EST 2071

Candidate Code No.

For Board Use Only

Result Date Int

Result Date Int

ELECTRICAL SERVICE TECHNICIAN EXAMINATION

26 November 2016 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 based on correctness.

Do not use correcting fluid or correcting tape.

If a question can be answered from the Act, Regulations, Standard or Code of Practice it is recommended that the relevant clause or regulation number be stated in the reference space provided.

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 reprint dated 1 August 2014 or the Electricity (Safety) Regulations reprint dated 4 April 2016.

● AS/NZS 3000:2007 (incorporating amendments 1 and 2).

● AS/NZS 3760:2010

PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM (turn over)

EST 2071 – 26 NOVEMBER 2016 2

Question 1 (a) Refer to the Electricity (Safety) Regulations 2010 and define the term RCD

(2 marks) ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________

Ref: ……………………………………. (b) Refer to the Electricity (Safety) Regulations 2010 and state ONE safety

system that must be used when operating a 230V, Class I, handheld electrical appliance in a damp situation.

(2 marks) ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

Ref: ……………………………………. (c) A three-phase delta-connected motor is supplied by a four-core flexible

cord (three phases and earth). Refer to AS/NZS 3000 and state the colour coding and polarity for the

conductors of the flexible cord. (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

Ref: …………………………………………

(turn over)

EST 2071 – 26 NOVEMBER 2016 3

Question 1 continued (d) A three-phase 400V induction motor is controlled by a star/delta starter. How is the direction of rotation of the motor changed?

(2 marks)

____________________________________________________________

____________________________________________________________ (e) A replacement HRC fuse link must have characteristics similar to the

original fuse link. Two characteristics are current rating and voltage rating. State the TWO other electrical characteristics that must be checked for

similarity. (2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

(f) A circuit-breaker that is used as back-up protection for a motor has the markings 6 kA and 16A.

(i) Define the term 6 kA.

(1 mark) ________________________________________________________

________________________________________________________ ________________________________________________________ (ii) Define the term 16A.

(1 mark) ________________________________________________________

________________________________________________________

________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 4

Question 1 continued (g) The earth continuity test on a three-phase motor shows a protective

earthing conductor resistance of 0.15 Ω when measured between the earth pin of the plug and the frame of the motor.

Can the motor be returned to service? Give a reason to support your

answer. (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________ (h) A 400V, three-phase induction motor, controlled by a direct-on-line (DOL)

starter, has been operating normally and has been switched off. When restarted using the start button, the contactor closes, but as soon as

the start button is released again the contactor drops out of the circuit. State ONE cause for this type of fault.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(i) The New Zealand Multiple Earth Neutral system of single/three phase standard low voltage distribution requires four conductors – three phases and a neutral.

(i) State the voltage that exists between two phase conductors.

(1 mark) ________________________________________________________

(ii) State the voltage that exists between the neutral conductor and earth. (1 mark)

________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 5

Question 1 continued (j) State ONE reason why stop buttons; emergency stop buttons;

thermostats; or ripple control relays are not suitable for use as an isolation switch.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 6

Question 2 (a) In a thermal/electromagnetic MCB. (i) What type of fault causes the thermal mechanism to operate?

(1 mark) ________________________________________________________ (ii) How does the thermal mechanism operate when the fault in (a)(i) is

detected? (1 mark)

________________________________________________________ ________________________________________________________ (iii) What type of fault causes the electromagnetic mechanism to

operate? (1 mark)

________________________________________________________ (iv) How does the electromagnetic mechanism operate when the fault

in (a)(iii) is detected? (1 mark)

________________________________________________________ ________________________________________________________ (b) State the main purpose of an RCD found on a switchboard.

(2 marks)

____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 7

Question 2 continued (c) State the main purpose of an HRC fuse found on a switchboard.

(2 marks)

____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ (d) A rewireable fuse is being reloaded. State ONE reason why it is important

to thread the fuse wire from terminal to terminal through the tortuous path in the fuse carrier.

(2 marks) ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 8

Question 3 Introduction A 230V, hot water cylinder final subcircuit is protected by an MCB. The existing hot water cylinder has been disconnected from the non-lockable isolator. You are to connect a new hot water cylinder to the non-lockable isolator. The kW rating of the new MIMS element is the same as the existing cylinder. A new flexible cord has been connected to the new hot water cylinder Use the information in the introduction of this question to answer parts 3(a) and 3(b). (a) Refer to AS/NZS 3760 and describe the TWO instrument tests that need to

be carried out on the new hot water cylinder and flexible cord so it is safe to connect to the power supply. Include:

● The type of instrument used ● The test voltage applied - if applicable ● The expected test result ● Whether the test result is a minimum or maximum value

(6½ marks) Test 1 ____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

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____________________________________________________________

____________________________________________________________

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(turn over)

EST 2071 – 26 NOVEMBER 2016 9

Question 3 continued Test 2 ____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________ (b) The final subcircuit, or isolator, does not have tags attached. Describe the steps that you will take to ensure your own safety prior to

connecting the new hot water cylinder to the existing isolating switch. (3½ marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 10

Question 4 Introduction A three-phase motor is controlled by DOL starter that contains thermal overloads. The starter control circuit operates at 230V. The motor circuit is protected by HRC fuses. Use the information in the introduction to answer parts 4(a), 4(b), 4(c) and 4(d). (a) Draw and label the circuit diagram of the 230V DOL starter control circuit

that incorporates thermal overload protection. (4 marks)

(turn over)

EST 2071 – 26 NOVEMBER 2016 11

Question 4 continued (b) In the starter control circuit for a DOL starter, what is the purpose of the

hold-in contact? (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(c) A remote start/stop station has been connected in parallel with the stop

button in the DOL starter circuit. What effect would this have if the motor had to be stopped in an

emergency? (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________ (d) Describe how a thermistor would provide protection to the motor

(2 marks) ____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 12

Question 5 (a) (i) Draw and label a circuit diagram of a single-phase standard split-

phase motor. (3 marks)

(ii) State ONE device that can be used in a single-phase split-phase motor

in place of a centrifugal switch? (2 marks)

________________________________________________________

(b) State ONE reason why a single-phase standard split-phase motor would be replaced with a single-phase, capacitor-start motor.

(1 mark) ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 13

Question 5 continued (c) State ONE technical reason why universal motors are used in portable

power tools rather than induction motors. (2 marks)

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ (d) In a single-phase capacitor-start induction motor the capacitor became

short-circuited while the motor was running. Explain why the motor failed to start when it was switched off then

switched back on. (2 marks)

____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 14

Question 6 (a) State TWO checks of the test instruments that need to be carried out

before testing commences on live 230V appliances. (4 marks)

(1) ________________________________________________________

________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

________________________________________________________

(b) An electrical service technician used the prove-test-prove method to test for isolation on the supply side of an isolator by testing between each phase.

The electrical service technician dismantled the isolator and received an

electric shock. State ONE reason why the testing was ineffective.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 15

Question 6 continued (c) A three-phase MCB protects electrical equipment that is controlled by a

lockable isolating switch. The electrical equipment has been isolated. Describe TWO methods of ensuring the electrical equipment remains

isolated while the work site is left unattended. (2 marks)

(1) ________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

(d) Refer to AS/NZS 3000 and define the term isolated. (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

Ref: …………………………………………

turn over)

EST 2071 – 26 NOVEMBER 2016 16

Question 7 (a) Refer to the Electricity (Safety) Regulations 2010 and state TWO situations

where an electrical appliance is deemed electrically unsafe. (4 marks)

(1) ________________________________________________________

________________________________________________________

________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________ ________________________________________________________ ________________________________________________________

________________________________________________________

Ref: ………………………………………… (b) A 230V plug-in domestic electrical appliance has been repaired. Refer to the Electricity (Safety) Regulations 2010 and state TWO situations

the person who did the repair must ensure. (2 marks)

(1) ________________________________________________________

________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________ ________________________________________________________

Ref: …………………………………………

(turn over)

EST 2071 – 26 NOVEMBER 2016 17

Question 7 continued (c) Refer to the Electricity (Safety) Regulations 2010 and state TWO situations

where a portable RCD is deemed electrically unsafe. (4 marks)

(1) ________________________________________________________

________________________________________________________

________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________ ________________________________________________________ ________________________________________________________

________________________________________________________

Ref: …………………………………………

(turn over)

EST 2071 – 26 NOVEMBER 2016 18

Question 8 Introduction The figure below is a 230V class I oven with three compartments. There is one element in each compartment. ● Element 1 is 26.45 Ω ● Element 2 is 52.9 Ω ● Element 3 is 105.8 Ω

Use the information in the introduction to this question to answer parts 8(a), 8(b) and 8(c).

(turn over)

E

3 2 1

N

Control Switch Fuse

P

EST 2071 – 26 NOVEMBER 2016 19

Question 8 continued (a) Calculate the total power consumed by the oven when all switches are in

the on position. (4 marks)

(b) Calculate the current drawn by the oven when only element 2 and

element 3 are operating. (4 marks)

(turn over)

EST 2071 – 26 NOVEMBER 2016 20

Question 8 continued (c) Use calculations to show the maximum current that must be carried by

the flexible cord supplying the oven. (2 marks)

(turn over)

EST 2071 – 26 NOVEMBER 2016 21

Question 9 (a) A replacement flexible cord is being selected for a single-phase Class I,

heater rated at 2000W. (i) Which physical characteristic of the flexible cord determines whether

the cord can safely carry the full load current of the appliance? (1 mark)

________________________________________________________ (ii) Which physical characteristic of the flexible cord determines whether

the appliance can fully produce 2000W? (1 mark)

________________________________________________________ (iii) State ONE feature (other than the characteristics stated in (i) and (ii)

above) that may need to be considered in selecting the cord. (2 marks)

________________________________________________________ ________________________________________________________ ________________________________________________________ (b) A new three-pin plug has been fitted to a three-core PVC sheathed flexible

cord supplying a Class I electrical appliance. State ONE feature that needs to be considered when selecting the new

three-pin plug. (2 marks)

____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2071 – 26 NOVEMBER 2016 22

Question 9 continued (c) You need to replace the flexible cord of a 230V, 2kW, plug-in Class II

portable space heater. (i) Use calculations to determine the minimum current rating of the

flexible cord you should use. (2 marks)

(ii) For the flexible cord state ONE set of colour coding and polarity for

the conductor cores of the flexible cord. (2 marks)

________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________

EST 2071 – 26 NOVEMBER 2016 23

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

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