What is the best tester to use for testing conductor insulation near operating voltage levels?

The best tester for evaluating conductor insulation near operating voltage levels is the megohmmeter. This device is specifically designed to measure high insulation resistance by applying a high voltage to the conductor. By doing so, it provides an accurate reading of the insulation's integrity, which is critical for ensuring safety and performance in electrical systems.

Using a megohmmeter can help identify insulation degradation, which can result from environmental factors, aging, or physical damage. Given that regular operational voltages are relatively low compared to the high voltages used by megohmmeters, this device can stress the insulation sufficiently to reveal weaknesses without being harmful to the system being tested.

Other testing options, such as a low-resistance ohmmeter, are more suited for measuring resistance rather than insulation quality, while a digital multimeter is generally limited to low voltage measurements and does not provide the necessary level of testing for insulation. A high-voltage tester, although capable of providing information about insulation, may not be as safe or effective for routine insulation resistance testing as the megohmmeter. Thus, the megohmmeter stands out as the most appropriate choice for this specific testing scenario.