An ohmmeter can be connected to a live circuit.

An ohmmeter can be connected to a live circuit.

• A. False
• B. True
• C. Only with supervision
• D. Depends on meter type

Answer: (A)

Measuring resistance with an ohmmeter relies on the meter injecting a small test current from its own internal battery and reading the resulting voltage drop. If the circuit is energized, that external voltage and current interfere with the meter’s test signal, leading to inaccurate readings and potentially driving current through parts of the circuit or the meter that could cause damage or a safety hazard. For reliable, safe resistance measurements, the circuit must be de-energized and the part being tested isolated (discharging any capacitors as needed). The idea that it could be done safely or without removing power isn’t correct, and supervision or the type of meter doesn’t change this fundamental safety rule.

Measuring resistance with an ohmmeter relies on the meter injecting a small test current from its own internal battery and reading the resulting voltage drop. If the circuit is energized, that external voltage and current interfere with the meter’s test signal, leading to inaccurate readings and potentially driving current through parts of the circuit or the meter that could cause damage or a safety hazard. For reliable, safe resistance measurements, the circuit must be de-energized and the part being tested isolated (discharging any capacitors as needed). The idea that it could be done safely or without removing power isn’t correct, and supervision or the type of meter doesn’t change this fundamental safety rule.