When measuring resistance with an ohmmeter, what must be done prior to measuring?

Before measuring resistance with an ohmmeter, it is essential to disconnect power to the circuit or the component being tested. This is necessary to ensure both accurate readings and safety. An energized circuit can provide misleading resistance readings because the presence of voltage affects the resistance measured by the ohmmeter.

When power is on, it can create a current flow that interferes with the measurement process, potentially damaging the meter or leading to unsafe conditions such as electric shock. Disconnecting the power removes this risk and allows the meter to accurately determine the resistance in ohms without interference.

In addition, while it is vital to maintain safety and accuracy, options such as calibrating the meter or checking for shorts are important steps in general maintenance or troubleshooting but are not required specifically prior to measuring resistance.