Tools and Measuring Instruments
What the domain tests
Tools and Measuring Instruments tests safe selection and correct connection of hand tools and meters: screwdrivers, pliers, crimpers, test lamps, multimeters, meggers, clamp meters and earth testers.
Core rules
- Use insulated hand tools for electrical work and check insulation before use.
- A voltmeter is connected in parallel; an ammeter in series. A clamp meter measures current without breaking the circuit by sensing the magnetic field around a conductor.
- A multimeter selects function and range before probing; start on a higher range if unsure.
- A megger measures insulation resistance with the circuit dead and isolated. For a low-voltage motor, a 500 V megger is typical; a very low reading indicates moisture or damaged insulation and must be investigated.
- An earth tester measures earth-electrode resistance; a test lamp proves dead only if it is known to work.
Worked example
You need the running current of a 230 V pump without stopping it. Connect a clamp meter around one live conductor only, set to AC amperes, and read the value. If you clamp the whole cable containing live and neutral, the magnetic fields cancel and the reading is near zero. That reasoning-one conductor, correct function-is what earns the mark.
Traps
Never connect an ammeter in parallel across a supply; it has very low resistance and can short the circuit. Never use a megger on a live circuit. Do not use a multimeter’s continuity range to prove a circuit dead. Do not clamp a two-core cable and trust the current reading.