EIN 08

Candidate Code No.

For Board Use Only

Result Result

Date Date

Int Int

ELECTRICAL INSTALLER THEORY EXAMINATION

21 June 2014

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 on this paper.

Answer all questions.

The pass mark for this examination is 60 marks.

Use a pen for written answers. Do not use a pencil or a red pen.

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.

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.

Candidates are not permitted to use any Act, Regulation, Standard, Code of Practice, Handbook or other reference text in this examination.

PLEASE HAND THIS PAPER TO THE SUPERVISOR BEFORE LEAVING THE ROOM.

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Question 1

(a) (i) An insulation resistance test is being carried out on a 400V, Class 1, three-phase appliance.

(A) State the minimum acceptable insulation resistance for the appliance if it does not incorporate MIMS elements.

(½ mark)

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(B) State the minimum acceptable insulation resistance for the appliance if it incorporates MIMS elements.

(½ mark)

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(ii) Testing is being carried out to test the integrity of the insulation of a 230V, Class 1, single-phase appliance that does not incorporate MIMS elements.

(A) State the minimum acceptable insulation resistance test for the appliance.

(½ mark)

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(B) State the maximum acceptable earth leakage test result for the appliance.

(½ mark)

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(b) State TWO reasons why reduced-voltage starting of a large three-phase induction motor may be required.

(2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

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EIN08-QUESTIONS – 21 JUNE 2014 2

Question 1 continued

(c) With reference to a three-phase system of supply, explain the term phase sequence.

(2 marks)

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(d) State the main reason why it is important to consider the category of duty when selecting a protective device.

(2 marks)

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(e) A Residual Current Circuit Breaker (RCCB) is installed in a single-phase final subcircuit.

State TWO other protective devices, either of which is needed to provide electrical protection for the final subcircuit.

(2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

(f) Define the term inverse time-current characteristic as it applies to HRC fuses and MCBs

(2 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 3

Question 1 continued

(g) State the TWO types of operation employed by most MCBs. (2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

(h) State the TWO types of iron losses in the magnetic core of a power transformer.

(2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

(i) A three-phase induction motor normally runs on full-load. It has been serviced and you are re-commissioning it. When you load test the motor you find that it is now required to run lightly loaded.

State why it is not desirable to allow a motor to run lightly loaded when it normally runs on full load.

(2 marks)

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(j) The tests on a three-phase, star-connected squirrel cage motor show the following readings:

L1 – L2 20Ω L1 – L3 open circuit L2 – L3 open circuit

State the most likely fault indicated by these readings. (2 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 4

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Question 2

(a) (i) State the main reason for carrying out an earth fault loop impedance test on a single-phase final subcircuit supplying a socket outlet.

(2 marks)

(ii) Describe how the earth fault loop impedance tester is connected. (½ mark)

(b) (i) State the main reason for carrying out an RCD test on a single-phase final subcircuit supplying a socket outlet.

(1 mark)

(ii) Describe how the RCD tester is connected. (½ mark)

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EIN08-QUESTIONS – 21 JUNE 2014 5

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Question 2 continued

(c) Explain why Portable Residual Current Devices (PRCDs) used in New Zealand are required to be voltage dependent.

(1 mark)

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(d) (i) Describe how the prove test prove method of testing for isolation is carried out

(3 marks)

(ii) Why is it important to use the prove test prove method before working on electrical equipment?

(2 mark)

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EIN08-QUESTIONS – 21 JUNE 2014 6

Question 3

(a) Use the information given on this name plate to answer questions 3(a)(i), 3(a)(ii) and 3(a)(iii).

Ins.

Type MOT 112M Year.No. 1996042657

kW 4.0 kW HzH.P 50

R.P.M 1440 Ph. F3 -

Amb. Temp η %.Cos θ 0.82

Duty S1 Protection. IP 53

V 415

A 8.52

V

A

(i) Calculate the motor efficiency (4 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 7

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Question 3 continued

(ii) Calculate the percentage slip at full load (2 marks)

(iii) The motor is rated IP53. The letters IP stand for International (Ingress) Protection. Explain what is meant by the term IP.

(2 marks)

(b) The motor is to be started direct-on-line and protected by a thermal overload unit. The motor final subcircuit is protected by HRC fuses.

Explain why both of the protection devices are required.

(i) Thermal overload (1 mark)

(ii) HRC fuses (1 mark)

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EIN08-QUESTIONS – 21 JUNE 2014 8

Question 4

(a) A 400V, three-phase, four-wire installation has the following resistive loads on each phase:

Red 60kW White 40kW Blue 82kW

Determine the neutral current in amps. A scaled diagram may be used. (4 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 9

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Question 4 continued

(b) State TWO technical reasons why it is important to balance single-phase loads on a star-connected three-phase installation.

(2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

(c) State the formula used to determine the power consumed by:

(i) An inductive three-phase load. (1 mark)

(ii) A resistive single-phase load. (1 mark)

(d) A 230V, plug-in heater has an output of 2kW. The supply voltage to the heater fluctuates between 230V to 240V.

Describe the effect this voltage fluctuation has on the power output of the heater elements.

(2 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 10

Question 5

Introduction

You have been called to a fixed-wired concrete-making vibrating plant where a staff member received an electric shock off the frame of the plant.

The vibrating plant is driven by a 400V, three-phase, 1.5kW induction motor controlled by a DOL starter. The motor and starter are controlled by an adjacent lockable isolator.

Use the information in the introduction to this question to answer parts 5(a), 5(b) and 5(c).

(a) Describe how you will isolate the vibrating plant so testing can be carried out to locate the fault.

(3½ marks)

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EIN08-QUESTIONS – 21 JUNE 2014 11

Question 5 continued

(b) The vibrating plant has been isolated.

Describe how you will carry out testing to locate the fault. Include in the description:

The type of test instrument used The test voltage Where on the vibrating plant the testing takes place How the testing is carried out The expected test result when the fault is located.

(4 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 12

Question 5 continued

(c) The fault on vibrating plant has been repaired and the plant reconnected to the supply.

Describe the testing you need to carry out to ensure that in the event of a fault developing on the motor, the motor electrical protection will operate.

Include in your description:

The type of instrument used How the test is carried out A test result that will permit the motor to be livened

(2½ marks)

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EIN08-QUESTIONS – 21 JUNE 2014 13

Question 6

Introduction

The figure below represents 3 fluorescent lights supplied from a 230V MEN supply.

Switchboard

16A MCB

Light switch

Fitting A

1A 1A 1A

Fitting B Fitting C

Active (Phase)

Neutral

RCD

Earth

The fuses in the light fittings are HRC fuses.

Use the information in the introduction to this question to answer parts 6(a), 6(b), 6(c), 6(d) and 6 (e)

(a) (i) Which parts of the circuit are protected by the RCD. (1 mark)

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(ii) What type of fault does the RCD provide protection for? (1 mark)

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EIN08-QUESTIONS – 21 JUNE 2014 14

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Question 6 continued

(b) (i) Which parts of the circuit are protected by the MCB. (1 mark)

(ii) What types of faults does the MCB provide protection for? (1 mark)

(c) (i) Which parts of the circuit are protected by the HRC fuse in Fitting A? (1 mark)

(ii) What types of fault does this fuse provide protection for? (1 mark)

(d) How is discrimination achieved in this circuit? (2 marks)

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(e) State TWO reasons why the fuses in the fittings must not be shorted out or increased in current rating.

(2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

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EIN08-QUESTIONS – 21 JUNE 2014 15

Question 7

(a) When carrying out testing on a 230V final subcircuit, which Standard and section of that Standard details the tests and checks required to be carried out?

(1 mark)

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(b) The two figures below represent the front view of two single-phase socket outlets. Both socket outlets are connected to a standard low voltage supply.

(3 marks)

Label the polarity of the socket outlet connections on the figures.

Note: You must show the polarity completely correct to gain marks.

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EIN08-QUESTIONS – 21 JUNE 2014 16

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Question 7 continued

(c) You are using a voltage tester on the front of a 230V switched socket outlet to ensure power is present.

Note: The voltage tester is operating correctly. (3 marks)

(i) What voltage would you expect to find with the switch OFF:

Between Active – Neutral ________________________________

Between Active – Earth ________________________________

Between Neutral – Earth ________________________________

(ii) What voltage would you expect to find with the switch ON:

Between Active – Neutral ________________________________

Between Active – Earth ________________________________

Between Neutral – Earth ________________________________

(d) You are using a voltage tester on the front of a 230V switched socket outlet to ensure power is present and get the following results.

Test between Socket Terminals

Voltages Switch OFF

Voltages Switch ON

Active - Neutral 0V 230V

Active - Earth 0V 0V

Neutral - Earth 0V 0V

Note: The voltage tester is operating correctly.

State TWO reasons why you would get these readings? (2 mark)

(1) ________________________________________________________

(2) ________________________________________________________

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EIN08-QUESTIONS – 21 JUNE 2014 17

Question 7 continued

(e) You are using a voltage tester on the front of a 230V switched socket outlet to ensure power is present and get the following results:

Test between Socket Terminals

Voltages Switch OFF

Voltages Switch ON

Active - Neutral 0V 230V

Active - Earth 0V 0V

Neutral - Earth 230V 230V

Note: The voltage tester is operating correctly.

State the reason why you would get these readings. (1 mark)

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EIN08-QUESTIONS – 21 JUNE 2014 18

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Question 8

(a) The figure below represents the components of a DOL starter with a 400V control circuit and a remote stop/start station:

L1, L2, and L3 represent the three-phases connected to the main contacts.

U, V and W represent the three conductors from the thermal overloads to the motor

(i) Draw the conductors on the figure to complete a working 400V control circuit.

(2 marks)

L1 L2 L3

C4

U V W

(ii) State the purpose of the component labelled C4. (1 mark)

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EIN08-QUESTIONS – 21 JUNE 2014 19

Question 8 continued

(b) Electronic starters are often used with three-phase a.c. induction motors.

Explain how the operation of an a.c. variable speed controller is different to the operation of an electronic soft starter.

(2 marks)

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(c) Explain the term ramp time as it relates to an a.c. variable speed controller.

(1 mark)

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(d) A 400V, three-phase motor is started with a DOL starter. When started, the motor draws 90A and produces 200% full-load torque.

Calculate the starting current if the same motor is started with a star/delta starter.

(2 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 20

Question 8 continued

(e) A 400V, three-phase motor is started with a DOL starter. When started, the motor draws 90A and produces 200% full-load torque.

Calculate the percentage (%) of starting torque if the same motor is started with an auto-transformer starter with an 80% tap.

(2 marks)

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EIN08-QUESTIONS – 21 JUNE 2014 21

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Question 9

(a) (i) Sketch a circuit diagram of a single–phase, capacitor-start induction motor.

(3 marks)

(ii) State ONE advantage that a single–phase, capacitor-start induction motor has when compared to other single-phase induction motors.

(1 mark)

(iii) Describe how to change the direction of rotation of a single–phase, capacitor-start induction motor.

(½ mark)

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EIN08-QUESTIONS – 21 JUNE 2014 22

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Question 9 continued

(b) (i) Sketch a circuit diagram of a single–phase permanently-split capacitor motor.

(3½ marks)

(ii) State ONE advantage that a single–phase permanently-split capacitor motor has when compared to other single-phase induction motors.

(1 mark)

(iii) Describe how to change the direction of rotation of a single–phase permanently-split capacitor motor.

(1 mark)

EIN08-QUESTIONS – 21 JUNE 2014 23

For Candidate’s Use

In the box, write the number of EXTRA sheets you have used. Write NIL if you have not used any

For Examiner’s Use Only Questions Answered

Marks

1

2

3

4

5

6

7

8

9

TOTAL

EIN08-QUESTIONS – 21 JUNE 2014 24