What tool is commonly used to assess insulation condition between windings and ground?

• A. A megohmmeter (megger) for insulation resistance testing.
• B. A high-precision voltmeter for voltage accuracy.
• C. An ammeter for current measurement.
• D. A wattmeter for power factor determination.

Answer: (A)

A megohmmeter is used to assess insulation between windings and ground. It applies a high DC voltage to the winding with respect to ground and measures the leakage current to determine the insulation resistance, reported in megohms. A healthy insulation shows a very high resistance, indicating minimal leakage. If the resistance is low, it signals a leakage path due to moisture, contamination, or insulation breakdown, meaning the winding’s insulation may be compromised. This direct measurement of insulation resistance is why a megohmmeter is the right tool for this check. Other devices described—voltmeter, ammeter, and wattmeter—measure voltage, current, or power, not the insulation resistance between windings and ground.