Electrical Fault Diagnosis and Rectification

what is the first step of safe isolation

• Identify the circuit

• Isolate the circuit

• Seek permission to Isolate

• Lock of the supply

A customer reports their main RCD is constantly tripping. The most likely fault would be;

• A Faulty appliance

• Rodent damage to cables

• To many appliances plugged in

• Human error during installation

the correct instrument to check a circuit is dead is:

• earth fault loop impedance tester

• low resistance ohms meter

• approved voltage indicator

• insulation resistance tester

To check the resistance of cable insulation you would use:

• An approved voltage indicator

• Multi-meter

• Insulation resistance tester

• Low resistance ohmmeter

A customer has nailed through a cable whilst pitting up a picture. the correct rectification would be.

• Renew the leg of cable completely and test the circuit

• Joint the cable where the nail has penetrated the cable, and test

• Remove the nail and hope for the best

• Leave the nail in the cable and plaster over it.

An existing 4 year old 3 phase motor has started to run slowly when on load, its extremely loud and the bearings are satisfactory. The possible fault could be

• One of the phase winding's have become open circuit

• Their is a short circuit between 2 phase windings

• The supply to the motor has been isolated

• The bearings are too tight

A MICC cable has been installed underground to feed a fish pond in a garden center. The cable has failed and is causing the fuse to blow. The possible fault could be

• too much load on the pond

• the outer sheath has became damaged and penetrated the inner cores

• too much voltage drop at the pond

• the cable has reached its lifespan and decided to give up

A fluorescent light fitting has failed to strike and is flickering, the possible faults could be:

• the supply voltage has dropped a little

• the starter could be faulty

• a short circuit fault is present on the supply circuit

• the tube could be faulty

An immersion heater is causing water to over heat, the possible fault causing this could be:

• the heater is drawing too much current

• the thermostat is stuck in the on position

• the heater is drawing too much voltage

• the thermostat is stuck in the off position

A 13 amps socket supplying a 3kw heater has burnt contacts; which is the correct statement below

• the socket should be taped up and changed at the next convenient opportunity.

• sockets shouldn't be used to supply 3kw heaters, this should be changed immediately to a 20amp double pole switch

• the socket isnt badly damaged therefore should be left alone until a major fault occurs.

• change the socket immediately.