ELECTRICAL APPLIANCE SERVICEPERSON EXAMINATION 7 May 2016 QUESTION AND ANSWER BOOKLET

Transcription

1 Candidate Code No. EAS 1078 For Board Use Only Result Date Int Result Date Int ELECTRICAL APPLIANCE SERVICEPERSON EXAMINATION 7 May 2016 QUESTION AND ANSWER BOOKLET Time Allowed: 2 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. 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. You will need to use the following documents in this examination: Electricity (Safety) Regulations 2010 and Amendment No 1 AS/NZS 3000:2007 and Amendment No 1 and A AS/NZS 3760: 2010 PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM

2 Question 1 Each part in this question is worth 2 marks. Write your answer for each part in the box provided (a) When fighting a fire in live electrical equipment, which of the following fire extinguishers should not be used? 1. Vaporising liquid 2. Dry powder 3. Water - gas expelled 4. Carbon dioxide (b) The term Class II is found on the nameplate of many electrical appliances. This symbol is used to indicate: 1. A double insulated electrical appliance 2. A New Zealand Standard approved electrical appliance 3. An extra-low voltage electrical appliance 4. An electrical appliance to be supplied from an isolating transformer (c) A multimeter is connected in series with a 230V heating element to measure the current flow. The range switch on the meter has been left on the voltage setting. When the circuit is switched on, the meter will: 1. Burn out 2. Reduce the expected current flow through the element and indicate 230V 3. Cause the circuit fuse to blow 4. Indicate zero volts EAS 1078 QUESTIONS 7 MAY

3 Question 1 continued (d) A portable isolating transformer designed for personal protection is required to be tested after a new flexible cord has been fitted. What is the minimum insulation resistance test value which would be acceptable for the transformer when measured between the supply conductors and its metal case? 1. 1 Ω Ω MΩ 4. 1 MΩ (e) Which of the following wiring changes would reverse the direction of rotation of a single-phase universal motor? 1. Reverse the phase and neutral supply conductor connections at the motor terminal block. 2. Reverse the connections of the field windings 3. The direction of rotation cannot be changed on this type of motor. 4. Reverse the connections of the field windings and the armature windings (f) Under which of the following circuit conditions is a HRC fuse specifically designed to operate (blow)? 1. A short circuit 2. A small overload of short duration 3. A high motor starting current 4. An overload EAS 1078 QUESTIONS 7 MAY

4 Question 1 continued (g) The flexible cord of a 230V, Class II electrical appliance rated at 1 kw is to be replaced. The most suitable type of flexible cord to use would be: 1. Twisted conductor three core unsheathed 2. Light duty two core tough plastic sheathed 3. Ordinary duty three core tough plastic sheathed 4. Two single core conductors, unsheathed (h) A switch controls two heating elements both of the same resistance. The settings that can be selected on the switch are high, medium and low. When the low position is selected on the switch, it will connect: 1. Two elements in parallel across the supply 2. One element in series with a suitable resistance 3. One element only across the supply 4. Two elements in series with the supply (i) A thermal protective device is incorporated in a 230V electrical appliance. The main purpose of the thermal protective device is to provide protection against: 1. A drop in the insulation resistance 2. An overload 3. A rise in the resistance of the protective earthing conductor. 4. Leakage of current to earth EAS 1078 QUESTIONS 7 MAY

5 Question 1 continued (j) To comply with AS/NZS 3760, the insulation resistance test of a repaired electrical appliance that incorporates MIMS elements must not be less than: Ω 2. 10,000 Ω MΩ 4. 1 MΩ EAS 1078 QUESTIONS 7 MAY

6 Question 2 (a) Refer to AS/NZS 3000 and state FOUR areas inside a domestic residence that are earthed situations. (1) (2) (3) (4) Ref:. (b) A Class I, 230V electrical appliance is used in damp conditions without an electrical safeguard. (i) Describe how the damp conditions could affect the operation of the appliance. (ii) Describe the danger that may exist for an operator who uses the appliance and a phase to frame fault occurs. EAS 1078 QUESTIONS 7 MAY

7 Question 2 continued (c) A 230V, Class I electrical appliance must have a protective earthing conductor that has a resistance of 1Ω or less. State the main reason why the protective earthing conductor resistance must be 1Ω or less. (d) You have completed repairing a 230V, Class I, plug-in electrical appliance and the protective earthing conductor test result was 15Ω. State the sequence of actions you would take to rectify the high resistance and to ensure the appliance is safe to be returned to service. (3 marks) EAS 1078 QUESTIONS 7 MAY

8 Question 3 Introduction A 240V/230V plug-in heater incorporating two elements each of the same resistances is controlled by a three-heat switch. A multi-meter shows that the resistance of the appliance is 26.45Ω when the three-heat switch is in the high position. AS/NZS 3000 states that the maximum voltage-drop on a socket outlet in an electrical installation cannot exceed 5%. Use the information in the introduction to this question to answer parts 3(a), 3(b), 3(c) and (d). (a) Calculate the power the heater will consume when operating at 230V and the three heat switch is in the medium position. (3 marks) (b) Calculate the current drawn by the heater when operating at 230V and the three heat switch is in the high position. EAS 1078 QUESTIONS 7 MAY

9 Question 3 continued (c) (i) Calculate the voltage at the socket outlet when the maximum voltage drop occurs. (ii) Calculate the power the heater will consume when the three-heat switch is in the high position and the maximum permitted voltage drop occurs at the socket outlet. (d) Will the power consumed by the heater increase or decrease when operating at 240V? EAS 1078 QUESTIONS 7 MAY

10 Question 4 (a) Some electrical appliances are being supplied from a 25 metre three core flexible extension cord. The extension cord is wound on a cable drum. The load of the appliances is 90% of the full-load rating of the extension cord (i) Describe how the extension cord might fail if it is continued to be used while wound on the cable drum (ii) Unwinding extension cord from the drum is one precaution that can be taken to prevent the cord failing. State ONE other precaution that could be taken to prevent the extension cord failing while still wound on the drum. (b) State what the term current rating means when it is applied to a flexible cord. EAS 1078 QUESTIONS 7 MAY

11 Question 4 continued (c) A 230V electrical appliance is being supplied from a socket outlet via a flexible extension cord. The appliance cannot develop its full power output because of voltage drop. State TWO methods of reducing the effect of voltage drop in the extension cord. (1) (2) (d) State ONE reason why three-pin plugs must not be connected to both ends of a flexible extension cord. (e) Can a two-core extension cord be used to supply a 230V, plug-in, Class I electrical appliance? State a reason to support your answer. EAS 1078 QUESTIONS 7 MAY

12 Question 5 (a) When replacing a HRC cartridge fuse which has blown, the replacement must have characteristics the same as the original. One of these characteristics is the voltage rating. State THREE other electrical characteristics to be checked for similarity. (3 marks) (1) (2) (3) (b) State TWO advantages that HRC fuses have when compared to rewireable fuses. (1) (2) (c) State TWO safety reasons why terminals of HRC fuse carriers must not be bridged with fuse wire of the same current rating as the blown cartridge. (1) (2) EAS 1078 QUESTIONS 7 MAY

13 Question 5 continued (d) A rewireable fuse is being reloaded. State TWO reasons why it is important to thread the fuse wire from terminal to terminal through the tortuous path in the fuse carrier. (1) (2) (e) State what the term current rating means when it is applied to a HRC fuse. EAS 1078 QUESTIONS 7 MAY

14 Question 6 (a) Tests were carried out on Class I, 230 V single-phase plug-in dish washer after a complaint of a homeowner receiving an electric shock. The test results were: Protective earthing conductor test 3.25Ω between the earth pin of the plug and appliance. the frame of the Insulation resistance test A 6Ω fault between the active conductor and the frame of the dishwater with the dishwasher switch in the off position (i) Calculate the current that would have flowed to earth when the dishwasher was plugged in and turned on. (2½ marks) (ii) The socket outlet was protected by a 20A HRC fuse with a 1.5 utilisation category (fusing factor). Determine by calculation whether or not the fuse would operate. EAS 1078 QUESTIONS 7 MAY

15 Question 6 continued (iii) Calculate the shock voltage that would have appeared on the frame of the dishwasher when it was plugged in and turned on. (2½ marks) (b) A 230V, Class I, plug-in electrical appliance is controlled by a single pole switch. You are testing the appliance with an ohmmeter and find that the neutral is switched. Describe TWO wiring errors that would result in the neutral being switched. (1) (2) (c) State ONE unsafe situation in an electrical appliance that a phase and neutral transposition could create. EAS 1078 QUESTIONS 7 MAY

16 Question 7 (a) A new fuse needs to be inserted into a fuse carrier to replace a blown fuse on a domestic switchboard. The circuit protected by the fuse supplies a 230V plug-in electrical appliance. Describe TWO safety reasons why it is recommended that the main switch should be turned off before removing the fuse carrier or replacing it into the fuse base. (1) (2) (b) A 230V plug-in electrical appliance has been withdrawn from service for repair. Describe ONE method of ensuring the continued isolation of the electrical appliance to prevent it being used before being repaired. EAS 1078 QUESTIONS 7 MAY

17 Question 7 continued (c) State the difference between switching off an electrical appliance and isolating an electrical appliance? (3 marks) (d) Refer to the Electricity (Safety) Regulations 2010 and state the TWO practical steps an employee must take when carrying out work requiring personal protective equipment. (4 marks) (1) (2) Ref:.. EAS 1078 QUESTIONS 7 MAY

18 Question 8 (a) After repairs have been carried out on a 230V, Class I plug-in heater, a visual inspection should be carried out in addition to the prescribed electrical tests. (i) Refer to AS/NZS 3760 and state THREE visual inspections relating specifically to the plug and flexible cord (but not the appliance) (3 marks) (1) (2) (3) Ref:. (ii) Refer to AS/NZS 3760 and state TWO visual inspections relating specifically to the appliance (but not the plug and flexible cord) (1) (2) Ref:. EAS 1078 QUESTIONS 7 MAY

19 Question 8 continued (b) A microgap switch, rated at 10A, 230V a.c. only, is used as the control switch on the Class I heater. State ONE reason why this switch would not be suitable for use on a d.c. circuit of similar current and voltage. (c) Explain why the earth pin of a standard New Zealand 3 pin 10A plug used to supply a 230V, Class I heater is longer than the phase or neutral pins. (d) State TWO reasons why a bayonet cap adaptor must not be used to supply a 230V, Class I, 2 kw plug-in heater. (1) (2) EAS 1078 QUESTIONS 7 MAY

20 Question 9 (a) You are required to carry out a protective earthing conductor test on a 230V, Class I plug-in electrical appliance. (i) State the instrument that should be used for this test. (ii) Explain how the test should be carried out. (iii) (1) What is the acceptable resistance for this test? (½ mark) (2) Is this resistance a minimum or maximum value? (½ mark) (b) Explain why an ohmmeter is not the correct instrument to carry out an insulation resistance test on a portable electrical appliance. EAS 1078 QUESTIONS 7 MAY

21 Question 9 continued (c) The 230V, Class I electrical appliance is connected to the electricity supply and is live. (i) What type of test would you carry out to test the integrity of the insulation? (ii) What type of test instrument should be used to carry out the test you have stated in (c)(i)? (iii) What are you measuring when you are carrying out the test you have stated in (c)(i) on the electrical appliance using the instrument you have stated in (c)(ii). (iv) What maximum test result would you expect if the appliance is to comply with AS/NZS 3760? EAS 1078 QUESTIONS 7 MAY

22 For Candidate s Use For Examiner s Use Only Questions Answered Marks In the box, write the number of EXTRA sheets you have used. Write NIL if you have not used any TOTAL MARKS EAS 1078 QUESTIONS 7 MAY