ELECTRICAL INSPECTOR EXAMINATION 18 November 2017 QUESTION AND ANSWER BOOKLET Time Allowed: Three hours

Transcription

1 Candidate Code No. IT 36 For Board Use Only Result Date Int Result Date Int ELECTRICAL INSPECTOR EXAMINATION 18 November 2017 QUESTION AND ANSWER BOOKLET Time Allowed: Three hours INSTRUCTIONS READ CAREFULLY You have 10 minutes to read this paper but do not start writing until you are told 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 pencils or red pens. Drawing instruments and pencils may be used when diagrams are required. Marks are allocated based on 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 of Practice. 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: The Electricity (Safety) Regulations 2010 reprint dated 4 April AS/NZS 3000:2007 (incorporating amendments 1 and 2) AS/NZS 3001:2008 (incorporating amendment 1) AS/NZS :2008 or AS/NZS : 2014 AS/NZS :2009 (incorporating amendment 1) PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM

2 Question 1 (a) WorkSafe must be notified if a danger to life is discovered while carrying out certain types of work. Refer to the Electricity (Safety) Regulations 2010 and state TWO types of work where this applies. (1) (2) Ref:.. (b) Refer to the Electricity (Safety) Regulations 2010 and state TWO conditions under which a homeowner can relocate existing switches, socket outlets and lighting outlets. (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

3 Question 1 continued (c) Refer to the Electricity (Safety) Regulations 2010 and state TWO earthing requirements for carrying out work on isolated high voltage fittings. (1) (2) Ref:.. (d) Refer to the Electricity (Safety) Regulations 2010 and state whether the inspection of work is considered prescribed electrical work. State a reference to support your answer. Ref:.. IT36 QUESTIONS 18 NOVEMBER

4 Question 1 continued (e) Refer to AS/NZS 3000 and state TWO requirements where a switch or circuit breaker is installed in a neutral conductor. (1) (2) Ref:.. (f) ELV final subcircuits have been installed in a secondary school science laboratory in accordance with AS/NZS Refer to AS/NZS 3000 and state TWO requirements for the ELV socket outlets installed on those ELV final subcircuits. (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

5 Question 1 continued (g) Refer to AS/NZS 3000 and state the TWO requirements relating to the resistance of protective earthing conductors in an electrical installation. (1) (2) Ref: (h) Refer to AS/NZS and state TWO items in a gas hazardous area for which up-to-date documentation shall be available for a periodic inspection. (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

6 Question 1 continued (i) Refer to AS/NZS and state: (i) The recommended interval between periodic inspections for moveable electrical equipment. (1 mark) Ref:.. (ii) The recommended interval between periodic inspections for enclosures which are frequently opened. (1 mark) Ref:.. (j) A motor control circuit incorporates a thermistor control relay and a thermal overload auxiliary contact. (i) What has occurred that would cause the thermistor control relay to open the control circuit. (1 mark) (ii) What has occurred that would cause the thermal overload auxiliary contact to open the control circuit. (1 mark) IT36 QUESTIONS 18 NOVEMBER

7 Question 2 (a) A new overhead service line has been installed to a 230V electrical installation. During the work, the phase and neutral were interchanged at the mains entry box. State TWO hazardous situations that could arise if the installation was livened. (4 marks) (1) (2) IT36 QUESTIONS 18 NOVEMBER

8 Question 2 continued (b) New mains have been installed in a 230V, single-phase domestic installation. The installation has been livened. Describe how you will carry out the testing required to determine whether or not a phase and neutral transposition has occurred. Include in your description: 1. The equipment used. 2. How the testing is carried out 3. The test results if there is no transposition 4. The test results if there is a transposition (6 marks) IT36 QUESTIONS 18 NOVEMBER

9 Question 3 Use AS/NZS 3000 to answer parts 3(a), 3(b), 3(c) and 3(d) (a) State TWO methods of determining the load current rating of an RCD installed on a switchboard in an electrical installation. (1) (2) Ref:. (b) Alterations and additions are being carried out in a domestic electrical installation. State THREE circumstances where RCD protection is not required to be installed. (3 marks) (1) (2) (3) Ref: IT36 QUESTIONS 18 NOVEMBER

10 Question 3 continued (c) RCBOs are to be installed on a switchboard in a new domestic electrical installation to protect the following circuits: Seven 2.5 mm 2 twin and earth TPS socket outlet final subcircuits. Two 1.5 mm 2 twin and earth TPS lighting final subcircuits. (i) State the current rating of an RCBO protecting a 2.5 mm 2 twin and earth TPS socket outlet final subcircuit. (½ mark) (ii) State the minimum number of RCBOs that must be installed to protect the 2.5 mm 2 twin and earth TPS socket outlet final subcircuits. (½ mark) Ref:. (iii) State the current rating of an RCBO protecting a 1.5 mm 2 twin and earth TPS lighting final subcircuits. (½ mark) (iv) State the minimum number of RCBOs that must be installed to protect the 1.5 mm 2 twin and earth TPS lighting final subcircuits. (½ mark) Ref:. IT36 QUESTIONS 18 NOVEMBER

11 Question 3 continued (d) RCCBs are to be installed on a switchboard in a new domestic electrical installation to protect the following MCBs. Eight 20A MCBs protecting twelve 2.5 mm 2 twin and earth TPS socket outlet final subcircuits. Three 10A MCBs protecting four 1.5 mm 2 twin and earth TPS lighting final subcircuits. (i) State the minimum number of RCCBs that must be installed on the switchboard? (1 mark) Ref:. (ii) State how the eight 20A MCBs and three 10A MCBs are distributed across the RCCBs stated in (d)(i) Ref:. IT36 QUESTIONS 18 NOVEMBER

12 Question 4 Introduction A single-phase, 230V electrical installation has the following resistive and inductive loads. Load 1 Resistive load 7500 W Load 2 Inductive load 4460 W I 25A pf 0.85 Load 3 Inductive load 3650 W I 16.87A pf 0.92 Use the information in the introduction to this question to answer parts 4(a), 4(b) and 4(c). (a) Calculate the kva of the installation. (4½ marks) IT36 QUESTIONS 18 NOVEMBER

13 Question 4 continued (b) Calculate the kvar of the installation. (4½ marks) (c) Which of the following transformers would be best suited for supplying the installation. (1 mark) 15 kva 20 kva 30 kva IT36 QUESTIONS 18 NOVEMBER

14 Question 5 The graph below shows typical characteristic curves for various HRC fuses. Use the information in the graph to answer parts 5(a), 5(b) and 5(c). IT36 QUESTIONS 18 NOVEMBER

15 Question 5 continued (a) A 230V, single-phase socket outlet final subcircuit is protected by a 32 A HRC fuse with a fusing factor (utilisation category) of 1.5. (i) Calculate the fusing current of the 32A HRC fuse. (1 mark) (ii) Refer to the graph in the introduction and determine how long it would take for the 32A HRC fuse to operate with the fusing current calculated in (a)(i) flowing. (1 mark) (iii) Refer to the graph in the introduction and determine the minimum fault current that needs to flow that will ensure the 32A HRC fuse will operate within the time stated in AS/NZS 3000 (1 mark) (iv) Calculate the impedance of the earth-fault loop that ensures the 32A HRC fuse operates within the time stated in AS/NZS 3000 IT36 QUESTIONS 18 NOVEMBER

16 Question 5 continued (b) A three-phase, 400V distribution switchboard is protected by a 32A HRC fuse on each phase. A 230V final subcircuit connected to that distribution switchboard is protected by a 16A HRC fuse. A 200A fault has occurred on the 230V final subcircuit. The 16A HRC fuse operated, the 32A fuse did not operate. Use the graph in the introduction to explain why the correct discrimination occurred. (3 marks) (c) Refer to AS/NZS 3000 and state TWO reasons why the impedance of the earth-fault loop of the final subcircuit needs to be as low as possible. (1) (2) Ref:. IT36 QUESTIONS 18 NOVEMBER

17 Question 6 Introduction A certified design has been prepared in accordance with Part 1 of AS/NZS 3000 for a 400V, three-phase MEN electrical installation. (A Part 1 installation ) All the equipment in the electrical installation operates at standard low voltage. Use the information in the introduction to this question and the Electricity (Safety) Regulations 2010 to answer parts 6(a), 6(b), 6(c) and 6(d). (a) State the THREE general items that must be contained in the certified design. (3 marks) (1) (2) (3) Ref:.. IT36 QUESTIONS 18 NOVEMBER

18 Question 6 continued (b) State the TWO safety outcomes that the certified design must achieve. (1) (2) Ref:.. (c) State TWO specific safety rules for the Part 1 electrical installation. (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

19 Question 6 continued (d) (i) State the document that details the inspection requirements for the Part 1 electrical installation. (1 mark) Ref:.. (ii) State TWO technical or safety statements that must be recorded in the written record of inspection for the Part 1 electrical installation. (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

20 Question 7 (a) In a 230V, single-phase electrical installation, the main neutral conductor between the distribution system and the main neutral bar has become open-circuited, while the installation is live. (i) Where in the installation will a voltage rise appear? (1 mark) (ii) What would occur if a person in the installation contacted the conductive parts of a Class I electrical appliance, even though the appliance is switched off. (iii) State what would occur if a fault of negligible impedance occurs on a final subcircuit in the installation. (3 marks) IT36 QUESTIONS 18 NOVEMBER

21 Question 7 continued (b) An earth-fault loop impedance test of 1.13Ω has been recorded on a final subcircuit supplying 230V, 15A socket outlets. The final subcircuit is protected by a Type C MCB. (i) Refer to AS/NZS 3000 and state the maximum rating of the MCB if a disconnection time of 0.4s under fault conditions is to be achieved. (1 mark) Ref:.. (ii) Refer to AS/NZS 3000 and state the minimum size cable that can be used to supply the 15A socket outlets. (½ mark) Ref:.. (iii) Refer to AS/NZS 3000 and state the maximum final subcircuit route length that can be installed to supply the 15A socket outlets. (½ mark) Ref:.. (c) An earth loop impedance tester shows a prospective short circuit current of 187A when connected to a 230V final subcircuit. Refer to AS/NZS 3000 and determine the type and rating of an MCB that should be installed that would operate within 0.4s under fault conditions. IT36 QUESTIONS 18 NOVEMBER

22 Question 8 Use AS/NZS 3001 to answer parts 8(a), 8(b), 8(c) and 8(d). (a) A Warrant of Electrical Fitness inspection for a new caravan is being carried out. The caravan is supplied by means of a permanently connected supply lead (a non-detachable connection) to the caravan. (i) State where the supply lead must be connected. (1 mark) Ref:.. (ii) State the requirement for the supply lead when it is not in use. (1 mark) Ref:.. (iii) State the requirement relating to the rating of the overcurrent protection for the supply lead. (1 mark) Ref:.. IT36 QUESTIONS 18 NOVEMBER

23 Question 8 continued (b) Specific types of single-phase socket outlets must be used to provide an electricity supply to a caravan from a caravan park service pillar. (i) State the Standards to which approved type of socket outlets must comply. (1 mark) Ref:.. (ii) State ONE reason why the requirements stated in (b)(i) are made. (c) State TWO protection requirements for an RCD protecting a socket outlet supplying a transportable structure (connectable installation). (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

24 Question 8 continued (d) In a caravan park, multiple sites for low consumption transportable structures can be supplied from one socket outlet. State TWO types of fittings that cannot be supplied from one socket outlet supplying low consumption transportable structures. (1) (2) Ref:.. IT36 QUESTIONS 18 NOVEMBER

25 Question 9 Introduction A 230V, PVC insulated two-core and earth copper TPS cable is to be installed to supply a new 230V distribution switchboard in a workshop in a ski-field. The new 230V distribution switchboard is supplied from a three-phase, 400V MEN main switchboard. The installation conditions are: The cable route length between the main switchboard and distribution switchboard is 50 metres: * In the 1 st 10 metres, the cable will be partially surrounded by thermal insulation, in a wiring enclosure * In the remaining 40 metres, the cable will be buried direct. The distribution switchboard load is 15.5 kw The maximum allowable voltage drop is 2%. The ambient air temperature is 20 o C The ambient soil temperature is 10 o C The maximum conductor temperature is 75 o C. Use the information in the introduction to this question and the following tables to answer parts 9(a), 9(b), 9(c) and 9(d). (a) Calculate the load current at the distribution switchboard. IT36 QUESTIONS 18 NOVEMBER

26 Question 9 continued (b) Calculate the minimum conductor size of the cable that can supply the load of the distribution switchboard. (3 marks) IT36 QUESTIONS 18 NOVEMBER

27 Question 9 continued (c) Calculate the minimum conductor size of the cable that can satisfy the voltage drop requirements. (4½ marks) (d) State the minimum conductor size of the cable that will satisfy the load and voltage drop requirements. (½ mark) IT36 QUESTIONS 18 NOVEMBER

28 Question 9 continued The following are extracts from AS/NZS TABLE 10 CURRENT-CARRYING CAPACITIES CABLE TYPE: INSULATION TYPE MAXIMUM CONDUCTOR TEMPERATURE REFERENCE AMBIENT TEMPERATURE TWO-CORE SHEATHED Cable with or without earth core, armoured or unarmoured, including neutral screened cables THERMOPLASTIC 75 0 C 30 0 c IN AIR, 15 0 C IN GROUND Conduc Current carrying capacity A tor Unenclosed Enclosed size Spaced Touching Exposed to sun Wiring enclosure in air Cu Al Cu Al Cu Al Cu Al mm 2 Flexible Flexible Flexible Flexible Solid/stra nded Solid/stra nded Solid/stra nded Solid/stra nded IT36 QUESTIONS 18 NOVEMBER

29 Question 9 continued TABLE 10 CONTINUED CURRENT-CARRYING CAPACITIES CABLE TYPE: INSULATION TYPE MAXIMUM CONDUCTOR TEMPERATURE REFERENCE AMBIENT TEMPERATURE TWO-CORE SHEATHED Cable with or without earth core, armoured or unarmoured, including neutral screened cables THERMOPLASTIC 75 0 C 30 0 c IN AIR, 15 0 C IN GROUND Current carrying capacity A Thermal insulation Buried direct Underground wiring enclosure Conduct or Partially Partially Completely Completely size surrounded by surrounded by surrounded by surrounded by thermal thermal thermal thermal insulation, unenclosed insulation, in a wiring enclosure insulation, unenclosed insulation, in a wiring enclosure mm 2 Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Solid/stra nded Flexible IT36 QUESTIONS 18 NOVEMBER

30 Question 9 continued TABLE 13 CURRENT-CARRYING CAPACITIES CABLE TYPE: INSULATION TYPE MAXIMUM CONDUCTOR TEMPERATURE REFERENCE AMBIENT TEMPERATURE THREE-CORE AND FOUR-CORE Cable with or without earth core, armoured or unarmoured, including neutral screened cables THERMOPLASTIC 75 0 C 30 0 c IN AIR, 15 0 C IN GROUND Conduc Current carrying capacity A tor Unenclosed Enclosed size Spaced Touching Exposed to sun Wiring enclosure in air Cu Al Cu Al Cu Al Cu Al mm 2 Flexible Flexible Flexible Flexible Solid/stra nded Solid/stra nded Solid/stra nded Solid/stra nded IT36 QUESTIONS 18 NOVEMBER

31 Question 9 continued TABLE 13 CONTINUED CURRENT-CARRYING CAPACITIES CABLE TYPE: INSULATION TYPE MAXIMUM CONDUCTOR TEMPERATURE REFERENCE AMBIENT TEMPERATURE THREE-CORE AND FOUR-CORE Cable with or without earth core, armoured or unarmoured, including neutral screened cables THERMOPLASTIC 75 0 C 30 0 c IN AIR, 15 0 C IN GROUND Current carrying capacity A Thermal insulation Buried direct Underground wiring enclosure Conduct or Partially Partially Completely Completely size surrounded by surrounded by surrounded by surrounded by thermal thermal thermal thermal insulation, unenclosed insulation, in a wiring enclosure insulation, unenclosed insulation, in a wiring enclosure mm 2 Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Solid/stra nded Flexible IT36 QUESTIONS 18 NOVEMBER

32 Question 9 continued Table 27(1) VARIANCE: INSTALLATION CONDITIONS AIR AND CONCRETE SLAB AMBIENT TEMPERATURES CABLES IN AIR OR HEATED CONCRETE SLAB Rating Factor Conductor temperature Air and concrete slab ambient temperature 0 C Table 27(2) VARIANCE: INSTALLATION CONDITIONS SOIL AMBIENT TEMPERATURES CABLES BURIED DIRECT IN GROUND OR IN UNDERGROUND WIRING ENCLOSURES Rating Factor Conductor temperature Soil ambient temperature 0 C IT36 QUESTIONS 18 NOVEMBER

33 Question 9 continued Table 42 THREE-PHASE VOLTAGE DROP (V c ) at 50 Hz CABLE TYPE: MULTICORE WITH CIRCULAR COPPER CONDUCTORS Three-phase voltage drop (V c) at 50 Hz, mv/a.m Conductor Conductor temperature, 0 C size mm 2 Max. 0.8 p.f. Max. 0.8 p.f. Max. 0.8 p.f. Max. 0.8 p.f. Max. 0.8 p.f Note: To convert to single-phase values multiply the three-phase value by Table 45 THREE-PHASE VOLTAGE DROP (V c ) at 50 Hz CABLE TYPE: MULTICORE WITH CIRCULAR ALUMINIUM CONDUCTORS Three-phase voltage drop (V c) at 50 Hz, mv/a.m Conductor Conductor temperature, 0 C size mm 2 Max. 0.8 p.f. Max. 0.8 p.f. Max. 0.8 p.f. Max. 0.8 p.f. Max. 0.8 p.f Note: To convert to single-phase values multiply the three-phase value by IT36 QUESTIONS 18 NOVEMBER

34 For Candidate s Use In the box, write the number of EXTRA sheets you have used. Write NIL if you have not used any For Examiner s Use Only Questions Marks Answered TOTAL IT36 QUESTIONS 18 NOVEMBER