Megger Test (Insulation Resistance Test)

Megger Test (Insulation Resistance Test)

A Megger test measures the insulation resistance of the electrical equipment & wiring.

It helps keep insulation in good condition & prevents electrical leaks or short circuits.

Why is the Megger Test used?

1). Detect Insulation Weakness: Identifies insulation degradation caused by aging, moisture, or damage.

2). Prevent Electrical Failures: Assists in avoiding short circuits and electrical risks.

3). Ensure Safety: Confirms that the insulation can withstand voltage stress without leakage.

4). Compliance with Standards: Ensures that equipment complies with safety regulations.

How does Megger Test Work?

A Megger (Megohmmeter) provides a high DC voltage (500V, 1000V, or higher) to the insulation.

It measures the resistance (in MΩ) between conductors & the ground (or) between phases.

High resistance implies good insulation, whereas low resistance suggests insulation failure.

How to Perform a Megger Test?

1). Turn off the power and ensure the circuit is get de-energized.

2). Connect the Megger. One lead goes to the conductor. The other lead connects to the earth or another conductor.

3). Use Test Voltage - Determine the suitable voltage depending on system needs.

4). Measure Insulation Resistance - Check the figure on the Megger display.

5). Interpret the results.

  • Above 1 ΜΩ indicates good insulation.
  • Between 0.1 ΜΩ and 1 ΜΩ, there is a warning of probable degradation.
  • Insulation failure occurs below 0.1 ΜΩ and requires prompt action.

Applications of the Megger Test

  • Power cables
  • Motors & Generators
  • Transformers
  • Switchgear and control panels