Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

An ohmmeter should never be connected to what type of circuit?

1. A live circuit

2. A low-resistance circuit

3. A circuit with multiple paths

4. A high-voltage circuit

The correct answer is: A live circuit

An ohmmeter is used to measure resistance in electrical components and circuits. It functions by sending a small current through the component and measuring the voltage drop, allowing the user to calculate resistance based on Ohm's Law. When measuring resistance, the circuit must be de-energized; otherwise, the presence of voltage can give misleading readings and potentially damage the ohmmeter. When connected to a live circuit, the voltages present can interfere with the ohmmeter's measurement process, leading to inaccurate resistance readings or possibly damaging the device. This is why using an ohmmeter on a live circuit is specifically cautioned against—safety and accuracy are at risk. Other scenarios, such as low-resistance circuits, circuits with multiple paths, or high-voltage circuits, may present their own challenges, but the critical factor when using an ohmmeter is that it should always be applied to de-energized systems to ensure reliable and safe operation.