Final answer:
To verify a de-energized circuit, a Multimeter, Voltmeter, and Phase tester are used. A Multimeter measures various electrical properties, a Voltmeter measures potential differences in parallel, and a Phase tester detects voltage presence.
Step-by-step explanation:
The three test instruments that can be used to verify that no voltage is present in a de-energized circuit before beginning work are a Multimeter, Voltmeter, and Phase tester. A multimeter is a versatile tool that can measure voltage, current, and resistance; hence, it can be used to ensure there is no voltage in a circuit. A voltmeter measures the potential difference between two points in a circuit and must be connected in parallel across the points to be tested. Finally, a phase tester, also known as a voltage tester, can detect the presence of voltage in a circuit element.
When it comes to measuring voltage, it is crucial to connect the voltmeter correctly. Placing a voltmeter in series with a component would not provide a correct measurement of the voltage because voltmeters are designed to be connected in parallel to measure the potential difference accurately. This ensures they receive the full voltage and have a minimal effect on the circuit. An ohmmeter operates based on Ohm's law, measuring resistance by applying a small voltage to the circuit and measuring the resulting current, then calculating the resistance value.