Which instrument is used for checking insulation resistance on motors, feeders, bus bar systems, grounds, and branch circuit wiring?

• A. An instrument used for measuring voltage on circuits.
• B. An instrument used for checking insulation resistance on motors, feeders, bus bar systems, grounds, and branch circuit wiring.
• C. A device for measuring current in amperes.
• D. A tool for testing continuity of conductors.

Answer: (B)

Insulation resistance testing measures how well the insulating material isolates conductors from each other and from ground. To do this reliably you need an instrument that can apply a high voltage and measure the resulting resistance; that tool is an insulation resistance tester, commonly called a megohmmeter or megger. This is the ideal choice for motors, feeders, bus bar systems, grounds, and branch circuit wiring because these components rely on solid insulation to prevent leakage currents and electrical faults.

The tester powers the insulation with a high DC voltage and reports resistance in megohms. A high megohm reading indicates good insulation, while a low reading points to leakage paths caused by moisture, contamination, aging, or damage. Tests are performed with the equipment de-energized, proper safety procedures observed, and results compared against applicable standards or manufacturer recommendations.

Other instruments that measure voltage, current, or continuity do not assess insulation integrity and thus aren’t suitable for this purpose.