How should insulation resistance on a cable be checked?

To properly assess the insulation resistance of a cable, it is essential to isolate both ends of the cable. This step is crucial because it ensures that there are no parallel paths for current to flow, which can give misleading results. Isolating both ends means disconnecting the cable from any circuits, devices, or equipment that could influence the readings. By doing so, you can accurately measure the insulation resistance without interference, providing a valid indication of the cable's insulation integrity.

Furthermore, it is important to apply a standardized testing voltage, generally between 250V to 1000V, depending on the insulation type and application, to assess the insulation's performance effectively. This method allows for consistent and reliable readings that reflect the true condition of the insulation material.

In contrast, testing only one end does not account for any connections that may exist at the other end, while connecting to a ground source could lead to grounded paths that short-circuit the resistance measurement. Checking the voltage level provides information about the operational status of the circuit rather than the integrity of the cable insulation. Hence, isolating both ends provides a thorough and accurate evaluation of insulation resistance.