Tools and Measuring Instruments
This domain tests hand tools, testers and instruments used to install, test and diagnose electrical circuits. The exam expects safe use of screwdrivers, pliers, wire strippers, insulation testers, multimeters, clamp meters and energy meters, plus correct connection of meters to a circuit.
Core rules
- A voltmeter is connected in parallel with the load. An ammeter is connected in series. A clamp meter measures current by surrounding one conductor only.
- A multimeter's voltage range is used to check supply; its resistance range must be used only on a dead circuit.
- An insulation tester (megger) applies a high DC test voltage, commonly 500 V for low-voltage installations, and displays resistance in MΩ. Good insulation is typically at least 1 MΩ for a low-voltage circuit.
- Continuity testing confirms a low-resistance path. A blown fuse, open switch or broken wire shows continuity failure.
- An energy meter measures kWh, not kW. The connected load and time both affect the reading.
Worked example
A 500 V insulation test on a 230 V circuit gives 0.5 MΩ. The leakage current at 230 V would be I = V/R = 230/500,000 = 0.00046 A, or 0.46 mA. Although small, the reading is below the 1 MΩ acceptance guide, so the circuit should be investigated before energising.
Traps
Do not measure voltage with the meter set to current or resistance. Do not test insulation on a live circuit. Do not clamp two conductors together and expect a useful reading. Do not treat a low-voltage continuity beep as an insulation test.