NATIONAL CERTIFICATE (VOCATIONAL) ELECTRICAL WORKMANSHIP NQF LEVEL 3 NOVEMBER 2009

Transcription

1 NATIONAL CERTIFICATE (VOCATIONAL) ELECTRICAL WORKMANSHIP NQF LEVEL 3 NOVEMBER 2009 ( ) 3 November (X-Paper) 09:00 12:00 This question paper consists of 5 pages.

2 ( ) -2- NC740(E)(N3)V TIME: 3 HOURS MARKS: 100 INSTRUCTIONS AND INFORMATION Answer ALL the questions. Read ALL the questions carefully. Number the answers according to the numbering system used in this question paper. ALL work you do not want to be marked must be clearly crossed out. Write neatly and legibly.

3 ( ) -3- NC740(E)(N3)V QUESTION 1: TRADE PRACTICES A task list forms a very important part in the planning of any task. State THREE activities that are included in the planning for the task to be completed effectively. The employees at Telkom decided not to follow the safety requirements as stipulated by the Occupational Health and Safety Act. Name TWO consequences of this behaviour. Working environments are characterised by rules and procedures in order to ensure that the site is safe. Peter is a new employee who did not receive proper induction about the safety of machinery and equipment. As a result he failed to follow the safety rules and procedures when carrying out his day- today duties. List and explain THREE consequences of Peter not following safety rules and procedures. A technician can use combination pliers for different purposes. State THREE different parts of combination pliers that allows it to be used for more than one purpose. A consumer telephoned and asked you to come and fix a problem involving a household installation. She indicated that some of the lights were tripping the circuit breaker and that when the circuit breaker was 'on', two of the lights did not work. You will need measuring instruments and safety equipment to carry out the work. Which THREE pieces of safety equipment do you require in order to carry out this work? QUESTION 2: TESTING AND MEASURING EQUIPMENT 2.1 State the functions of each of the following measuring instruments: Tong-tester Stroboscope tachometer 2.2 Name THREE tests that the megger can be used for. 2.3 Analogue meters must be zeroed before they are used. Explain, in your own words, how to zero an ohmmeter.

4 ( ) -4- NC740(E)(N3)V Draw a labelled circuit diagram consisting of the battery, switch, voltmeter, ammeter and a resistor. Name TWO differences between an analogue and a digital meter. QUESTION 3: FAULT-FINDING AND TESTING 3.1 State SIX safety precautions that need to be considered when working on live electrical circuits or equipment. 3.2 You are given a kettle to do fault-finding and testing. Name SIX steps to be followed when diagnosing the problem. 3.3 You have to do a quality control check after a meter has been installed. What are you going to use to ensure that the meter has been installed correctly? 3.4 The technical specifications of the gate automation machine are given below. TECHNICAL DATA UNITS SPECIFICATIONS Motor 220 V single phase Gearbox Oil-filled worm drive Electricity consumption ±2,8 A Rated frequency 50 Hz Motor power 380 W Motor protection Thermal load Duty cycle 65% Gate speed 12 metres per minute Torque ±50 N.m Maximum gate weight 600 kg Independent in both directions, each Limit switches with a double action for additional reliability. Mechanical adjustable obstruction Obstruction sensing in both directions. Can accommodate I/R beams sensors. Weight ±23 kg (include rack and base) Read the above information carefully and answer the questions that follow What is the operating voltage of the motor? Name the THREE safety devices used for the protection of the motor. (1) What is the rated electrical current consumption and the input power of the motor?

5 ( ) -5- NC740(E)(N3)V QUESTION 4: REPAIR AND MAINTENANCE 4.1 What is maintenance? (Explain in your own words.) 4.2 At regular intervals, companies have a maintenance schedule for maintaining power tools and appliances. Draw up a maintenance plan showing SIX steps that can be followed to regularly check the tools and appliances. 4.3 It is always important to maintain domestic appliances and if this process is not done step by step, the maintenance will not be done properly. The statements below may be FALSE or TRUE in terms of the maintenance process. Indicate whether the following statements are TRUE or FALSE. Write only 'true' or 'false' next to the question number ( ) in the ANSWER BOOK It is not necessary to read the manufacturer's manual. Do visual inspection. Test run the appliance. Test earth continuity and insulation resistance. You must not loosen the cover of the terminal box. Maintain the appliance without dismantling it. 4.4 Explain the following terms using your own words: Visual inspection Test run Dismantle (3 2) QUESTION 5: INSTALLATIONS 5.1 You are required to work on a machine that has been disconnected from all sources of electricity but which is liable to be activated or to retain an electrical charge. What precautionary measures must be place in order to prevent danger in case the machine is energised or made alive while you are working on it? (4) 5.2 The circuits of an AC motor starter are split into two circuits. Name the TWO circuits and briefly explain the differences between these circuits. (8) 5.3 Name and explain FOUR procedures of commissioning a small single-phase AC machine and control gear before it is handed over to the company. (8) TOTAL: 100