ELECTRICAL INSPECTOR EXAMINATION 14 November 2015 QUESTION AND ANSWER BOOKLET Time Allowed: Three hours

Transcription

1 Candidate Code No. IT 32 For Board Use Only Result Date Int Result Date Int ELECTRICAL INSPECTOR EXAMINATION 14 November 2015 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 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 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 may need to use the following documents in this examination: Electricity Act 1992 reprint dated 1 January 2014 Electricity (Safety) Regulations 2010 reprint dated 1 February 2014 or the reprint dated 1 August 2014 AS/NZS 3000:2007 (incorporating amendments 1 and 2) AS/NZS :2008 or AS/NZS : 2014 PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM

2 Question 1 (a) The Electrical Workers Registration Board has granted a person the power of entry to enter an electrical installation (a premises ). Refer to the Electricity Act 1992 and state ONE purpose for which the power of entry was granted. Ref:.. (b) A written complaint against an electrician is received by the Registrar of the Electrical Workers Registration Board. The Secretary must appoint an investigator to investigate the complaint. Refer to the Electricity Act 1992 and state the TWO main functions of an investigator (1) (2) Ref:.. 2

3 Question 1 continued (c) Refer to the Electricity (Safety) Regulations 2010 and state the TWO types of low risk prescribed electrical work that are not required to be certified on a certificate of compliance. (1) (2) Ref:. (d) Refer to the Electricity (Safety) Regulations 2010 and state: (i) The level of offence committed by a registered electrical inspector who gives a written record of inspection that is false in a material respect. Ref:.. (ii) The maximum fine that can be imposed on the registered electrical inspector for the level of the offence stated in (d)(i). Ref:.. 3

4 Question 1 continued (e) (i) Refer to AS/NZS 3000 and state the minimum depth for a vertical type electrode. (ii) Refer to AS/NZS 3000 and state the installation requirements for a strip-type earth electrode. (f) The supply to a three-phase distribution switchboard incorporates conductors connected in parallel. Refer to AS/NZS 3000 and state the how the size of the earthing conductor is determined. 4

5 Question 1 continued (g) (i) Refer to AS/NZS 3000 and state TWO requirements relating to the supply to extra-low voltage luminaires installed in Zone 0 of a swimming pool. (1) (2) (ii) Refer to AS/NZS 3000 and state the type of overhead electric line that cannot be installed over Zones 0, 1 or 2 of a swimming pool. Ref:.. (h) Refer to AS/NZS 3000 and state ONE reason why all three-phase socket outlets in a new electrical installation are tested with a phase sequence indicator. Ref:.. 5

6 Question 1 continued (i) In a 230V, single-phase electrical installation the main neutral conductor and main earthing conductor carry similar load currents because the main neutral has a high resistance joint. State TWO problems that this situation could cause in the 230V, singlephase electrical installation. (1) (2) (j) Prescribed electrical work comprising new mains and a new main earthing system has been installed in an existing low voltage electrical installation. When the installation was re-livened earthed metal in the installation became live. State TWO reasons either of which would cause the earthed metal in the installation to become live. (1) (2) 6

7 Question 2 (a) In an electrical installation the earth loop impedance is being measured of a 2.5 mm 2 twin and earth TPS socket outlet final subcircuit that is not protected by an RCD. The installation is not live. The final subcircuit is protected by a 20A, Type C MCB. (i) Refer to AS/NZS 3000 and state the test instrument that is used to measure the earth fault-loop impedance of the socket outlet final subcircuit. Ref: (ii) Refer to AS/NZS 3000 and describe how the earth fault-loop impedance of the socket outlet final subcircuit is measured using the instrument stated in (a)(i). (3 marks) Ref: 7

8 Question 2 continued (iii) Refer to AS/NZS 3000 and state the minimum or maximum resistance value of the impedance of the earth loop of the socket outlet final subcircuit. Ref: (b) State TWO reasons why the power factor of an industrial electrical installation is not improved beyond (1) (2) (c) The main switchboard of a factory has a maximum demand of 860kW at a power factor of 0.86 lag. The switchboard is supplied from a 1200kVA, 11,000/400V three-phase transformer with a 4% impedance. Calculate the VA of the maximum demand 8

9 Question 2 continued (d) Protective devices for certain circuits are required to operate within 0.4 seconds under fault conditions. (i) Refer to AS/NZS 3000 and state the supply voltage of a circuit where the protective device is required to operate within 0.4 seconds. (½ mark) (ii) Refer to AS/NZS 3000 and state ONE type of circuit where the protective device is not required to operate within 0.4 seconds. (½ mark) 9

10 Question 3 (a) You have been asked to provide advice on the electrical installation of a proposed new marina. (i) Refer to AS/NZS and state TWO types of electrical wiring systems that can be installed in a marina. (1) (2) (ii) Refer to AS/NZS and state TWO requirements relating to the number of sockets outlets in a low voltage marina service pillar. (1) (2). 10

11 Question 3 continued (iii) Refer to AS/NZS and state TWO methods of additional protection against electric shock (or protection against earth leakage current) on service pillars in a marina. (1) (2) (b) You are carrying out a periodic verification of an existing low voltage marina. (i) Refer to AS/NZS and state TWO inspection or testing requirements for RCDs protecting service pillar socket outlets. (1) (2) 11

12 Question 3 continued (ii) Refer to AS/NZS and state what is being verified when testing the fault rating of a protective device. 12

13 Question 4 (a) (i) Define the term pre-arc time as it applies to HRC fuses. (ii) Define the term total clearing time as it applies to HRC fuses. 13

14 Question 4 continued (b) A three-phase distribution board in an industrial electrical installation is protected by 50A HRC fuses. A 230V final subcircuit supplied by that distribution board is protected by a 20A HRC fuse. The following is an inverse time/current characteristic graph for the 50A HRC fuse and the 20A HRC fuse. The two curves on the left are those for the 20A fuse. The two curves on the right are for the 50A fuse. Refer to the graph and, using the terms pre-arc time and total clearing time, explain how correct discrimination is achieved between the 20A HRC fuse and the 50A HRC fuse when a fault current of 150A flows in the final subcircuit protected by the 20A HRC fuse. (4 marks) 14

15 Question 4 continued (c) Refer to AS/NZS 3000 and state the types of material that are not considered appropriate insulation for use in Class II equipment. (d) Clause 2.6 of AS/NZS 3000 details some situations where additional protection by the use of RCDs is required. Refer to AS/NZS 3000 and state TWO other situations where additional protection by the use of RCDs shall be installed. (1) (2) 15

16 Question 5 The 400V, three-phase electrical installation in an industrial building is completely new and has been designed and installed in accordance with Part 1 of AS/NZS (a) Refer to the Electricity (Safety) Regulations 2010 and state what outcome the person who designed the electrical installation must ensure. Ref:. (b) Refer to the Electricity (Safety) Regulations 2010 and state what outcome the person who installs the electrical installation must ensure. Ref:. (c) Refer to the Electricity (Safety) Regulations 2010 and state why the entire electrical installation is high risk prescribed electrical work and must be inspected. Ref:. 16

17 Question 5 continued (d) Refer to the Electricity (Safety) Regulations 2010 and state what the record of inspection of the high risk prescribed electrical work must contain in relation to the certified design. Ref:. (e) Refer to the Electricity (Safety) Regulations 2010 and state the TWO actions the person who inspected the high risk prescribed electrical work must do within 20 days of completing the written record of inspection. (1) (2) 17

18 Question 5 continued (f) AS/NZS 3000 details the various means of compliance with that Standard. Refer to AS/NZS 3000 and state THREE items that must be included in the documentation for a certified design. (3 marks) (1) (2) (3) 18

19 Question 6 Calculations have to be carried out to determine the heaviest loaded phase in a new 400 V, three-phase, FACTORY Assume a unity power factor. The installation has the following loads: Single-phase Number Equipment 12 38W Fluorescent 0.3A each 30 75W Fluorescent 0.8A each 7 150W outside floodlights 18 10A socket outlets (no permanently installed heating or cooking equipment is connected) 9 15A Socket outlets 1 5kW water heater (not instantaneous) 2 4kw Instantaneous water heaters Three-phase Number Equipment 2 9kW motors (15.8A per phase nameplate rating) 2 5kW motors (7.25A per phase nameplate rating) The objective is to balance the loads in AMPS over the three phases as evenly as possible. Use the tables of the following pages for the calculations. (10 marks) 19

20 Question 6 continued (a) Refer to AS/NZS 3000 and calculate the load of each of the single phase loads Equipment Load Group Calculation Load Amps 12, 38W Fluorescent lights 30, 75W Fluorescent lights 7, 150W outside floodlights 18, 10A socket outlets 9, 15A Socket outlets 1, 5kW water heater 2, 4kW Instantaneous water heaters 20

21 Question 6 continued (b) Balance the loads as evenly as possible across the three-phases to determine the heaviest loaded phase Equipment Load Group Calculation Load on each phase (amps) R W B 2, 9kW motors 2, 5kW motors 12, 38W Fluorescent lights 30, 75W Fluorescent lights 7, 150W outside floodlights 18, 10A socket outlets 9, 15A Socket outlets 1, 5kW water heater 2, 4kW Instantaneous water heaters Total Heaviest loaded phase = 21

22 Question 7 Introduction You have been engaged to carry out the periodic assessment of an existing domestic electrical installation which contains a number of RCDs for final subcircuit protection. You have a purpose made RCD tester for carrying out the RCD performance testing and it is fitted with a 3 pin plug for an electrically safe connection of the supply to the tester. Use the information in the introduction to this question to answer parts 7(a), 7(b), 7(c) and 7(d) (a) All RCDs used for personal protection are required to be of specific type. (i) Refer to AS/NZS 3000 and state the type of RCD permitted to be used in New Zealand. (ii) Refer to AS/NZS 3000 and draw the symbol for the type of RCD stated in (a)(i). 22

23 Question 7 continued (b) A 2-pole, 20A RCBO with a maximum residual current rating of 30 ma is being tested. Refer to the Electricity (Safety) Regulations 2010 and state the TWO permitted residual test currents and operating times for this RCBO. (4 marks) (i) (A) Residual test current (ma) (B) The maximum operating time (ii) (A) Residual test current (ma) (B) The maximum operating time (c) All RCDs used for final subcircuit protection are required to switch all live conductors (active and neutral). Explain why is this is a requirement. 23

24 Question 7 continued (d) In a single-phase 230V, domestic electrical installation there are three lighting final subcircuits and three socket outlet final subcircuits. (i) Refer to AS/NZS 3000 and state the minimum number of RCCBs required to be installed on the main switchboard for these final subcircuits. (ii) Refer to AS/NZS 3000 and explain why the requirement in (d)(i) is made? 24

25 Question 8 (a) You are to inspect a new industrial switchboard adjacent to a 500kVA, three-phase 400/230V distribution transformer. The network company has advised that the phase to phase no load voltage is 400V. The line voltage is 380V with 721A per phase flowing. You are to confirm the kva fault rating of the busbars and main ACB. Calculate (in any order): The required short circuit fault VA rating of the busbars and switchgear on the new transformer. The prospective short circuit current. (7 marks) 25

26 Question 8 continued (b) Define the term power factor. (c) Refer to AS/NZS 3000 and state the requirement for carrying out work on an electrical installation that is protected by auto-reclose type protective devices. 26

27 Question 9 Introduction A house has been relocated onto a rural lifestyle block and will be supplied by a dedicated 50kVA, three-phase, 11kV/400V transformer sited adjacent to the boundary fence. It is proposed to install a 400V, three-phase underground mains cable between the transformer and the house site. The installation conditions are: The cable route length is 125 metres, buried direct. The volt-drop is not to exceed 2.5% of the supply voltage between the installation point of supply and the house site. The transformer is 80% loaded. The ambient soil temperature is 15 O. The conductor temperature is 75 O. Use the information in the introduction to this question and information from the tables below to answer parts 9(a), 9(b) and 9(c). (a) Determine minimum size copper cable that will meet the load current requirements. (4½ marks) 27

28 Question 9 continued (b) Determine the minimum size copper cable that will meet the voltage drop requirements. (4½ marks) (c) State minimum size copper cable that will meet the load and volt drop requirements. 28

29 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

30 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

31 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

32 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

33 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

34 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

35 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 35