What type of device is used to measure the resistance or breakdown strength of conductor insulation?

Answer: B — Megohmmeter

The megohmmeter is designed specifically to measure the insulation resistance of electrical conductors by applying a high voltage to the insulation material. This is crucial for ensuring that the insulation is intact and capable of withstanding the electrical stress it will encounter in service. The device measures resistance in megohms, which provides an indication of the quality and effectiveness of the insulation. It is particularly useful for testing high-voltage equipment, as it identifies potential breakdown points prior to failure by determining how resistant the insulation is to leakage currents. In contrast, the other devices have different functions. An ammeter measures current in a circuit, an oscilloscope visualizes electrical waveforms, and a voltmeter measures the voltage across two points in a circuit. Each of these devices serves important roles in electrical testing, but they do not effectively evaluate insulation integrity as the megohmmeter does.