Which device is used to measure insulation resistance in electrical installations?

The device used to measure insulation resistance in electrical installations is a Megger. A Megger, or insulation resistance tester, applies a high DC voltage to the insulation being tested and measures the resistance to leakage current. This value indicates the quality of the insulation: higher resistance values suggest better insulation integrity, while lower values may indicate degradation or failure, prompting further investigation or necessary maintenance.

In contrast, other devices serve different functions. A multimeter is versatile and can measure voltage, current, and resistance, but it is not designed specifically to assess insulation resistance under high voltage. A clamp meter is primarily used to measure alternating current without disconnecting the circuit, focusing on current rather than insulation properties. An oscilloscope visualizes electrical waveforms and is not suited for measuring resistance or insulation quality. The Megger is specifically designed for this purpose, making it the correct answer for measuring insulation resistance.