ein 03 questions 19 nov 2011

7/27/2019 EIN 03 Questions 19 Nov 2011

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EIN03

Candidate Code No.

For Board Use Only

Result

Date

Int

Result

Date

Int

ELECTRICAL INSTALLER THEORYEXAMINATION

19 November 2011

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 todo 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. Marksare 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 fullmarks.

Non-programmable calculators may be used.

Warning You could get 0 marks for any question, or part of a question, if you showanything hazardous or dangerous in your answer.

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

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

(turn over)


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EIN03- QUESTIONS 19 NOVEMBER 2011 2

Question 1

(a) (i) An earth continuity (protective earthing) test has been carriedout on a repaired 230V, Class I, plug-in electrical appliance.

State an acceptable test result value for the earth continuity testthat will permit the electrical appliance to be returned to service.

(1 mark)

________________________________________________________

(ii) An insulation resistance test has been carried out on a repaired230V, Class II, plug-in electrical appliance.

State an acceptable test result value for the insulation resistancetest that will permit the electrical appliance to be returned to service.

(1 mark)

________________________________________________________

(b) (i) State the TWO functions that operate in a MCB.(1 mark)

(1) ____________________________________________________

(2) ____________________________________________________

(ii) Define the term AC 80 as found on an HRC fuse cartridge.(1 mark)

________________________________________________________

________________________________________________________

(turn over)


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Question 1 continued

(c) (i) State the TWO main functions of a choke (ballast) in a fluorescentlight fitting?

(1 mark)

(1) ____________________________________________________

____________________________________________________

(2) ____________________________________________________

____________________________________________________

(ii) State TWO factors that reduce the life of an incandescent lamp(1 mark)

(1) ____________________________________________________

(2) ____________________________________________________

(d) In the New Zealand MEN system the neutral is earthed at the star pointof a transformer; on the distribution system; and at the main switchboardof an installation.

State the TWO main reasons why the neutral is earthed in the NewZealand MEN system

(2 marks)

(1) ________________________________________________________

________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

________________________________________________________

(turn over)


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(e) A three-phase, fixed-wired electrical appliance that has been operatingnormally is to be removed for maintenance.

An isolating switch has been turned off. A voltage test was carried out atthe appliance terminals to test for isolation.

The testing showed terminals to be live. State TWO possible causes forthis situation.

(2 marks)

(1) ________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

(f) The tests on a star-connected squirrel cage motor show the followingreadings:

L1 L2 20L1 L3 open circuitL2 L3 open circuit

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

____________________________________________________________

____________________________________________________________

(g) One reason why the metal frame of a Class I electrical appliance is earthedis to ensure the operation of a protective device under fault conditions.

State ONE other reason why the metal frame of a Class I electricalappliance is earthed.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)


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(h) State the reason why a run capacitor is fitted to a single-phase split-phase induction motor.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(i) (i) Define the term pullout torque as it applies to an a.c. inductionmotor?

(1 mark)

________________________________________________________

________________________________________________________

(ii) State the synchronous speed of a three-phase 400V, 50Hz, four-poleinduction motor?

(1 mark)

________________________________________________________

________________________________________________________

(j) State TWO components that can be used as part of a circuit to filter arectifier output.

(2 marks)

(1) ________________________________________________________

(2) ________________________________________________________

(turn over)


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Question 2

Danger tags and out-of-service tags are used extensively in workplaces.

(a) Two registered electrical installers are carrying out electrical repairs on thesame refrigeration plant.

(i) State the main reason why danger tags are used.(2 marks)

________________________________________________________

________________________________________________________

________________________________________________________

________________________________________________________

________________________________________________________

________________________________________________________

(ii) State THREE actions to be taken when attaching danger tags to anisolating switch of the refrigeration plant.

(3 marks)

(1) ____________________________________________________

____________________________________________________

(2) ____________________________________________________

____________________________________________________

(3) ____________________________________________________

____________________________________________________

(turn over)


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(iii) State the TWO circumstances where the danger tags can beremoved.

(2 marks)

(1) ____________________________________________________

____________________________________________________

____________________________________________________

(2) ____________________________________________________

____________________________________________________

____________________________________________________

(b) Describe the circumstances where an out-of-service tag is used(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(c) You are doing a polarity test at the supply side of a three-phase main

switch to see if the switchboard is isolated.

Between which terminals would you test to clearly establish that isolation(or otherwise) has taken place.

(1 mark)

____________________________________________________________

____________________________________________________________

(turn over)


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Question 3

The method of installing cables in electrical installations depends on theenvironment in which the wires and cables are to be installed.

(a) TPS sheathed PVC cables are installed in an electrical installation, bothindoors and outdoors.

(i) State TWO reasons why some TPS sheathed cables would be installedin PVC conduit.

(2 marks)

(1) ____________________________________________________

____________________________________________________

(2) ____________________________________________________

____________________________________________________

(ii) State TWO design requirements to be considered when PVC conduit isused outdoors.

(1 mark)

(1) ____________________________________________________

(2) ____________________________________________________

(iii) State the requirement for installing extra-low voltage cables in thesame conduit and low voltage PVC cables.

(1 mark)

________________________________________________________

________________________________________________________

turn over)


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(b) Within the installation cables are installed in open cable ladders and opencable trays.

(i) Some cables carry large currents.

State the reason why is it necessary to securely fasten cables carryinghigh currents when installed in horizontal cable trays.

(2 marks)

________________________________________________________

________________________________________________________

________________________________________________________

(ii) What provision is made when telecommunication cables are installedin the same tray as low voltage cables?

(1 mark)

________________________________________________________

________________________________________________________

________________________________________________________

(iii) What provision is made where an open cable tray passes through thefire-rated wall of a switch room?

(1 mark)

________________________________________________________

________________________________________________________

________________________________________________________

(c) State the main effect on TPS sheathed cables that are installed throughwalls containing thermal insulation.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)


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Question 4

(a) The figures below are outlines of a three-phase RCD and a 5 pin socket.

Draw and label:

The internal circuit diagram of the three-phase RCD used for personalprotection that protects the 5-pin socket outlet.

The supply to the socket outlet The earthing arrangements

(5 marks)

(turn over)

Three-phasesocket outlet

Three-phase RCD


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(b) Describe the operation of an RCD when there is an active (phase) to earthfault that occurs on the circuit the RCD protects.

(4 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(c) State TWO types of electrical protection provided by a RCBO.(1 mark)

(1) ________________________________________________________

(2) ________________________________________________________

(turn over)


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Question 5

(a) The figure below shows a motor control circuit. On the diagram, make theappropriate wiring alterations to connect the remote stop-start and

emergency stop stations.(3 marks)

Note: Indicate the removal of any part of the circuit like this -

(b) A three-phase, 8 kW induction motor connected to a 400 V, 50 Hz, three-phase supply has a power factor of 0.81 and an efficiency of 84% whenfully loaded.

(i) Calculate the input power of the motor. (2 marks)

(turn over)

Remote start stopstation

Emergency stopstation

S1

Overloadcontacts

Stopbutton

Startbutton

M1

D1Timer

P N

M

S

D


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(ii) Calculate the input kVA of the motor.(2 marks)

(iii) Calculate the line current of the motor. (2 marks)

(c) State ONE reason why reduced-voltage starting of a large three-phaseinduction motor may be required.

(1 mark)

____________________________________________________________

____________________________________________________________

(turn over)


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Question 6

Introduction

The figure below represents a three-phase, star-connected 400V, 15 kWcommercial oven. The elements are of equal resistance.

(a) When the oven was installed, an earth loop impedance test showed a resultof 0.38. The resistance of the protective earthing conductor is 0.1

A high resistance joint of 7.9. has occurred in the protective earthingconductor.

A fault of 2 impedance has developed between L1 and the oven framewhile the oven is operating.

(i) Calculate the total current that will flow in L1 under the faultconditions.

(6 marks)

(turn over)

N

L1

L2

L3

Element 1

Element 2

Element 3

E


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(ii) Calculate the touch voltage that would appear on the frame of theoven

(2 marks)

(b) The oven is protected by 40A HRC fuses with a fusing factor (gG UtilisationCategory) of 1.5.

Use calculations to show why the HRC fuse did not operate when the faultoccurred

(1 marks)

(turn over)


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Question 7

Introduction

A new single-phase electric hot water cylinder is to be connected to an existingisolating switch in a small factory. The cylinder element is an MIMS type. A newflexible cord has been connected to the cylinder.

The old cylinder has been disconnected and removed.

(a) Two instrument tests need to be carried out to ensure that the hot-watercylinder is safe to connect to the electricity supply.

The only test instrument you have is a multi-function meter with insulationresistance (with 500V and 250V ranges), resistance, voltage andtemperature functions.

(7 marks)

Test 1

For this test:

Name the test. State the meter function selected. State the meter range selected. State how the test is carried out using the function and range

selected.

State an acceptable test result that permits the hot water cylinder tobe connected to the electricity supply.

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)


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Test 2

For this test:

Name the test. State the meter function selected State the meter range selected. State how the test is carried out using the function and range

selected. State an acceptable test result that permits the hot water cylinder to

be connected to the electricity supply.

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(b) The cylinder final subcircuit is supplied from a three-phase switchboard andis protected by an HRC fuse.

The isolating switch is not locked nor is it tagged.

Describe the procedure that needs to be followed to ensure personal safetybefore connecting the hot water cylinder to the isolating switch.

(3 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)


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Question 8

(a) Explain why rewireable fuses are classed as coarse excess current

protection.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(b) Explain why HRC fuses and MCBs are classed as close currentprotection.(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(c) HRC fuses provide short-circuit and overload protection to a three-phasemotor final subcircuit.

State the main reason why the HRC fuses do not provide overloadprotection for the motor.

(1 mark)

____________________________________________________________

____________________________________________________________

____________________________________________________________

(d) Apart from cost, state TWO technical advantages that HRC fuses havewhen compared to MCBs.

(1 mark)

(1) ________________________________________________________

(2) ________________________________________________________

(turn over)


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(e) Describe the term back-up protection in relation to the protection of finalsubcircuits.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(f) Describe the term discrimination in relation to electrical protection in anelectrical installation.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

____________________________________________________________

(turn over)


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Question 9

(a) Sketch and label a simple diagram to represent the neutral and earthingarrangements for an MEN distribution system showing:

A delta-star-connected 11 kV/400 V supply transformer showing theneutral line and earthing arrangements

A single-phase consumer switchboard that shows the neutral andearthing arrangement

A three-phase consumer switchboard that shows the neutral andearthing arrangement

(4 marks)

(b) State TWO factors that determine the prospective short-circuit current inan electrical installation.

(2 marks)

(1) ________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________

(turn over)


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(c) Briefly describe how earthing the metal frame of a Class I electricalappliance prevents electric shock hazards under fault conditions.

(2 marks)

____________________________________________________________

____________________________________________________________

____________________________________________________________

(d) An electrical installation has protective devices rated lower than the levelof prospective short-circuit current.

Describe TWO hazardous conditions that could occur in the installationwhen a high current fault occurs.

(2 marks)

(1) ________________________________________________________

________________________________________________________

(2) ________________________________________________________

________________________________________________________


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EIN03 QUESTIONS 19 NOVEMBER 2011

For Candidates Use For Examiners Use OnlyQuestionsAnswered

Marks

1

2

3

4

In the box, write thenumber of EXTRAsheets you haveused. Write NIL ifyou have not usedany

5

6

7

8

9

TOTAL

ein 03 questions 19 nov 2011

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