EST 2055

Candidate Code No.

For Board Use Only

Result Date Int

Result Date Int

ELECTRICAL SERVICE TECHNICIAN EXAMINATION 29 June 2013

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.

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 will need to use the following documents in this examination:

Electricity (Safety) Regulations 2010 and Amendment No 1

AS/NZS 3000:2007 and Amendments 1, 2 and A

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

EST 2055 – 29 JUNE 2013 2

Question 1 (a) A 230V/240V electric heater has a resistance of 24Ω when measured with

an ohmmeter. The heater draws 10A when plugged into a 240V supply: Calculate the current the heater will draw when plugged into a 230V supply.

(2 marks) (b) Refer to AS/NZS 3000 and define the term Class II equipment.

(2 marks) ____________________________________________________________ ____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

Ref: ………………………………………………

(turn over)

EST 2055 – 29 JUNE 2013 3

Question 1 continued (c) When replacing an HRC fuse which has blown, the replacement must have

FOUR electrical characteristics that are similar to the original fuse. State those four characteristics.

(2 marks) (1) ________________________________________________________ (2) ________________________________________________________ (3) ________________________________________________________ (4) ________________________________________________________ (d) Refer to AS/NZS 3000 and briefly explain the term damp situation.

(2 marks) ____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

Ref: ………………………………………………

(e) (i) The connections to the start winding in a motor are changed. What

type of motor is being reversed? (1 mark)

________________________________________________________ ________________________________________________________ (ii) The connections to the field winding in a motor are changed. What

type of motor is being reversed? (1 mark)

________________________________________________________

________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 4

Question 1 continued (f) Refer to the Electricity (Safety) Regulations 2010 and define the following

terms. (i) Earthed.

(1 mark) ________________________________________________________ ________________________________________________________

Ref: …………………………………………

(ii) Standard low voltage in a multi-phase MEN system.

(1 mark) ________________________________________________________ ________________________________________________________

Ref: …………………………………………

(g) A three-phase motor is connected to the electricity supply by three-core

and earth flexible cord in which each conductor is identified by means of colour.

Refer to AS/NZS 3000 and state the requirements that apply to the colours

and polarity of the flexible cord. (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

Ref: …………………………………………

(turn over)

EST 2055 – 29 JUNE 2013 5

Question 1 continued (h) A 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.

Note: 1. The voltage level is normal. 2. The protection is correctly rated and is not faulty. State TWO causes for this type of fault.

(2 marks)

(1) ________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

(i) You have repaired a 400V, three-phase, Class I electrical appliance that incorporates a control switch and now need to test the appliance to ensure it is electrically safe before you connect it to the electricity supply.

State FOUR tests using test instruments that you would carry out on the

appliance before connecting it to the electricity supply. (2 marks)

(1) ________________________________________________________

(2) ________________________________________________________ (3) ________________________________________________________

(4) ________________________________________________________ (j) What type of protection device is installed on three-phase final subcircuits

to specifically provide protection for: (i) The loss of one phase on the electricity supply. (1 mark)

________________________________________________________

(ii) The reversal of phase rotation on the electricity supply. (1 mark)

________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 6

Question 2 (a) (i) Draw and label a 230V a.c. waveform that shows: The peak voltage The RMS voltage The time interval

(2½ marks)

(ii) State the values for:

(1½ marks)

1. Peak voltage ________________________________________

2. RMS voltage ________________________________________ 3. Time interval ________________________________________ (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)

____________________________________________________________

____________________________________________________________ ____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 7

Question 2 continued (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 ensure the protective

earthing conductor test result is less than 1Ω so the appliance can be returned to service.

(3 marks)

________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 8

Question 3 Introduction A three-phase, 400V induction motor that is controlled by a star/delta starter has been removed from an industrial machine for cleaning and checking. Before reconnecting the motor to the machine tests need to be carried out to ensure the motor is safe to connect to the electricity supply. Use the information in the introduction to this question to answer parts 3(a), 3(b), 3(c) and 3(d). (a) Describe how you would carry out an insulation resistance test using a

multi-function test instrument that has the relevant functions. Within the description state:

The function selected on the multi-function test instrument The range selected on the multi-function test instrument How the testing is carried out A test result for each test that permits the motor to be returned to

service (5 marks)

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 9

Question 3 continued (b) The motor has thermistors embedded in the windings to provide protection

against overheating. What precaution needs to be taken before carrying out the insulation resistance test to avoid damage to the thermistors.

(1 mark) ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(c) State the actions you would take to ensure it is safe to reinstall the motor in the industrial machine.

(2 marks) ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(d) State TWO other tests, using a test instrument that should be taken once

the motor has been connected to the machine. (2 marks)

(1) ________________________________________________________ (2) ________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 10

Question 4 (a) Define the term current rating as it applies to an HRC fuse.

(2 marks) ____________________________________________________________

____________________________________________________________

(b) An HRC fuse on a switchboard protects a final sub-circuit. State the reason why the fuse blows before the circuit has reached full-

load current. (1 mark)

____________________________________________________________

____________________________________________________________ (c) An HRC fuse on a switchboard protects a final sub-circuit. State the reason why the circuit has been damaged under fault conditions.

(1 mark) ____________________________________________________________

____________________________________________________________ (d) A no-voltage relay protects a motor circuit. (i) State the type of fault a no-voltage relay is specifically designed to

protect against. (1 mark)

________________________________________________________

________________________________________________________

(ii) State what happens when the no-voltage relay detects a fault.

(1 mark) ________________________________________________________

________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 11

Question 4 continued (e) A phase reversal relay protects a motor circuit. (i) State the type of fault a phase reversal relay is specifically designed

to protect against. (1 mark)

________________________________________________________

________________________________________________________

(ii) State what happens when the phase reversal relay detects a fault.

(1 mark) ________________________________________________________

________________________________________________________ (f) Describe how the internal mechanism of a thermal type circuit breaker

operates when an overload occurs. (2 marks)

____________________________________________________________

____________________________________________________________ ____________________________________________________________

____________________________________________________________ ____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 12

Question 5 (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) Define the term current rating as it applies to a flexible cord.

(2 marks) ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ (d) A 230V, single phase, three-core flexible cord supplying a Class I electrical

appliance is required to be replaced. Refer to AS/NZS 3000 and state ONE set of colour coding and polarity for

the conductors of the flexible cord. (3 marks)

____________________________________________________________ ____________________________________________________________ ____________________________________________________________

Ref: …………………………………………

(turn over)

EST 2055 – 29 JUNE 2013 13

Question 5 continued (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)

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 14

Question 6 (a) The diagram below shows a control circuit for a three-phase DOL motor

starter. (i) Name the numbered parts of the circuit.

(4 marks)

1 ____________________________________________________

2 ____________________________________________________

3 ____________________________________________________

4 ____________________________________________________

5 ____________________________________________________

6 ____________________________________________________

7 ____________________________________________________

8 ____________________________________________________ (ii) State a typical operating voltage for the circuit

(1 mark)

________________________________________________________

(turn over)

1

2

3 4

5

6

7 8

EST 2055 – 29 JUNE 2013 15

Question 6 continued (b) The motor can be protected by a thermal overload or a thermistor. Explain how a thermal overload operates to protect the motor.

(2 marks) ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ (c) The motor can be protected by a thermal overload or a thermistor. Explain how a thermistor operates to protect the motor.

(2 marks) ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ (d) Supply lines 1 and 3 have been reversed at the output terminals of a DOL

starter supplying a 3-phase induction motor when the wiring was re-connected. What will happen when this induction motor is livened?

(1 mark) ____________________________________________________________

____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 16

Question 7 (a) You are connecting test instruments to measure voltage and current values

of a live 230V electrical appliance. State FOUR precautions relating to the test instruments that will promote

personal safety. Note: 1. All the necessary safety equipment (overalls, rubber mats

etc.) is available. 2. Set procedures are available. 3. All conductive items (e.g., rings) have been removed.

(4 marks) (1) ________________________________________________________

________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

________________________________________________________

(3) ________________________________________________________

________________________________________________________

________________________________________________________

(4) ________________________________________________________

________________________________________________________

________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 17

Question 7 continued (b) An electrical service technician used a multi-meter to test for isolation on

the supply side of a three-phase isolator using the following procedure: A test on an independent live source confirmed that the meter worked

correctly. A test between each phase showed no reading on the meter. Another test on an independent live source confirmed that the meter

still worked correctly. The electrical service technician dismantled the isolator and received an

electric shock. Explain why the testing was ineffective.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(c) Explain how the prove test prove procedure is carried out. (3 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

turn over)

EST 2055 – 29 JUNE 2013 18

Question 7 continued (d) Describe ONE method of ensuring the continued isolation of a fixed wired

electrical appliance after you have attached a danger tag to the isolating switch.

(1 mark)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 19

Question 8 Introduction An electrical service technician has disconnected and repaired a single-phase, 230V industrial printing press in a print shop. The flexible cord is connected to the press. The press is to be connected via the flexible cord to a terminal box

mounted on an adjacent pillar There is a lockable isolator adjacent to the terminal box. The isolator is in the OFF position, but it is not locked and there are no

danger tags. You are required to reconnect and recommission the printing press. Use the information in the introduction to this question to answer parts 8(a), 8(b) and 8(c). (a) Before you connect the printing press to the terminal box. Describe the procedure you would take to ensure your own safety before

recommissioning the printing press. (2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 20

Question 8 continued (b) Before you connect the printing press to the terminal box. Describe the TWO tests using the instruments you need to carry out to

ensure the printing press is safe to reconnect to the electricity supply. Include the type of instrument used, test voltage (if applicable) and a test result that allows the press to be returned to service.

(7 marks) ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 21

Question 8 continued (c) After you have connected the printing press to the terminal box State TWO safety checks you would make before putting the press back in

service. (1 mark)

(1) ________________________________________________________ ________________________________________________________ (2) ________________________________________________________ ________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 22

Question 9 (a) (i) Sketch and label a circuit diagram of a single-phase capacitor-start

motor. (3 marks)

(ii) Describe how the direction of rotation can be reversed for single-phase

capacitor-start motor. (1 mark)

________________________________________________________

________________________________________________________

________________________________________________________ (iii) Describe the purpose of the capacitor in a single-phase capacitor-start

motor. (2 marks)

________________________________________________________

________________________________________________________

________________________________________________________

(turn over)

EST 2055 – 29 JUNE 2013 23

Question 9 continued (b) A small electric motor has a nameplate that reads:- Voltage 230 Phases 1 Horsepower 0.75 Speed 1425 r.p.m. Calculate the current drawn by the motor.

(3 marks) (c) A lightly-loaded single-phase capacitor start motor has been running

normally for 1 hour but then starts to slow. Once it slows down, it starts again. It keeps slowing down, then starting

again until it is switched off. State the cause of the fault. (1 mark)

____________________________________________________________

____________________________________________________________

EST 2055 – 29 JUNE 2013 24

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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