Electrical Test Instruments PDF

Learning Outcomes Explain the purpose of test instruments in electrical work (continuity tester, multimeter, insulation resistance tester) Explain the functions of a socket outlet polarity tester Explain the method to test for the correct polarity of a socket outlet 1.9.1 In...

Learning Outcomes Explain the purpose of test instruments in electrical work (continuity tester, multimeter, insulation resistance tester) Explain the functions of a socket outlet polarity tester Explain the method to test for the correct polarity of a socket outlet 1.9.1 Introduction Electrical personnel use many different types of test instruments. These instruments are used to determine whether a circuit is correctly wired, sound or faulty. Some common instruments are the continuity tester, the multimeter, the socket outlet polarity tester and the insulation resistance tester. 1.9.2 Continuity Tester A continuity tester can be used to check the electrical continuity of an electric circuit, measure its resistance and check the condition of the fuses. The instrument carries its own batteries, giving it an independent power supply. Fig. 1.9-1: Continuity tester Before taking a reading, ensure that: the circuit to be measured or tested is not connected in parallel with another circuit; and the circuit to be measured is not live. Unit 1.9 | Electrical Test Instruments 62  1.9.3 Multimeter A multimeter can measure many types of electrical quantities, such as: current; voltage; and resistance. A multimeter that is set to measure resistance (Fig. 1.9-2) is basically a continuity tester. Fig. 1.9-2: Measuring resistance When using a multimeter to check the continuity of a circuit, ensure that the circuit is not energised or live. 1.9.4 Socket Outlet Polarity Tester Fig. 1.9-3: Checking a socket outlet connection Fig. 1.9-3 shows a 13A socket outlet polarity tester. It has three lights to indicate whether the outlet voltage or outlet wiring connection is correct. Examples of wrong wiring connections are open earth, open neutral, open live, reversed live and earth, or reversed live and neutral wires. Unit 1.9 | Electrical Test Instruments 63  1.9.5 Insulation Resistance Tester Fig. 1.9-4: Digital insulation tester Fig. 1.9-5: Analogue insulation tester Fig. 1.9-6: Measurement with insulation resistance tester An insulation resistance tester is used to measure very high values of resistance (Figs. 1.9-4 and 1.9-5). It is also used to check the conditions of circuit cables and motor winding by measuring the resistance of their insulation (Fig. 1.9-6). It measures resistance in mega-ohms (MΩ). NOTE: One mega-ohm is equal to one million ohms. As with using a continuity tester, ensure that the circuit is not energised when using an insulation resistance tester. Unit 1.9 | Electrical Test Instruments 64