EPC 54 - Diagnosis & Rectification of Circuits Faults

Question 1

What is the basic item of information which must be available before an electrical fault can be diagnosed and rectified?

Answer 1

What the circuit is meant to do (operation of the circuit).

Question 2

What is the first check which should be carried out if an electrical device or circuit does not function as intended?

Answer 2

Ensure that the electrical supply is available.

Question 3

What basic precaution must be taken if OV is measured at the terminals of a connected electrical device?

Answer 3

Test the tester on a known voltage source.

Question 4

What Clause in AS/NZS 3000 gives a checklist for the visual inspection of a completed installation?

Answer 4

AS/NZS 3000 Clause 8.2.2.

Question 5

What are the SIX mandatory tests which must be carried out on any low voltage installation?

Answer 5

1. Continuity of earthing system
2. Insulation resistance
3. Polarities
4. Correct circuit connections
5. Verification of earth fault-loop impedance
6. Operation of RCDs.

AS/NZS 3000 Clause 8.3.3. Typical Isolation Procedure

Question 6

Explain the sequence of a typical isolation procedure.

Answer 6

1 Report to the Supervisor.

2 Identify with the Supervisor where the Distribution Board, CB, isolating switch, motor and known live sources are. Advise Supervisor that power is to be disconnected.

3 Complete JSA and make area safe.

3 Turn the isolating switch OFF, lock it in the OFF position, and attach a Danger Tag. Write your name, EW number, date and time on the Danger Tag.

4 Identify the relevant CB on the sub Distribution Board.
Isolate the supply by switching the circuit breaker to the OFF position. Lock it in the OFF

5 position, and attach a Danger Tag. Write your name, EW number, date and time on the Danger Tag.

6 Check the test instrument (a multimeter on a.c. volts scale) to see that it is working properly on a known voltage source.

7 Test for OV at the motor terminals. Test between all actives, from all actives to neutral (if there is a neutral), and from all actives to earth.

8 Re-check the test instrument to confirm that it is working properly on a known voltage source.

9 Double check all conductors using a phase pencil or voltage stick (Optional).

10 Label, then disconnect and remove ALL cables from the motor terminals.

11 Insulate all disconnected cables with tape and leave them in a safe and tidy condition.

12 Remove the motor from its mounting. If the task is not completed in the same shift, then remove Danger Tags and attach Out of Service Tags at the CB and isolating switch. Also replace personal locks with company
locks.

14 Advise the supervisor that the work is completed.