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ET 36 - Electrician Theory Examination Marking Schedule Notes:1. (1 mark) means that the preceding statement/answer earns 1 mark. 2. This schedule sets out the accepted answers to the examination questions. A marker can exercise their discretion and decide on the overall accuracy of any answer that is presented in the candidate’s own words. 3. Symbols and terms - alternatives Power W or P Voltage V or E or U Phase Active Reference Question 1 Marking notes Marks (a) Any TWO of: (2 marks) An MEN switchboard: ● Has an MEN link between the neutral and earth busbars ● Has a connection to earth via an earthing lead to an earth electrode ● Is electrically closest to the point of supply ● Can supply to another MEN switchboard (b) They have a constant rotating magnetic field (2 marks) (c) Any TWO of: (2 marks) (d) (e) ● Reducing starting current ● Reducing voltage surges ● Limiting mechanical shock (i) 0.01 MΩ minimum (1 mark) (ii) 1Ω maximum (1 mark) Any TWO of: (2 marks) ● Capacity of the supply source ● Transformer impedance. ● Circuit impedance ● Length of cable route between the transformer and the main switchboard ET 36 ANSWERS – 11 SEPTEMBER 2010 1 Reference Question 1 Marking notes Marks (f) When current is flowing there is an internal volt drop due to the impedance of the windings. (g) (i) No effect (1 mark) (ii) Any ONE of (1 mark) (h) P ● 110 V ● 63.5V = V2 (2 marks) R = 240 x 240 24 P = 2400W = V2 (½ mark) R = 230 x 230 (½ mark) 24 (i) (j) = 2204.17W (½ mark) = 2400 – 2204.17 = 195.83 (½ mark) ● Under fault conditions the earthing of the metal frame keeps the frame of appliance at earth potential. (1 mark) ● This ensures the operation of protective devices (1 mark) (i) 1MΩ (1 mark) (ii) 5mA (1 mark) ET 36 ANSWERS – 11 SEPTEMBER 2010 2 Reference Question 2 Marking notes Marks (a) Each fitting has a 1 amp fuse, the circuit is protected by a 16A MCB. (1 mark) (b) (i) It protects the whole of the circuit. (1 mark) (ii) ● Short-circuit ● Overload. (c) (d) (i) It protects Fitting A (ii) ● Short-circuit ● Overload. (1 mark) (1 mark) (1 mark) (i) It protects the whole of the circuit. (1 mark) (ii) Any earth fault on the circuit. (1 mark) (e) The MCB (f) Any TWO of: (1 mark) (2 marks) ● The MCB would operate disconnecting all the lights in the circuit. ● The wiring and components in Fitting B may have a much lower current rating. ● The MCB may not trip and cause a shock hazard due to a faulty fitting. ET 36 ANSWERS – 11 SEPTEMBER 2010 3 Reference Question 3 Marking notes Marks (a) (b) (c) ● Use an ohmmeter. ● Test between the cable ends. resistance indicates a winding. A low (1 mark) ● Each winding must have the same resistance. (1 mark) ● Use an insulation resistance tester (½ mark) ● Use a test voltage of 500V d.c (½ mark) ● Test between windings. three (1 mark) ● Test between each of the three windings and the motor framework (1 mark) ● Each test result must be not less than 1 Megohm. (1 mark) each (1 mark) of the Any THREE of: (3 marks) ● Protective earthing continuity test. conductor ● Visual test. ● Polarity test. ● Check the integrity of the terminations ET 36 ANSWERS – 11 SEPTEMBER 2010 4 Reference Question 4 Marking notes Marks (a) (i) Ifault = 230 (½ mark) (7 + 0.5) = Itotal = = (ii) 30.66A (½ mark) Ifault + Iload = 30.66 + 25 (½ mark) 55.66A (1 mark) The 30A fuses have a fusing factor (gG Utilisation Category) of 1.5 Fusing current = 1.5 x 30 = 45 A (½ mark) Total current is 55.66A, which is more than the fusing current of 45A (½ mark) The fuse will operate. (b) (i) Ifault = (1 mark) 230 (½ mark) (7 + 12) = Itotal = = (ii) 12.1A (½ mark) Ifault + Iload = 12.1 + 25 (½ mark) 37.1A (1 mark) Total current is 37.1A, which is less than the fusing current of 45A (½ mark) The fuse will not operate (½ mark) or The fuse may take a long time to operate. (iii) Vd across Earth conductor equals shock voltage VdE = IxR = 12.1 x 12 = 145.2 V (½ mark) (½ mark) Electric shock hazard of 145.2V frame to earth exists (1 mark) ET 36 ANSWERS – 11 SEPTEMBER 2010 5 Reference Question 5 Marking notes Marks (a) Red line L1 L2 White line L3 Blue line Neutral bar Earth Bar C D B A Socket-outlet E Earth fault Class 1 heater (b) ● Accurate fault loop drawn (2 marks) (i) Between points A and B (1 mark) (ii) Between points C and D (1 mark) (iii) Between points D and E (1 mark) ET 36 ANSWERS – 11 SEPTEMBER 2010 6 Reference Question 5 Marking notes Marks (c) Iload = W (½ mark) V = 2000 (½ mark) 230 IF = 8.7 A = 230 (1 mark) (½ mark) (0.5 + 0.67 + 60) IT = 3.76A (1 mark) = IL + IF (½ mark) = 8.7 + 3.76 = 12.46A (1 mark) ET 36 ANSWERS – 11 SEPTEMBER 2010 7 Reference Question 6 Marking notes Marks (a) (b) ● Polarity ● Earth Continuity ● Earth Loop Impedance ● RCD Test (i) Any ONE of: (ii) (2 marks) ● Earth loop impedance test ● RCD test ● Polarity test (1 mark) The question is not specific enough to indicate which of the tests should be carried out. Any ONE of the following tests: Earth Loop Impedance This test has to show ● Use of an earth loop impedance tester (1 mark) ● Testing between the active conductor and the protective earthing conductor on the socket out let (1 mark) ● Impedance low enough to operate protection (1 mark) RCD Test This test has to show ● Use of RCD tester ● Plugging outlet ● RCD should operate within 300 mS at the maximum residual current of 30 mA. test into the socket Polarity Test This test has to show (c) (i) ● Use of voltage tester ● Testing between active and neutral; active and earth; and neutral and earth on the socket outlet ● Values of 230V between active and neutral and active and earth. 0V between neutral and earth. Any ONE of: ● Earth Continuity (1 mark) The question is specific enough ET 36 ANSWERS – 11 SEPTEMBER 2010 not to 8 Reference Question 6 Marking notes Marks ● (ii) indicate which of the tests should be carried out. Polarity Any One of the following tests: Earth continuity This test has to show: ● Use of an ohmmeter ● Testing between the earth contact on the plug and the switchboard earth bar ● A reading low enough to operate the protective device. Polarity (1 mark) (1 mark) (1 mark) This test has to show: ● ● ● Use of an ohmmeter The phase conductor being switched The neutral and earth conductors going to the correct terminals ET 36 ANSWERS – 11 SEPTEMBER 2010 9 Reference Question 7 Marking notes Marks (a) Fuse Start Stop O/L P Coil Hold-in contact P Fuse ● Correctly connected 400V supply ● Correctly connected start button ● Correctly connected stop button (1 mark) If a 230V working circuit shown award (½ mark) is 2½marks (½ mark) ● Correctly connected hold-in contact (½ mark) ● Correctly connected coil (½ mark) ● Correctly connected thermal overload (½ mark) ● 400V working circuit (1½ marks) (b) Remote start/stop station 3 core cable The cable is connected so that: (c) ● The remote stop is in series with the local stop button (1 mark) ● The remote start in parallel with the local start button (1 mark) ● Working circuit (1 mark) The stop parallel. buttons have been wired in (2 marks) ET 36 ANSWERS – 11 SEPTEMBER 2010 10 Reference Question 8 Marking notes Marks (a) E N L Tripping Device Test button Sensing coil/toroid Class I equipment load ● Correctly connected test circuit and resistance (1 mark) Hazardous conditions ● (1 mark) ● ● Correctly connected sensing coil/toroid ● Correctly connected phase, neutral and earth. (1 mark) ● Correctly connected tripping circuit (1 mark) ● ● ● ● (b) It has to be tested to ensure that it is voltage-dependent (that is, it will not automatically reset if supply is restored.) (2 marks) (c) Yes (½ mark) The RCD detects the imbalance regardless of A short circuit No test resistance in the test circuit. The socket outlet is not earthed The active of the test button circuit is connected to the supply side of the main contacts The neutral is not switched No neutral conductor shown (½ mark) ET 36 ANSWERS – 11 SEPTEMBER 2010 11 Reference Question 8 Marking notes Marks the polarity of the supply. (d) PRCD Portable Residual Current Device. (1 mark) RCBO Residual Circuit Breaker Overcurrent protection (1 mark) SRCD Socket Residual Current Device with (1 mark) ET 36 ANSWERS – 11 SEPTEMBER 2010 12 Reference Question 9 Marking notes Marks (a) (i) Hazardous condition: ● The star point not earthed L1 L2 L3 (ii) ● Correct delta connections (½ mark) ● Correct star connections (½ mark) ● Star point earthed (½ mark) Secondary phase voltage = 11000 (½ mark) 43.3 = 254 V (1 mark) (iii) Secondary line voltage = 254 x √3 (½ mark) = 440 Volts (1 mark) (iv) Primary line current = kVA x 1000 (½ mark) √3 x VL = 150000 (½ mark) √3 x 11000 = (v) 7.87 A (1 mark) Secondary line current = 150000 (½ mark) √3 x 440 = (b) 196.83 A (1 mark) Any ONE of: (2 marks) ● The iron core is laminated. ● Special types of alloys are used for the core ET 36 ANSWERS – 11 SEPTEMBER 2010 13