ELECTRICIANS REGULATIONS EXAMINATION 25 June 2011

Transcription

1 ER42 Candidate Code No. For Board Use Only Result Date Result Date Int ELECTRICIANS REGULATIONS EXAMINATION 25 June 2011 Int QUESTION AND ANSWER BOOKLET INSTRUCTIONS READ CAREFULLY Time Allowed: Three hours 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. 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 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. 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 may 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 3001:2008; AS/NZS :2008; AS/NZS 3760:2003 and Amendment No 1 or AS/NZS 3760: 2101; AS/NZS 3019: 2007 NZECP 34 PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM

2 Question 1 (a) Fittings are installed in an electrical installation. Refer to the Electricity (Safety) Regulations 2010 and state TWO situations where fittings that are installed in an installation are specifically deemed to be electrically unsafe. (1) (2) (b) Refer to the Electricity (Safety) Regulations 2010 and state TWO details of an electrical accident that must included in a report to the Secretary. (1) (2) 2

3 Question 1 continued (c) Automatic disconnection of supply is a permitted method of fault protection (protection against indirect contact) and overcurrent protection (to prevent injury or damage). Refer to AS/NZS 3000 and state ONE situation where an overload protective device may be omitted? (d) Refer to AS/NZS 3000 and state the TWO types of faults that RCDs do not provide protection against. (1) (2) (e) Refer to AS/NZS 3000 and state the requirements for installing a main switchboard near a swimming pool. 3

4 Question 1 continued (f) Refer to AS/NZS 3000 and state ONE requirement for installing a main switchboard near an automatic fire sprinkler. (g) A single-phase electrical installation operates at standard low voltage. Refer to AS/NZS 3000 and calculate the maximum permitted voltage drop between the point of supply and a socket outlet (h) Refer to AS/NZS 3000 and state: (i) The colours permitted to identify the active (phase) conductor of a single-phase final subcircuit? (ii) The colours permitted to identify equipotential bonding conductors? 4

5 Question 1 continued (i) A 4mm 2 two-core neutral-screened submain cable is to be buried direct (unenclosed) in the ground in an unpaved area run between two buildings. Refer to AS/NZS 3000 and state the TWO requirements for indicating the position of the buried cable. (1) (2) (j) Refer to AS/NZS 3000 and state TWO requirements for socket outlets in extra-low voltage electrical installations. (1) (2) 5

6 Question 2 A 400V/230V motor control centre is being installed in a factory. The control centre will provide individual circuits to a number of single-phase and three-phase motors. Motors are either permanently connected or supplied by a plug and socket arrangement. The smallest motor is rated at 100 VA. (a) One of the three-phase motors has the isolating switch installed in the motor supply circuit. Refer to AS/NZS 3000 and state TWO requirements relating to the rating of the isolating switch in the motor supply circuit. (1) (2) (b) One of the other three-phase motors has the isolating switch installed in the motor starter circuit. Refer to AS/NZS 3000 and state the requirement relating to the rating of the isolating switch in the motor starter circuit. 6

7 Question 2 continued (c) Refer to AS/NZS 3000 and state the TWO situations where a switch for the disconnection of supply for maintenance purposes is not required. (1) (2) (d) Refer to AS/NZS 3000 and state the TWO situations where overtemperature protection shall not be provided for a motor. (1) (2) (e) Some three-phase motors are controlled by star/delta starters. State the main reason why interlocks are used in a star/delta starter. 7

8 Question 3 A three-phase 400V oven is to be installed in a restaurant. The electrician has calculated in accordance with Part 2 of AS/NZS 3000, that the minimum size cable that will meet all requirements is a 4mm 2, 4 core, TPS copper cable. You have to confirm - or otherwise - using calculations that the 4 mm 2, 4 core TPS copper cable is the minimum size cable that meets the load and voltage drop requirements. (a) Calculate whether the 4mm 2, 4 core, TPS copper cable meets the load requirements by using the information below and relevant information from the tables on pages 10, 11 and 12. The cable route length is 20 metres in length. The load is 25 kw The cable is fixed directly (touching). The ambient air temperature is 20 0 C. The voltage at the switchboard is 400 V. The permitted voltage drop from the switchboard to the oven must not exceed 1.5% The conductor temperature is assumed to be 75 0 C (4½ marks) 8

9 Question 3 continued (b) Calculate whether the 4mm 2, 4 core, TPS copper cable meets the voltagedrop requirements by using the information below and relevant information from the tables on pages 10, 11 and 12. The cable route length is 20 metres in length. The load is 25 kw The cable is fixed directly (touching). The ambient air temperature is 20 0 C. The voltage at the switchboard is 400 V. The permitted voltage drop from the switchboard to the oven must not exceed 1.5% The conductor temperature is assumed to be 75 0 C (3½ marks) (c) Is the 4mm 2, 4 core, TPS copper cable the minimum size cable that meets the load and voltage drop requirements? State a reason to support your answer. 9

10 Question 3 continued The following are extracts from AS/NZS Table 9 Current Carrying Capacities of Two-Core O.6/1 kv Insulated and Sheathed (including Neutral Screened) Cables with or without Earth Conductor, Armoured or Non-Armoured Cables Current carrying capacity A Unenclosed Enclosed Buried Direct Con duct or size Spaced Touching Nonmetallic wiring enclosures in air round cable Nonmetallic wiring enclosures in air flat cable In nonmetallic wiring enclosures or unenclosed partially surrounded by thermal insulation Completely surrounded by thermal insulation Underground non-metallic wiring enclosure mm 2 Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Note: The ratings are based on 30 0 C ambient air temperature and 15 0 C ambient soil temperature 10

11 Question 3 continued Table 12 Current Carrying Capacities of Three-Core And Four-Core O.6/1 kv Insulated and Sheathed (including Neutral Screened) Cables with or without Earth Conductor, Armoured or Non-Armoured Cables Current carrying capacity A Unenclosed Enclosed Buried Direct Con duct or size Spaced Touching Nonmetallic wiring enclosures in air round cable Nonmetallic wiring enclosures in air flat cable In nonmetallic wiring enclosures or unenclosed partially surrounded by thermal insulation Completely surrounded by thermal insulation Underground non-metallic wiring enclosure mm 2 Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Cu Al Note: The ratings are based on 30 0 C ambient air temperature and 15 0 C ambient soil temperature Table 27(1) Rating Factors for Variations in Ambient Temperature for Cables in Air or Heated Concrete Slabs and for Cables Buried Direct in the Ground or in Underground Wiring Enclosures Air And Concrete Slab Temperatures Rating Factor Ambient temperature Conductor temperatur e 0 C

12 Question 3 continued Table 27(2) Rating Factors for Variations in Ambient Temperature for Cables in Air or Heated Concrete Slabs and for Cables Buried Direct in the Ground or in Underground Wiring Enclosures Soil Temperatures Rating Factor Ambient temperature Conductor temperatur e 0 C Table 42 Three-Phase Voltage Drop at 50Hz of Multicore Cables with Circular Copper Conductors Three-phase voltage drop at 50 Hz, mv/a.m Conducto Conductor temperature, 0 C r 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

13 Question 4 You are wiring a new low voltage electrical installation. The electrical installation has been designed in accordance with Part 1 of AS/NZS (a) Before wiring the installation you are required to hold a Declaration of Conformity for that installation. Refer to the Electricity (Safety) Regulations 2010 and answer the following: (i) State TWO aspects that must be included on the Declaration of Conformity. (1) (2) (ii) Which aspect of the Declaration of Conformity are you required to ensure while wiring the installation. 13

14 Question 4 continued (b) You are wiring a new house. The house has been designed in accordance with Part 2 of AS/NZS The Electricity (Safety) Regulations 2010 requires that electrical work on the low voltage electrical installations is tested in accordance with AS/NZS AS/NZS 3000 details the instrument tests that are required carried out. (i) Which instrument tests detailed in AS/NZS 3000 can only be carried out with the electrical installation live? (ii) Which instrument tests detailed in AS/NZS 3000 can be carried out with the electrical installation disconnected from the electricity supply or with the electrical installation live? (iii) Which instrument tests detailed in AS/NZS 3000 can only be carried out with the installation disconnected from the electricity supply? 14

15 Question 4 continued (iv) You have completed wiring the electrical installation. Refer to the Electrical (Safety) Regulations 2010 and state which part of the work is required to be inspected by a registered electrical inspector. (v) After wiring the electrical installation you have to complete a Certificate of Compliance. The work can be certified if you are satisfied that two situations exist. Refer to the Electricity (Safety) Regulations 2010 and state those TWO situations. (1) (2) 15

16 Question 5 Earthing arrangements are an integral part of the New Zealand MEN system. (a) The three phase copper mains to an industrial installation has active conductor sizes of 25mm 2, 25mm 2 and 35mm 2. Refer to AS/NZS 3000 and answer the following: (i) Explain how the minimum size of the main earthing conductor for this installation is determined? Include a reference source to support your answer. (ii) State the minimum size the main earthing conductor for this installation. Include a reference source to support your answer. (b) Refer to AS/NZS 3000 and state THREE types of earthing conductors that are not required to be insulated. (3 marks) (1) (2) (3) 16

17 Question 5 continued (c) Refer to AS/NZS 3000 and state whether or not an RCCB type RCD can be used as the sole electrical protection for a final subcircuit. State a reason and the reference to support your answer. (d) Refer to AS/NZS 3000 and state the ONE restriction placed on a protective earthing conductor that originates at a distribution switchboard. 17

18 Question 6 (a) You are going to make additions and alterations to an existing 230V MEN domestic electrical installation. There is only one switchboard and there is no RCD protection on any of the final subcircuits. (i) You are required to install a new final subcircuit for the new range located in a different location to the original. The new range will be supplied via a socket outlet. Refer to AS/NZS 3000 and state the TWO conditions under which this subcircuit does not require RCD protection. (1) (2) (ii) A new socket outlet is to be installed in Zone 2 of a bathroom and supplied from an existing subcircuit. State TWO methods, either of which will provide RCD protection for this socket outlet. (1) (2) 18

19 Question 6 continued (b) A home dialysis unit is to be installed in a domestic residence. Refer to AS/NZS 3000 and state the THREE requirements for this type of installation. (3 marks) (1) (2) (3) _ (c) State the maximum permitted rated residual current of an RCD installed for: (i) Personal protection in a domestic installation. (ii) Personal protection in a medical-electrical installation. (iii) The protection of property. 19

20 Question 7 (a) A 5000 litre in-ground swimming pool is being installed outside a domestic residence. A block wall will run along one side of and 1.5 metres from the internal rim of the pool. All equipment external to the pool operates at 230V. (i) It is proposed to install a socket outlet on the block wall. It will be used solely for the connection of pool equipment. Refer to AS/NZS 3000 and state whether or not the socket outlet can be installed in this position. State a reason to support your answer. (ii) It is proposed to install a socket outlet in Zone 1 of the swimming pool. Refer to AS/NZS 3000 and state TWO methods, either of which can be used to provide the electricity supply to the socket outlet. (1) (2) 20

21 Question 7 continued (iii) It is proposed to install luminaires in Zone 0 of the swimming pool. Refer to AS/NZS 3000 and state THREE requirements apart from those relating to the electricity supply for the installation of the luminaires. (3 marks) (1) (2) (3) (b) Refer to AS/NZS 3000 and state the TWO general requirements relating to the installation of a wiring system for a swimming pool. (1) (2) 21

22 Question 7 continued (c) Refer to AS/NZS 3000 and state TWO protective measures that can be taken to prevent voltage gradients in a swimming pool. (1) (2) 22

23 Question 8 Refer to AS/NZS 3000 and calculate the maximum demand in amps of a 230V domestic installation with the following loads: Number Rating Equipment W Lighting points 10 75W Outdoor lighting discharge lamps 1 6kW Electric range 18 10A Double socket outlets 10 10A Single socket outlets 1 3KW Water storage heater 1 6kW Sauna Use the grid on the following page to perform the calculations. (10 marks) 23

24 Question 8 Equipment Load Group Calculation Load (A) Maximum demand 24

25 Question 9 You are wiring a new domestic residence that includes recessed luminaires and other permanently connected equipment. (a) Recessed Halogen lights are being installed. There are no manufacturers instructions with the lights and it is not possible to install the lights in fire-resistant enclosures. Refer to AS/NZS 3000 and state: (i) The clearance required above the recessed Halogen lights. (ii) The side clearance required between the recessed Halogen lights and a structural member. (iii) The clearance required between the recessed Halogen lights and thermal insulation. (iv) The clearance required between the recessed Halogen lights and the supply transformer. 25

26 Question 9 continued (b) Refer to AS/NZS 3000 and state the TWO requirements, either of which applies to the installation of festoon lighting. (1) (2) (c) Refer to AS/NZS 3000 and state TWO positions where the isolating switch for a room heater may be located. (1) (2) (d) Refer to AS/NZS 3000 and state the TWO methods of installing suitable warning signs drawing attention to the existence of under-floor heating cables. (1) (2) 26

27 For Candidate s Use For Examiner s Use Only Questions Answered Marks 1 In the box, write the number of EXTRA sheets you have used. Write NIL if you have not used any TOTAL 27