WorksheetsUnit 114: Understand fault diagnosis and rectification
Total questions: 26
Worksheet time: 13mins
As an electrician, you are called out to a domestic dwelling. The consumer has purchased and attempted to fit a new ceiling fitting to replace an existing 3-plate ceiling rose. The consumer states that when the wall switch is turned on the circuit breaker trips. Assuming that the new fitting is not faulty, indicate what tests you would carry out to establish the cause of the fault.
Check for loose connections in the wiring.
Inspect the circuit breaker for damage.
Test the wall switch for faults.
Examine the ceiling fitting for incorrect wiring.
Identify the correct test instruments to be used for the following tasks.
Approved voltage indicator
Checking that circuit is dead
Low resistance ohmmeter
Continuity test on cpc
Low resistance ohmmeter
Ring final circuit test
Low resistance ohmmeter
Resistance check on element
Insulation resistance tester
Resistance check on cable insulation
When attempting to fix a mirror, a customer nails through a flat twin & cpc cable within the building fabric protected by embedded metal channelling. The 32A fuse protecting the circuit has blown. What should be done to rectify the situation?
Replace the fuse and leave the cable as is.
Remove the nail and repair the cable, then replace the fuse.
Remove the nail and patch up using insulation tape.
Only replace the fuse.
A three phase motor has been installed for a number of years. It is now found to be running slowly on load and making excessive noise. The bearings are satisfactory. What could be one possible fault?
Worn out bearings
Open circuit on one phase winding or line conductor
Overheating
Loose connections
An underground 4H10 MICV (pvc sheathed MI) cable has been installed directly in the ground at a pig farm. During a very wet period the cable fails and power supply is lost to the piggery. What could be the most likely possible cause of the fault?
Water ingress into the cable
Overloading of the cable
Physical damage by farm equipment
Natural aging of the cable
An underground 4H10 MICV (pvc sheathed MI) cable has been installed directly in the ground at a pig farm. During a very wet period the cable fails and power supply is lost to the piggery. How could the cause be confirmed?
By inspecting the cable for physical damage
By checking the moisture levels in the soil
By testing Insulation resistance between conductors.
By replacing the cable and observing if the issue persists
An underground 4H10 MICV (pvc sheathed MI) cable has been installed directly in the ground at a pig farm for a number of years. During a very wet period the cable fails and power supply is lost to the piggery. What is a means of providing a temporary supply to the piggery?
Temporary overhead supply
Install a new underground cable
Wait for the ground to dry
Use battery-powered lights
An underground 4H10 MICV (pvc sheathed MI) cable has been installed directly in the ground at a pig farm. During a very wet period the cable fails and power supply is lost to the piggery. State: d. A suitable alternative cable installation.
Use SWA cable
Install the cable above ground
Use a thicker cable
Replace with the same type of cable
State a possible reason for each of the following faults and suggest a solution: a. Switch start fluorescent fitting fails to start but just flickers.
The starter or tube is faulty; replace.
Open circuit, re-terminate.
Short circuit, repair cable.
The wiring is incorrect; check and correct the wiring.
Identify the possible reasons for each of the following faults and suggest a solution: b. Single phase capacitor start motor fails to start, it only vibrates. (3 answers)
The capacitor is faulty; replace the capacitor.
Open circuit on centrifugal switch; check operation.
Open circuit capacitor; check capacitor.
Reverse polarity of line conductors; re-terminate
Identify the likely reason for the following faults: An Immersion heater causes water to overheat.
Faulty thermostat
Broken heating element
Incorrect wiring
Low water level
Identify like reason(s) for a 13A socket supplying a 3kW heater having burnt contacts.
Overloading the socket with too much power
Using a socket with a lower current rating
Loose connection leading to overheating
All of the above
An operative carrying out fault diagnosis would not need to be familiar with:
supply earthing system
schedule of test results
repair cost
voltage present
Which of the following would not be required in a fault finding sequence:
time repair will take
safe isolation
testing
analysis of results
A continuity test as part of fault diagnosis would be carried out with which instrument:
earth-fault loop impedance tester
high resistance ohmmeter
low resistance ohmmeter
RCD tester
A loose termination could cause the following
short circuit between live conductors
overcurrent
arcing
operation of the protective device
Which of the following problems would not be classed as a transient fault
overload
lightning
heavy current switching
earth-fault voltages
The guidance for test leads used on instruments is contained in
BS 7671
EAWR
HASAWA
GS38
Which of the following documents is of least use when diagnosing faults?
Schedule of test results
Electrical Installation Certificate
Installation specification
Maintenance record
Which dead test would be carried out during initial fault diagnosis
RCD test
insulation resistance
functional
earth-fault loop impedance
On inspection of terminations at a motor, you observe conductor insulation has melted and discolouring of the terminal metal the most likely cause would be:
overcurrent
loose connection
open circuit
earth fault
Whilst fault finding you check and discover the BS 3036 fuse protecting the circuit has ruptured with globules of copper spattered over the holder together with black carbon powder. The most likely fault would be:
short circuit
open circuit
loose termination
broken conductor
Whilst fault finding, you check and discover the BS 3036 fuse protecting the circuit has melted in the middle only. The most likely fault would be:
open circuit
short circuit
loose termination
overload
A result of >100Ω on a continuity test would indicate what type of fault:
none
an insulation failure
open circuit
short circuit
An RCD would protect against the following fault:
open circuit
overcurrent
short circuit between live conductors
short circuit between live conductors and earth
Antistatic precautions would not usually be considered in the following installation type: a. office block b. chemical works c. petrol filling station d. flour mill.
office block
chemical works
petrol filling station
flour mill
