A _______ is used to check for insulation breakdown in armatures and fields.

A _______ is used to check for insulation breakdown in armatures and fields.

• A. Megger
• B. Ohmmeter
• C. Voltmeter
• D. Ammeter

Answer: (A)

Testing insulation integrity of windings is done with an insulation resistance check, which requires an instrument that can apply a high voltage and measure how much leakage current occurs. A megger is built for this purpose, often called an insulation tester. It provides a high DC voltage across the winding and measures the resulting leakage current, giving a resistance value in megohms. A high resistance indicates good insulation with little leakage to the core or frame, while a low resistance reveals insulation breakdown or moisture/deterioration. This is essential for armatures and fields because you’re assessing the insulation between windings and between the windings and grounded parts. Ordinary low-voltage tools can’t reliably reveal breakdown that only shows up under higher voltage stress, which is what the megger mimics. Other instruments don’t fit this job. An ohmmeter checks continuity at low voltage and can’t test insulation resistance under high-voltage stress. A voltmeter only measures voltage, not how well insulation resists leakage. An ammeter measures current flow during operation, not the condition of insulation. The megger uniquely provides the high-voltage insulation resistance reading needed to detect insulation breakdown.

Testing insulation integrity of windings is done with an insulation resistance check, which requires an instrument that can apply a high voltage and measure how much leakage current occurs. A megger is built for this purpose, often called an insulation tester. It provides a high DC voltage across the winding and measures the resulting leakage current, giving a resistance value in megohms. A high resistance indicates good insulation with little leakage to the core or frame, while a low resistance reveals insulation breakdown or moisture/deterioration.

This is essential for armatures and fields because you’re assessing the insulation between windings and between the windings and grounded parts. Ordinary low-voltage tools can’t reliably reveal breakdown that only shows up under higher voltage stress, which is what the megger mimics.

Other instruments don’t fit this job. An ohmmeter checks continuity at low voltage and can’t test insulation resistance under high-voltage stress. A voltmeter only measures voltage, not how well insulation resists leakage. An ammeter measures current flow during operation, not the condition of insulation. The megger uniquely provides the high-voltage insulation resistance reading needed to detect insulation breakdown.