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EST 2041
Candidate Code No.
For Board Use Only
Result Date Int
Result Date Int
ELECTRICAL SERVICE TECHNICIAN EXAMINATION
15 May 2010
QUESTION AND ANSWER BOOKLET
Time Allowed: Two 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. 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 some of the following documents in this examination: Electricity Act 1992 reprint dated 19 August 2005 and the Electricity Amendment
Act 2006 or Electricity Act 1992 reprint dated 2008 and the Electricity Amendment Act 2006 or the Electricity Act 1992 reprint dated 1 April 2010
Electricity Regulations 1997 reprint dated 2 September 2005 or the Electricity (Safety) Regulations 2010
AS/NZS 3000:2000 and Amendments 1, 2, 3 and A or AS/NZS 3000:2007 and Amendment No 1
AS/NZS 3760:2003 and Amendment No 1 AS 60529 or AS 1939 Supplement 1-1990 NZECP 34 NZECP 54 PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM
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EST2041 – 15 MAY 2010 2
Question 1
(a) Refer to the Electricity Regulations, and briefly state the essential requirements of the term “electrically safe”.
(2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
Ref: …………….………………………………………….
(b) Which TWO of the following factors will not affect the voltage drop in a two
core flexible cord?
Insulation resistance
Resistance
Fusing factor Cross-sectional area
(2 marks)
(1) ________________________________________________________
(2) ________________________________________________________
(c) Briefly explain the operation of an energy controller (Simmerstat) when it
controls a heating load. (2 marks)
____________________________________________________________
____________________________________________________________
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EST2041 – 15 MAY 2010 3
Question 1 continued (d) A handheld electrical appliance used by a person who is partially
immersed in a conductive substance must be used in conjunction with an appropriate safeguard. Refer to the Electricity Regulations and state TWO such safeguards.
(2 marks)
(1) ________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Ref: …………….…………………………………………. (e) State the main characteristic that determines the maximum current a
flexible cord can carry safely without overheating. .
(2 marks) ____________________________________________________________ ____________________________________________________________
____________________________________________________________
(f) Refer to AS/NZS 3000 and briefly explain what is meant by a damp situation.
(2 marks) _____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
Ref: ………..………………………………………………
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EST2041 – 15 MAY 2010 4
Question 1 continued (g) An HRC fuse has blown on a three-phase switchboard. The single-phase
circuit protected by the fuse supplied a socket outlet. The electrical
appliance that was plugged into that socket outlet has been disconnected and tagged with an “out-of-service” tag.
When the fuse was replaced, the fuse blew again. What is the cause of the
fault and what action should be taken to rectify it?
(2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
(h) Refer to AS/NZS 3000 and state what is meant by Class I electrical
equipment? (2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
Ref: …………………………………………………………
(i) A Class II plug-in electrical appliance is supplied from a socket outlet and is
operating at full load. State the main electrical effect on the appliance if it
was supplied via an extra-long extension cord while operating at full load. (2 marks)
____________________________________________________________
____________________________________________________________
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EST2041 – 15 MAY 2010 5
Question 1 continued
(j) (i) Describe how you would reverse a single-phase capacitor-start induction motor.
(1 mark)
________________________________________________________
________________________________________________________
(ii) Describe how you would reverse a single-phase universal motor. (1 mark)
________________________________________________________
________________________________________________________
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EST2041 – 15 MAY 2010 6
Question 2
(a) Refer to the Electricity Regulations and state what is meant by the term “MEN system”
Note: You must state the full definition to gain marks. (2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
(b) State TWO reasons why the neutral in the MEN system is multiple-earthed.
(2 marks)
(1) ________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
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EST2041 – 15 MAY 2010 7
Question 2 continued
(c) Draw a circuit diagram showing three-phase, 4 wire, MEN distribution lines supplying:
• A single-phase consumer installation.
• A three-phase consumer installation.
You need to show for each installation, the main switch, neutral and earth
bar connections, MEN link and earth electrode
You do not need to show metering, water heating control and fuses and
final subcircuit conductors.
Note: It is recommended that you label your diagram.
(6 marks)
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EST2041 – 15 MAY 2010 8
Question 3
(a) Refer to the Electricity Regulations and state the Standard to which a 230V, Class I, plug-in under-sink electric water heater must be tested following completion of repairs?
(1 mark)
____________________________________________________________
Ref: …………………………………………………………
(b) The 230V, Class I, plug-in under-sink electric water heater has an MIMS
element. Refer to the Standard you have stated in (a) and complete the following table in relation to the tests required to be carried out using test instruments.
Note: The tests are to be carried out while the water heater is
disconnected from the electricity supply.
(4 marks)
Test 1
Type of test ________________________________________
Instrument used ________________________________________
Permitted test result ________________________________________
Is the permitted test result a minimum or maximum value? _____________
Ref: ………..………………………………………………
Test 2
Type of test ________________________________________
Instrument used ________________________________________
Permitted test result ________________________________________
Is the permitted test result a minimum or maximum value? _____________
Ref: ………..………………………………………………
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EST2041 – 15 MAY 2010 9
Question 3 continued
(c) Refer to the Standard you have stated in (a) above and describe FOUR visual checks (inspections) that must be carried out on the 230V, Class I, plug-in under-sink electric water heater
Note: The visual checks (inspections) must relate specifically to
the 230V, Class I, plug-in electric water heater (2 marks)
(1) ________________________________________________________
________________________________________________________ ________________________________________________________
(2) ________________________________________________________
________________________________________________________
________________________________________________________
(3) ________________________________________________________
________________________________________________________
________________________________________________________
(4) ________________________________________________________
________________________________________________________
________________________________________________________
Ref: ………..………………………………………………
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EST2041 – 15 MAY 2010 10
Question 3 continued
(d) Briefly describe how you would carry out the tests on the water heater that you have stated in (b)
(3 marks)
Test 1
____________________________________________________________
____________________________________________________________
____________________________________________________________
Test 2
____________________________________________________________
____________________________________________________________
____________________________________________________________
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EST2041 – 15 MAY 2010 11
Question 4
(a) The following diagram shows a 230 V waveform.
(i) Is it an a.c. voltage or d.c. voltage waveform?
(1 mark)
________________________________________________________
(ii) Name the numbered items and state the value that applies to each item
(3 marks)
Item Name Value
1
2
3
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100
1
2
3
0
200
400
300
V
EST2041 – 15 MAY 2010 12
Question 4 continued
(b) The New Zealand single phase 230V a.c. supply operates at a frequency of 50 Hz. Briefly describe the meaning of the term Hz.
(1 mark)
____________________________________________________________
____________________________________________________________
____________________________________________________________
(c) It is necessary to have a reliable protective earthing conductor for a Class I electrical appliance.
(i) State TWO reasons why a protective earthing conductor contributes to the electrical safety of a Class I electrical appliance.
(2 marks)
(1) ____________________________________________________
____________________________________________________
____________________________________________________
(2) ____________________________________________________
____________________________________________________
____________________________________________________
(ii) You have completed repairing a plug-in, Class I 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 protective earthing conductor test result complies with AS/NZS 3760.
(3 marks)
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________ ________________________________________________________
________________________________________________________
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EST2041 – 15 MAY 2010 13
Question 5
Note: Read the entire question before commencing. In a bakery a three-phase oven comprising three single-phase 6 kW elements is
faulty. The oven is controlled by a contactor. Both the oven and contactor are controlled by an adjacent isolating switch. The manager has told you that:
One HRC fuse blew. When it was replaced it blew immediately.
A week later another HRC fuse blew. When it was replaced it blew
immediately. One element in the oven operates.
Warning: If any part of your answer is dangerous or hazardous, you will get no marks for this question.
(a) Describe how you would safely isolate the oven.
(3 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
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EST2041 – 15 MAY 2010 14
Question 5 continued
(b) This is a block diagram of the oven and associated cables and equipment
Parts A, B and D are not faulty. The HRC fuses are correctly rated and are
not faulty.
(i) You need to test each one of the faulty parts. Which THREE parts of the circuit would you disconnect to enable testing to be carried out?
(1½ marks)
Part 1 ________________________________________________
Part 2 ________________________________________________
Part 3 ________________________________________________
(ii) What type of test would you carry out on each of the three parts you identified in (b)(i)?
(1 mark)
________________________________________________________
(iii) What type of test instrument would you use?
(1 mark)
________________________________________________________
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A B C D E F
A Circuit between switchboard
and isolator
B Isolator
C Circuit between isolator and
contactor
D Contactor
E Circuit between contactor and
oven
F Oven
EST2041 – 15 MAY 2010 15
Question 5 continued
(iv) Describe how you would test each of the parts you have identified in (b)(i). For each part include the expected test if the fault was in that part
(3½ marks)
Part 1
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Part 2
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Part 3
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
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EST2041 – 15 MAY 2010 16
Question 6
(a) An electric motor that is supplied from a circuit protected by MCBs is required to be isolated. Two precautions must be taken to secure the isolation as the motor isolator is not located adjacent to the motor. State
TWO types of precautions that can be taken. (2 marks)
(1) ________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
(b) State the TWO reasons why the prove-test-prove method of testing for
isolation is used. (2 marks)
(1) ________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
(c) State TWO circumstances where an isolating switch would carry two safety warning tags.
(2 marks)
(1) ________________________________________________________
________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
________________________________________________________
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EST2041 – 15 MAY 2010 17
Question 6 continued
(d) A three phase fixed wired electrical machine has been isolated using the prove-test-prove method. Describe FOUR methods of ensuring the continued isolation of the machine.
(4 marks)
(1) ________________________________________________________
________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
________________________________________________________
(3) ________________________________________________________
________________________________________________________
________________________________________________________
(4) ________________________________________________________
________________________________________________________
________________________________________________________
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EST2041 – 15 MAY 2010 18
Question 7
(a) Electrical equipment designed for use in damp situations have an IP rating – an International Protection rating or Ingress protection rating. An IP rating consists of the initials IP followed by two numbers.
(i) Refer to AS1939; AS 60529 or AS/NZS 3000 and state what is meant
by the term “IP rating”. (2 marks)
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Ref: ………..………………………………………………
(ii) Explain what the first number after the letters IP indicates.
(2 marks)
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Ref: ………..………………………………………………
(iii) Explain what the second number after the letters IP indicates.
(2 marks) ________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Ref: …………………………………………………………
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EST2041 – 15 MAY 2010 19
Question 7 continued
(b) Refer to AS1939, AS 60529 or AS/NZS 3000 and describe the level of protection offered by fittings rated at IP34.
(2 marks)
3 ________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
4 ________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
Ref: ………..………………………………………………
(c) You have been requested to replace a faulty motor and control switch for a
swimming pool pump. Due to age, neither the motor or control switch have any visible markings on them.
The motor is in Zone 1 of the swimming pool.
The control switch is in Zone 2 of the swimming pool.
Refer to AS/NZS 3000 and state: (i) The minimum IP rating requirement for the replacement pump motor.
(1 mark)
________________________________________________________
(ii) The minimum IP rating requirement for the replacement control
switch.
(1 mark)
________________________________________________________
Ref: ………..………………………………………………
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EST2041 – 15 MAY 2010 20
Question 8
(a) 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?
(1 mark)
____________________________________________________________
____________________________________________________________
(b) State TWO ways in which the effect in (a) above can be reduced.
(2 marks) (1) ________________________________________________________
________________________________________________________
(2) ________________________________________________________
________________________________________________________
(c) All flexible cords are given a current rating. What does current rating mean?
(2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
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EST2041 – 15 MAY 2010 21
Question 8 continued
(d) A 230V, single phase, three-core flexible cord supplying a Class I electrical appliance is required to be replaced. In the table below, state the colour coding acceptable in New Zealand and the polarity for the replacement
cord.
To gain the marks for this question you must accurately state all of the colours and polarity.
(3 marks)
Existing cord
conductor colours
Acceptable Colours
in New Zealand
Polarity
Green
Black
Red
(e) A microgap switch is rated to switch a circuit at 10 amp 230V a.c. only.
State ONE reason why this switch would not be suitable for use on a d.c.
circuit of similar current and voltage. (2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
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EST2041 – 15 MAY 2010 22
Question 9 A fixed-wired small printing press, driven by a three-phase electric motor is supplied by PVC cables enclosed in a flexible steel conduit. It has been operating safely for some months, but the operator has now reported the MCB protection occasionally tripping. When reset, the MCB trips again. The MCB is not faulty. The MCB is correctly rated for the circuit it protects. The cables to the motor are not faulty. You have been required to find the problem and have safety tagged the circuit and confirmed by testing, that the supply is isolated. (a) You carried out an insulation resistance test. (i) State the type of instrument and test voltage used.
(1 mark) ________________________________________________________ (ii) Briefly describe how you carried out this test. Include any desired test
result (3 marks)
________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ (iii) State the reason why the MCB tripped if an unsatisfactory insulation
resistance test result was obtained. (2 marks)
________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________
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EST2041 – 15 MAY 2010 23
Question 9 continued
(b) (i) Describe the test you would carry out to confirm that the motor is functionally earthed. Identify the type of instrument used and any minimum or maximum test values that are applicable.
(2 marks)
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
(ii) Describe how the test described in (b)(i) contributes to the safety of
the motor.
(2 marks)
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
________________________________________________________
EST2041 – 15 MAY 2010 24
For Candidate’s Use For Examiner’s Use Only
Questions
Answered
Marks
1
2
3
4
In the box, write the
number of EXTRA
sheets you have used. Write NIL if
you have not used
any
5
6
7
8
9
TOTAL
