Unit 114: Understand fault diagnosis and rectification

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.

• Resistance check on element

• Low resistance ohmmeter

• Resistance check on cable insulation

• Low resistance ohmmeter

• Ring final circuit test

• Low resistance ohmmeter

• Checking that circuit is dead

• Insulation resistance tester

• Continuity test on cpc

• Approved voltage indicator

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