A Megger is a portable instrument used to measure the insulation resistance of electrical wiring, cables, motors, transformers, and other electrical equipment. It is commonly used in maintenance, troubleshooting, and testing applications to assess the insulation integrity and detect potential faults or breakdowns in electrical insulation.

The name "Megger" is derived from the company Megger Group Ltd., which originally manufactured insulation testers and continues to be a prominent manufacturer of such equipment.

The primary function of a Megger is to apply a high-voltage DC (direct current) test voltage to the insulation being tested and measure the resulting insulation resistance. This test helps determine whether the insulation is adequate to prevent leakage currents and electrical faults that could lead to short circuits or electrical hazards.

Key features of a Megger typically include:

1. High Test Voltage: Meggers typically apply test voltages ranging from 50 volts to several thousand volts, depending on the application and the insulation resistance being tested. Higher test voltages are used for testing larger or higher voltage equipment.

2. Insulation Resistance Measurement: Meggers measure the insulation resistance in ohms, indicating how effectively the insulation material can resist the flow of electrical current. Insulation resistance values are typically displayed on the instrument's digital or analog display.

3. Test Leads and Probes: Meggers come with test leads and probes that connect the instrument to the electrical equipment being tested. The test leads are insulated to prevent electrical shock and ensure accurate measurements.

4. Resistance Range Selection: Meggers often have multiple resistance measurement ranges to accommodate different insulation resistance levels and test conditions. Users can select the appropriate range based on the expected insulation resistance of the equipment being tested.

5. Guard Terminal: Some Meggers feature a guard terminal or guard circuit that helps minimize the effects of surface leakage currents and stray capacitance, ensuring accurate insulation resistance measurements.

6. Safety Features: Meggers incorporate safety features such as overload protection, voltage interlocks, and insulation barriers to protect the operator from electrical hazards and ensure safe operation.

Overall, Meggers are essential tools for assessing the condition of electrical insulation in various industrial, commercial, and residential applications. Regular insulation resistance testing with a Megger helps identify potential insulation problems early, prevent electrical failures, and ensure the safety and reliability of electrical systems.