Why should resistance measurements always be made with the system power shut off?

Resistance measurements should always be made with the system power shut off because it is essential to ensure accurate measurements. When the power is on, electrical interference can alter the readings due to the presence of voltage, causing the ohmmeter to register a value that does not accurately reflect the actual resistance of the circuit or component. This interference can lead to misleading results and ultimately complicate troubleshooting or repairs.

In addition to accuracy, shutting off the power is also crucial for safety, as it reduces the risk of electric shock to the technician performing the measurement. While compliance with safety regulations is important, the primary reason for turning off the power during resistance measurements is to prevent inaccuracies caused by live electrical interference. Thus, ensuring that the measurements reflect the true conditions of the circuit without any external electric influence is critical.