurring defect that may lead to high-resistance connections, arcing,
equipment failure, or fire. A preventive maintenance plan should incorporate
the findings and verify whether corrective measures successfully prevent
further loosening.
Question 25
An artisan is
testing an isolated single-phase circuit after a suspected insulation fault.
The insulation resistance between the phase conductor and protective earth is
found to be significantly lower than the expected value. Before returning the
circuit to service, which action is most appropriate?
A. Investigate
the low insulation resistance, identify and correct the underlying defect, and
repeat the required tests to verify that the circuit meets the applicable
acceptance criteria. B. Increase the circuit breaker's current rating because
doing so will restore the insulation resistance of the affected conductor. C.
Accept the circuit immediately if the phase-to-neutral voltage is correct,
because normal supply voltage establishes satisfactory insulation. D.
Disconnect the protective earth conductor permanently so that the insulation
resistance measurement no longer indicates a fault to earth.
Answer: A.
Investigate the low insulation resistance, identify and correct the underlying
defect, and repeat the required tests to verify that the circuit meets the
applicable acceptance criteria.
Rationale: A low insulation resistance between a
phase conductor and protective earth may indicate damaged insulation, moisture,
contamination, deteriorated cable material, a defective connected component, or
another unintended conductive path. The circuit should remain isolated while
the cause is investigated and corrected. The artisan should also confirm that
the test arrangement is appropriate and that connected equipment has been
treated in accordance with the applicable procedure. After repairs, the
required insulation resistance and other relevant verification tests should be
repeated to establish that the installation satisfies the applicable acceptance
criteria before it is returned to service. Increasing the circuit breaker's
rating does not repair insulation, and a normal phase-to-neutral voltage does
not establish satisfactory insulation resistance. Disconnecting the protective
earth conductor would compromise electrical safety rather than resolve the
defect.
Question 26
A single-phase
transformer has 1,000 turns on its primary winding and 200 turns on its
secondary winding. The primary winding is supplied with 230 V AC. Assuming an
ideal transformer, what secondary voltage should be expected?
A. 46 V, because
the secondary voltage is proportional to the primary-to-secondary turns ratio. B.
115 V, because the secondary winding has half the number of primary turns. C.
920 V, because the primary voltage is multiplied by the primary-to-secondary
turns ratio. D. 1,150 V, because the secondary voltage increases as the number
of turns decreases.
Answer: A. 46
V, because the secondary voltage is proportional to the primary-to-secondary
turns ratio.
Rationale: For an ideal transformer, the ratio of
primary voltage to secondary voltage equals the ratio of primary turns to
secondary turns: \(V_p/V_s=N_p/N_s\). Rearranging gives \(V_s=V_p(N_s/N_p)\).
Substituting the values gives \(V_s=230(200/1,000)=46\text{ V}\). The
transformer is therefore a step-down transformer because its secondary winding
has fewer turns than its primary winding. The other options result from
incorrect use of the turns ratio or an incorrect assumption about the
relationship between voltage and the number of turns. In a real transformer,
the measured secondary voltage may differ slightly because of winding
resistance, leakage reactance, and loading. The calculation assumes ideal
operation and an appropriate AC supply.
Question 27
A three-phase
motor is operating on a balanced supply. During maintenance, a technician
discovers that the motor rotates in the opposite direction to the direction
required by the driven equipment. Assuming the motor is suitable for reversal
and no manufacturer-specific restriction applies, which action will normally
reverse its direction of rotation?
A. Exchange the
protective earth conductor with the neutral conductor at the motor terminals. B.
Increase the overload relay setting until the motor develops sufficient torque
to rotate in the opposite direction. C. Interchange any two of the three phase
conductors using an approved isolation and reconnection procedure. D. Reverse
the polarity of the protective earth conductor while leaving all three phase
connections unchanged.
Answer: C.
Interchange any two of the three phase conductors using an approved isolation
and reconnection procedure.
Rationale: The direction of rotation of a
conventional three-phase induction motor depends on the phase sequence of its
supply. Interchanging any two phase conductors reverses that sequence and
normally reverses the motor's direction of rotation. The work must be performed
after appropriate isolation and verification that the circuit is safe, and the
technician should confirm that the driven equipment can safely operate in the
intended direction before restarting it. Protective earth and neutral
conductors must not be interchanged to reverse a motor, because they perform
different functions and such a change could create a serious safety hazard.
Increasing the overload relay setting does not reverse the phase sequence and
could compromise motor protection. The phase connections must be restored and
verified in accordance with the motor and installation requirements.
Question 28
A technician is
inspecting a distribution transformer that supplies a group of consumers. The
transformer has an unusually high operating temperature, although the ambient
temperature is within its normal range. Which investigation would provide the
most useful initial information about whether excessive loading is contributing
to the problem?
A. Measure the
resistance of the transformer enclosure and compare it with the resistance of
the neutral conductor. B. Measure the transformer load currents, compare them
with its ratings, and assess the loading and phase balance against its design
requirements. C. Disconnect the transformer protective earthing arrangement
and observe whether the enclosure temperature decreases. D. Increase the
secondary voltage above its specified value to determine whether the
transformer temperature stabilises.
Answer: B.
Measure the transformer load currents, compare them with its ratings, and
assess the loading and phase balance against its design requirements.
Rationale: Excessive loading can increase winding
losses and contribute to overheating in a distribution transformer. Measuring
the load currents and comparing them with the transformer ratings helps
establish whether the transformer is carrying more current than intended. In a
three-phase installation, the phase currents should also be assessed for
imbalance because uneven loading can contribute to unequal phase conditions and
additional losses. Other possible causes of overheating include inadequate
cooling, blocked ventilation, deteriorated insulation, internal defects, and
unsuitable operating conditions, so load measurements are an initial diagnostic
step rather than conclusive proof of the cause. Disconnecting protective
earthing would create a safety risk and would not correct overheating.
Increasing the secondary voltage beyond its specified value is not an
appropriate diagnostic procedure because it can damage connected equipment and
worsen operating conditions.
Question 29
An artisan is
examining an electrical installation in which metal enclosures of fixed
electrical equipment are connected to the protective earthing system. Which
statement best explains the primary safety purpose of this arrangement?
A. It ensures
that the normal operating current of every connected appliance returns through
the metal enclosure. B. It prevents all faults from occurring by maintaining
the voltage of every conductor at exactly zero volts. C. It increases the
normal operating voltage supplied to equipment whenever the circuit carries a
heavy load. D. It provides a protective path for fault current and helps
protective measures disconnect the supply when a dangerous fault occurs.
Answer: D. It
provides a protective path for fault current and helps protective measures
disconnect the supply when a dangerous fault occurs.
Rationale: Protective earthing connects exposed
conductive parts of electrical equipment to the installation's protective
earthing system so that, if a live conductor contacts a metal enclosure, a
fault-current path is established. Depending on the earthing arrangement and
protective devices, this path helps produce conditions that cause the supply to
be disconnected within the required time. Protective earthing does not prevent
every fault, does not guarantee that an enclosure will remain at exactly zero
volts under all conditions, and is not intended to carry normal load current in
an ordinary installation. It also does not increase the operating voltage of
connected equipment. Effective protection depends on the integrity of the
protective conductor, the earthing arrangement, the characteristics of the
fault, and the operation of the associated protective measures.
Question 30
A technician is
selecting a replacement cable for a circuit that carries a continuous load. The
proposed cable has the correct conductor material and nominal cross-sectional
area, but it will be installed in a hotter environment than the original cable.
Why must the installation conditions be considered before approving the
replacement?
A. Higher ambient
temperature can reduce the cable's permissible current-carrying capacity
because the conductor has less capacity to dissipate additional heat. B.
Higher ambient temperature necessarily increases the cable's permissible
current-carrying capacity because the conductor becomes more electrically
conductive. C. A cable with the same cross-sectional area always has the same
permissible current rating, regardless of installation method or surrounding
conditions. D. Ambient temperature affects insulation resistance only and has
no relevance to conductor temperature or current-carrying capacity.
Answer: A.
Higher ambient temperature can reduce the cable's permissible current-carrying
capacity because the conductor has less capacity to dissipate additional heat.
Rationale: A cable's permissible current-carrying
capacity depends on conductor size, insulation type, installation method,
ambient temperature, grouping with other cables, and other applicable
conditions. When the surrounding temperature increases, the cable has less
temperature margin available before its conductor or insulation reaches its
permitted operating limit. The allowable current may therefore need to be
reduced using the appropriate correction factors and installation requirements.
Selecting a cable solely on the basis of conductor material and cross-sectional
area can result in overheating if the actual installation conditions are more
demanding than those assumed in the original design. Higher temperature does
not automatically increase permissible current capacity, and the effects extend
beyond insulation resistance to include heat dissipation and the conductor's
operating temperature.
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