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Q1— Section header —
1.1State TWO main types of washing machines (2\
1.2As maintenance electrician you are called out to replace the immersion element of water heater as shown in the
Q2— Section header —
2.1Indicate whether the following statements are TRUE or FALSE by writing only 'True' or 'False' next to the question number (2.1.1
2.1.6\in the ANSWER BOOK.
2.1.1Steel conduit pipes shall be earthed.
2.1.2A h air dryer does not need to be earthed.
2.1.3A r efrigerator does not need to be earthed.
2.1.4Hot water and cold water systems shall be bonded together and earthed.
2.1.5Conducti ve parts of discharge light fittings shall be earthed.
2.1.6Fixing such as cleats, clips, saddles and clamps shall be earthed. (6 1\ (6\
2.2Briefly explain the difference between an earthing conductor and an earth electrode as applicable to electrical installations. (4\ [10] 1104126310
Q3— Section header —
3.1Draw a neat , labelled circuit diagram of a high pressure mercury vapour discharge lamp
3.2State TWO applications of each of the following lamps
3.2.1Sodium vapour discharge lamps.
3.2.2Cold cathode neon lamps (2 2\ (4\ [10]10
Q4— Section header —
4.1A sine wave has a maximum value of 311 V and a time period of 20 ms.
4.1.1Write down the equation that describes this waveform. (3\
4.1.2Calculate the effective value of this waveform. (2\
4.2A sine wave has an rms value of 240 V and a frequency of 50 Hz.
4.2.1Write down the equation that describes this waveform. (3\
4.2.2Calculate the average value of this waveform. (2\ [10]10
Q5— Section header —
5.1The impedance of the circuit (6\
5.2The current following through the circuit (2\
5.3The phase angle (2\ [10] 1104126310
Q6— Section header —
6.1Draw a neat fully labelled sketch to show the waveforms of a three phase supply. (3\
6.2Draw a phasor diagram represent the waveforms drawn in
Q6— Section header —
6.3The stator windings of a three phase induction motor are connected in star. If this motor is connected to a 380 V supply, it draws a current of 4 A from the supply at a power factor of 0,89
6.3.1he voltage across each winding (2\
6.3.2he phase current of the motor (1\
6.3.3he input power to the motor in (3\ [10]10
Q7— Section header —
7.1How can you determine the turns ratio of a transformer if it is not possible to count the number of turns on the windings? (2\
7.2three phase step down transformer has a delta connected primary and star connected secondary. The primary line voltage is 6,6
7.2.1he secondary phase voltage (2\
7.2.2he transformation ratio (2\
7.2.3he primary line current when the secondary line current is 500 A (4\ [10]10
Q8— Section header —
8.1Name any TWO tests that are conducted on a DC machine. (2\
8.2State TWO advantages that DC motors have over AC motors. (2\
8.3Draw the oad characteristic of compound wound motor s clearly showing the
8.4State ONE application of a series motor. (1\ [10] 1104126310
Q9— Section header —
9.1State the purpose of the rotor of an induction motor. (2\
9.2Determine the approximate speed of a four pole induction motor that is connected to 380 , 50
9.3Draw a neat and fully label ed circuit diagram of a manual
Q10— Section header —
10.1Name t wo types of moving iron instruments (2\
10.2Draw a neat, labelled sketch of a full wave rectifier using four diodes (4\
10.3Give the definition for each of the following terms:
10.3.1Conventional current flow
10.3.2Ion (2 1\ (2\
10.4State TWO materials used in the manufactur e of semiconductor devices. (2\ [10] TOTAL: 10010