ELECTRONIC SECURITY THEORY/REGULATIONS EXAMINATION 19 November 2011

Transcription

1 Candidate Code No. ESAI 27 For Board Use Only Result Date Result Date Int ELECTRONIC SECURITY THEORY/REGULATIONS EXAMINATION 19 November 2011 QUESTION AND ANSWER BOOKLET Time Allowed: 3 Hours INSTRUCTIONS READ CAREFULLY You have 10 minutes to read this paper but do not start writing until instructed to do so by the supervisor. Write your Candidate Code Number in the box provided above. Your name must NOT appear anywhere in this paper. Answer all questions. The pass mark for this examination is 60 marks. Use a pen for written answers. Do not use a pencil or a red pen. Drawing instruments and pencils may be used when diagrams are required. Marks are allocated on the basis of correctness. Do not use correcting fluid or correcting tape. Non-programmable calculators may be used. It is recommended that the reference source for your answers be included in the space provided if a question can be answered from the Act, Regulations, Standard or Code. However, just stating a reference only will earn no marks. For calculation questions all workings, including formulae, must be shown to gain full marks. Show answers to TWO decimal places. Warning You could get 0 marks for any question, or part of a question, if you show anything hazardous or dangerous in your answer. You will need to use the following documents in this examination: The Electricity Act 1992 reprint dated 2008 and The Electricity Amendment Act 2006 or The Electricity Act 1992 reprint dated 1 April 2010 Electricity (Safety) Regulations 2010 AS/NZS 3000:2007 and Amendment No 1 AS/NZS 3760:2003 and Amendment No 1 or AS/NZS 3760:2010 Int PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM

2 SECTION 1 THEORY Question 1 (a) State TWO factors which affect the severity of electric shock upon the human body. (1) (2) (b) An ohmmeter gives a reading of 24 ohms when used to measure the resistance of a plug-in heater designed for use on 230V/240V a.c. supply. If the heater draws 10 amps when plugged into a 240 V supply: (i) Will the current increase or decrease when the heater is plugged into a 230 V supply? (ii) Will the power dissipated increase or decrease when the heater is plugged into a 230 V supply? (c) Briefly explain why an ohmmeter should not be used when carrying out an insulation resistance test on the internal wiring of a single-phase, security alarm control panel. (d) One end of a main earthing conductor in an MEN electrical installation is connected to an earth electrode. Where must the other end be connected to? ESAI27 QUESTIONS 19 NOVEMBER

3 Question 1 continued (e) Briefly describe how earthing the metal frame of a Class I electrical appliance prevents electric shock hazards under fault conditions. ESAI27 QUESTIONS 19 NOVEMBER

4 Question 2 (a) (i) State ONE reason for carrying out an earth fault loop impedance test on a single-phase socket outlet circuit. (ii) Describe how the earth fault loop impedance tester is connected. (b) (i) State the reason for carrying out an RCD test on a single-phase portable RCD. (ii) Describe how the RCD tester is connected. (c) Identify which of the tests in (a) and (b) above are carried out on live circuits. ESAI27 QUESTIONS 19 NOVEMBER

5 Question 2 continued (d) (i) Describe how the prove test prove method of testing for isolation is carried out (3 marks) (ii) State why is it important to use the prove test prove method before working on electrical equipment? ESAI27 QUESTIONS 19 NOVEMBER

6 Question 3 (a) (i) What is meant by the term inverse time-current characteristic in relation to protective devices? (ii) Draw a typical inverse time-current characteristic as it applies to fuses. (b) Under what circumstance must back-up protection (for example, HRC fuses) be installed in addition to normal circuit protection? turn over) ESAI27 QUESTIONS 19 NOVEMBER

7 Question 3 continued (c) Explain how discrimination applies to protective devices in an electrical installation. (d) The current rating of a fuse relates to the maximum current the circuit can carry safely. (i) What would be the effect if the fuse was under-rated for the circuit? (ii) What would be the effect if the fuse was over-rated for the circuit? (e) (i) Under what circuit conditions is the electro-magnetic mechanism of an MCB specifically designed to operate (trip)? (ii) Under what circuit conditions is the thermal mechanism of an MCB specifically designed to operate (trip)? ESAI27 QUESTIONS 19 NOVEMBER

8 Question 4 Introduction A 230v single-phase 20A circuit consists of a permanent connection unit protected by a MCB. The permanent connection unit supplies a security alarm panel. The MCB has tripped out. When the MCB was reset, it tripped again. You have been requested to locate the cause of the fault and, if possible make repairs. You have established that: The MCB was not overloaded. The MCB is not faulty and is correctly rated for the circuit it protects. Use the information in the introduction to this question to answer parts (a), (b) and (c). (a) Describe how you would ensure that the circuit is safely isolated. (4 marks) ESAI27 QUESTIONS 19 NOVEMBER

9 Question 4 continued (b) There are TWO possible types of fault. What tests would you make to establish the cause of each fault. (3 marks) Fault 1 Fault 2 (c) Describe the action you would take for each of the possible faults. (3 marks) Fault 1 Fault 2 ESAI27 QUESTIONS 19 NOVEMBER

10 Question 5 (a) Describe the operation of an RCD circuit when there is a phase to earth fault (4 marks) (b) What is the residual current rating of an RCD used for personal protection? (c) A person received a severe electric shock when touching a faulty electrical appliance on a circuit protected by an MCB. Explain why the shock the person received would be much less severe if the circuit was also protected by an RCD. ESAI27 QUESTIONS 19 NOVEMBER

11 Question 5 continued (d) If a Residual Current Circuit Breaker (RCCB) is installed in a single-phase circuit, why is it necessary to also have overcurrent protection? (e) Describe what happens when the electricity supply to a Portable Residual Current Device (PRCD) is switched off and then switched on. ESAI27 QUESTIONS 19 NOVEMBER

12 Question 6 SECTION 2 SAFETY AND LEGISLATION (a) Refer to the Electricity (Safety) Regulations 2010 and briefly state the essential requirements of the term electrically safe. Ref: (b) A registered electronic security alarm installer is carrying out prescribed electrical work on an electrical installation. The electronic security alarm installer discovers that part of an installation presents an immediate danger to life. Refer to the Electricity (Safety) Regulations 2010 and state who the alarm installer must advise of the danger? Ref: (c) Refer to AS/NZS 3000 and state the requirements for flexible cords used as fixed wiring. Ref: ESAI27 QUESTIONS 19 NOVEMBER

13 Question 6 continued (d) Refer to AS/NZS 3000 and list FOUR types of equipment or conductors that form part of an MEN earthing system. (1) (2) (3) (4) Ref:. (e) Refer to the Electricity (Safety) Regulations 2010 and state what is meant by each of the following terms. (i) Earthed Ref:. (ii) Mains Ref: ESAI27 QUESTIONS 19 NOVEMBER

14 Question 7 (a) A registered electronic security alarm installer who carries out prescribed electrical work must be licensed. Refer to the Electricity Act 1992 and state: (i) The name of the licence? Ref: (ii) To whom must application be made for the licence stated in (a)(i)? Ref: (b) On which date does the licence stated in (a)(i) expire? (c) Persons who are required to report electrical accidents to the Secretary include registered electronic security alarm installers. (i) Refer to the Electricity Act 1992 and state the TWO results of an accident that must be reported to the Secretary. (1) (2) Ref: ESAI27 QUESTIONS 19 NOVEMBER

15 Question 7 continued (ii) Refer to the Electricity Act 1992 and state the circumstances under which a person can interfere with the scene of an accident without first notifying the Secretary. Ref: (d) Refer to the Electricity (Safety) Regulations 2010 and state THREE details that must be included in a report of an accident to the Secretary. (3 marks) (1) (2) (3) Ref: ESAI27 QUESTIONS 19 NOVEMBER

16 Question 8 A 230V plug-in, Class I security alarm panel that has repaired and the flexible cord and plug replaced. (a) The security alarm panel must be tested in accordance with which Standard? (b) Refer to the Standard stated in (a) and complete the following table in relation to the 230V plug-in, Class I security alarm panel. (4 marks) Type of test Type of instrument required (i) Earthing continuity Test result that will permit panel to be returned to service (ii) Insulation resistance test Ref: ESAI27 QUESTIONS 19 NOVEMBER

17 Question 8 continued (c) Refer to the Standard stated in (a) and describe FIVE checks that need to be carried out on the 230V plug-in, Class I security alarm panel. (5 marks) (1) (2) (3) (4) (5) Ref: ESAI27 QUESTIONS 19 NOVEMBER

18 Question 9 Introduction You have installed a new socket outlet for a 230V, plug-in, Class I security alarm panel. The new 2 core TPS cable has been run between the new socket outlet and an existing socket outlet but has not been connected to the existing socket outlet. Refer to AS/NZS 3000 and answer the following: (a) State the main reason for carrying out an insulation resistance test of the electrical work. Ref:. (b) State the required voltage of the insulation resistance tester when testing a low voltage electrical installation. Ref:. (c) (i) State TWO reasons why it is necessary to ensure correct circuit connections. (1) (2) Ref:. ESAI27 QUESTIONS 19 NOVEMBER

19 Question 9 continued (ii) Which test instrument would you use to test for correct circuit connections? (d) State the TWO reasons for testing the continuity of the protective earthing conductor. (1) (2) Ref:. (e) List TWO other mandatory checks and/or tests that are required to be carried out on this electrical work. (1) (2) Ref:. ESAI27 QUESTIONS 19 NOVEMBER

20 Question 10 (a) New flexible cords are to be fitted to a Class I and a Class II single-phase plug-in security alarm panels. (7½ marks) (i) Complete the following for the Class I (earthed) security alarm panel: (A) What is the minimum number of conductors required in the flexible cord? (B) State ONE set of colours for the conductors. For each colour, state the polarity. Note: To gain marks you must state the colours and polarity accurately. (C) Refer to AS/NZS 3760 and state the test or tests required to be carried out using test instruments. (ii) Complete the following for the Class II (double insulated) security alarm panel (A) What is the minimum number of conductors required in the flexible cord? ESAI27 QUESTIONS 19 NOVEMBER

21 Question 10 continued (B) State ONE set of colours for the conductors. For each colour, state the polarity. Note: To gain marks you must state the colours and polarity accurately. (C) Refer to AS/NZS 3760 and state the test or tests required to be carried out using test instruments. (b) Explain why the voltage at the load end of a flexible cord extension set supplying current to an electrical appliance is less than that at the supply end of the cord? (1½ marks) (c) All flexible cords are given a current rating. What does the term current rating mean? ESAI27 QUESTIONS 19 NOVEMBER

22 For Candidate s Use For Examiner s Use Only Questions Answered 1 Marks In the box, write the number of EXTRA sheets you have used. Write NIL if you have not used any TOTAL ESAI27 QUESTIONS 19 NOVEMBER