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EIN 10
Candidate Code No.
For Board Use Only
Result Date Int
Result Date Int
ELECTRICAL INSTALLER THEORY
EXAMINATION
20 June 2015
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. Non-programmable calculators may be used. 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.
(turn over)
Question 1 (a) Explain why mechanical interlocks are incorporated in a star/delta
starter. (2 marks)
____________________________________________________________
____________________________________________________________
____________________________________________________________
(b) (i) State the reason why a capacitor would be connected in series with
the start winding in a single-phase a.c. split-phase induction motor. (1 mark)
________________________________________________________
________________________________________________________ (ii) For what reason would you connect a resistor across a circuit after
the electricity supply to that circuit has been isolated. (1 mark)
________________________________________________________
________________________________________________________ (c) (i) State the main consideration when selecting a protective device for a
switchboard. (1 mark)
________________________________________________________
________________________________________________________ (ii) A residual current device (RCD) that protects a final subcircuit and a
fixed-wired Class I electrical appliance has operated. What has the RCD detected that would cause it to operate?
(1 mark)
________________________________________________________
________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 2
Question 1 continued (d) In relation to HRC fuses: (i) Define the term cut off characteristic as it applies to HRC fuses.
(1 mark) ________________________________________________________ ________________________________________________________ (ii) Define the term current rating as it applies to HRC fuses.
(1 mark) ________________________________________________________ ________________________________________________________ (e) State ONE reason why the neutral in the MEN system is multiple-earthed.
(2 marks) ____________________________________________________________
____________________________________________________________ ____________________________________________________________ (f) An electrical installer used a voltmeter 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 installer proceeded to dismantle the isolator and received an electric
shock. State ONE reason why the person received the shock. (2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 3
Question 1 continued (g) (i) A three-phase motor has: Six terminals on the terminal block A six-core and earth flexible cable is connected to the terminal
block. To what type of motor starter would the three-phase motor be
connected? (1 mark)
________________________________________________________
(ii) A three-phase motor has: Six terminals on the terminal block A three-core and earth flexible cable is connected to the
terminal block. To what type of motor starter would the three-phase motor be
connected? (1 mark)
________________________________________________________ (h) (i) What device is used to provide starting torque in a shaded pole motor?
(1 mark) ________________________________________________________ (ii) State TWO applications for a shaded-pole motor.
(1 mark) (1) ____________________________________________________ (2) ____________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 4
Question 1 continued (i) A star-connected squirrel cage motor that has been operating normally
develops a fault. The tests on the 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) ____________________________________________________________
____________________________________________________________
(j) One reason the metal frame of a Class I electrical appliance is earthed is to ensure the operation of a protective device under fault conditions.
State ONE other reason why the metal frame of a Class I electrical
appliance is earthed. (2 marks)
____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 5
Question 2 (a) State the TWO reasons why the prove-test-prove method is used for taking
voltage tests for the purpose of isolation. (2 marks)
(1) ________________________________________________________
________________________________________________________ ________________________________________________________ (2) ________________________________________________________
________________________________________________________ ________________________________________________________ (b) (i) Define the term switching off as it relates to three-phase equipment.
(1 mark) ________________________________________________________ ________________________________________________________ (ii) Define the term isolation as it relates to three-phase equipment.
(2 marks)
________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________ ________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 6
Question 2 continued (c) A three-phase, 10 kW pump motor has been isolated and the motor cables
have been disconnected from the motor. The motor cables are still connected to the DOL starter.
State TWO precautions which must be taken to ensure the safety of
persons and property before you leave the work site. (2 marks)
(1) ________________________________________________________
________________________________________________________ ________________________________________________________ (2) ________________________________________________________
________________________________________________________ ________________________________________________________ (d) A three-phase fixed-wired machine is protected by MCBs. The machine has
been isolated from the supply and is being repaired. The repair will take some time.
Describe THREE different methods of ensuring the machine remains
isolated. (3 marks)
(1) ________________________________________________________
________________________________________________________ ________________________________________________________ (2) ________________________________________________________
________________________________________________________ ________________________________________________________ (3) ________________________________________________________
________________________________________________________ ________________________________________________________
(turn over) EIN10-QUESTIONS – 20 JUNE 2015 7
Question 3 (a) (i) State the permitted maximum residual current rating of an RCD used
for personal protection in a domestic electrical installation. (1 mark)
________________________________________________________ (ii) State the permitted maximum residual current rating of an RCD used
for personal protection in a child-care centre. (1 mark)
________________________________________________________ (iii) State the permitted maximum residual current rating of an RCD used
for the protection of property. (1 mark)
________________________________________________________ (b) An RCD rated for personal protection is a safeguard designed to operate if
earth leakage current flows through a person’s body to earth. State why that person does not receive a severe shock from the earth
leakage current? (2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 8
Question 3 continued (c) A Residual Current Circuit Breaker (RCCB) is installed in a single phase
circuit. Explain why the RCCB does not operate when there is a short circuit
between active (phase) and neutral in the single phase circuit? (2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________ (d) Explain why a PRCD is required to be voltage dependent.
(2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________ (e) The phase and neutral on the supply side of a single phase RCD have been
transposed. Would the RCD operate if it detected an earth leakage fault on the circuit it
protects? State a reason to support your answer. (1 mark)
____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 9
Question 4 Introduction Another electrical installer has isolated, disconnected and repaired a 400V three-phase circular saw in a joinery factory. You are required to: Reconnect the machine by connecting the flexible cord to the DOL (direct-
on-line) starter mounted on an adjacent pillar, and Recommission the circular saw There are no danger tags or lock attached to the isolator controlling the DOL starter. The isolator has a locking facility. The only test instrument available is a multi-function test instrument. Use the information in the introduction to this question to answer parts 4(a), 4(b), 4(c) and 4(d). (a) State the TWO instrument tests that need to be carried out on the circular
saw to ensure it is safe to connect to the supply. (1 mark)
Test No. 1 ________________________________________________
Test No. 2 ________________________________________________ (b) For Test No. 1 stated in (a) State the range selected on the test instrument State the function selected on the test instrument State the test voltage (if applicable) Describe how the test is carried out with the function and range
selected. State the permitted test result that allows the saw to be returned to
service. (3 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________
____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 10
Question 4 continued (c) For Test No. 2 stated in (a) State the range selected on the test instrument State the function selected on the test instrument State the test voltage (if applicable) Describe how the test is carried out with the function and range
selected. State the permitted test result that allows the saw to be returned to
service. (3 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________
____________________________________________________________ (d) The saw has been connected to the DOL starter but not livened. A test needs to be carried out to ensure that the saw’s protective devices
will operate under fault conditions. For this test: State the function selected on the test instrument State the range selected on the test instrument Describe how the test is carried out with the function and range
selected. The permitted test result that allows the saw to be returned to service.
(3 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________ ____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 11
Question 5 (a) A factory is supplied by a 150 kVA three phase, delta-star connected
transformer with a turns ratio of 47.8 to 1. The primary is connected to an 11kV three phase supply and the transformer is fully loaded.
(i) Calculate the secondary phase voltage.
(2 marks) (ii) Calculate the secondary line voltage.
(2 marks) (iii) Calculate the primary line current.
(2 marks)
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 12
Question 5 continued (iv) Calculate the secondary line current.
(2 marks) (b) How is the output of a transformer rated?
(1 mark)
____________________________________________________________ (c) State TWO typical winding configurations found in transformers.
(1 mark)
(1) ________________________________________________________
(2) ________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 13
Question 6 Introduction The figure below represents a 400V, three-phase commercial oven comprising three 6 kW single-phase elements. Each phase is protected by a 32A HRC fuse with a fusing factor (gG Utilisation Category) of 1.5.
An earth fault of 6Ω has developed between L1 and the oven frame while the oven is operating. The fault occurred at point X. The earth fault loop impedance is 0.38Ω. Use the information in the introduction to this question to answer parts 6(a), 6(b) and 6(c)
(turn over)
X N
L1
L2
L3
Element 1
Element 2
Element 3
E
EIN10-QUESTIONS – 20 JUNE 2015 14
Question 6 continued (a) Calculate the total current that will flow in L1 under the fault conditions.
(6½ marks)
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 15
Question 6 continued (b) Refer to the following graph and determine how long it with take the 32A
HRC fuse to operate with the fault current flowing. (1 mark)
____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 16
Question 6 continued (c) The protective earthing conductor resistance is 0.28Ω. Use calculations to determine whether any touch voltage hazard exists to
the operator of the oven. (2½ marks)
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 17
Question 7 (a) Explain why rewireable fuses are classed as coarse excess current
protection. (2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________ ____________________________________________________________ (b) Explain why Gg type HRC fuses and MCBs are classed as close current
protection. (2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
____________________________________________________________ ____________________________________________________________ (c) HRC fuses and thermal overloads provide protection for a final subcircuit
and motor. State the main reason why the HRC fuses are not expected to provide
overload protection for the motor. (1 mark)
____________________________________________________________
____________________________________________________________ ____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 18
Question 7 continued (d) Apart from cost, state TWO technical advantages that HRC fuses have
when compared to MCBs. (1 mark)
(1) ________________________________________________________ (2) ________________________________________________________ (e) An MCB provides protection for a final subcircuit. State the main reason
why HRC fuses are installed as back-up protection on the same final subcircuit.
(2 marks) ____________________________________________________________
____________________________________________________________ ____________________________________________________________ ____________________________________________________________ (f) Explain how correct discrimination between protective devices occurs in
an electrical installation. (2 marks)
____________________________________________________________
____________________________________________________________ ____________________________________________________________ ____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 19
Question 8 (a) The figure below represents the components of the power circuit of a DOL
forward and reverse starter. The components are: The three-phase supply The forward contactor contacts The reverse contactor contacts The thermal overloads The motor On the figure draw the conductors so the motor can be operated in the
forward and reverse directions. Overload protection for the motor must operate in either direction.
(5 marks)
(turn over)
L1 L2 L3
M
W
V
U
Forward contactor
Reverse contactor
EIN10-QUESTIONS – 20 JUNE 2015 20
Question 8 continued (b) A 400V, three-phase motor is started with a DOL (direct-on-line) starter.
When started, the motor draws 90A and produces 200% full-load torque. (i) Calculate the starting current if the same motor is started with a
star/delta starter. (2 marks)
(ii) Calculate the percentage (%) of starting torque if the same motor is
started with an auto-transformer starter with an 80% tap. (2 marks)
(c) Explain the term ramp time as it relates to an a.c. variable speed
controller. (1 mark)
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 21
Question 9 (a) When carrying out testing on a low voltage electrical installation, which
document details the tests and checks required to be carried out? (1 mark)
____________________________________________________________ (b) The two figures below represent the front view of two single-phase socket
outlets. Label the polarity of the socket outlet connections on the figures.
(3 marks)
IEC 60309AS/NZS 3112
Note: You must show the polarity completely correct to gain
marks.
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 22
Question 9 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 you would expect to find with the switch OFF: Between Active – Neutral ________________________________
Between Active – Earth ________________________________
Between Neutral – Earth ________________________________ (ii) What voltage you would 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
State TWO reasons why you would get these readings? Note: The voltage tester is operating correctly.
(2 mark)
(1) ________________________________________________________ ________________________________________________________ (2) ________________________________________________________ ________________________________________________________
(turn over)
EIN10-QUESTIONS – 20 JUNE 2015 23
Question 9 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
State the reason why you would get these readings. Note: The voltage tester is operating correctly.
(1 mark)
____________________________________________________________ ____________________________________________________________
EIN10-QUESTIONS – 20 JUNE 2015 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
1
2
3
4
5
6
7
8
9
TOTAL
EIN10-QUESTIONS – 20 JUNE 2015 25