What is the key principle behind the voltage drop testing method?

What is the key principle behind the voltage drop testing method?

• A. Disconnect power completely
• B. Test current must flow in the circuit
• C. Use a megohmmeter
• D. Measure voltage without load

Answer: (B)

Voltage drop testing rests on Ohm's law: you need current flowing through a path to see a voltage drop. When you pass a known test current through a conductor or connection, any resistance there—due to a loose lug, corrosion, or a damaged contact—causes a measurable drop in voltage across that point. The bigger the drop, the higher the resistance, which points you to the fault location. Without current, there’s essentially no voltage drop to measure, so you can’t identify faults under load. A megohmmeter and insulation tests measure resistance in a different way, not the normal under-load voltage drop. Measuring voltage with no load also won’t reveal the problem because the drop requires current to produce it.

Voltage drop testing rests on Ohm's law: you need current flowing through a path to see a voltage drop. When you pass a known test current through a conductor or connection, any resistance there—due to a loose lug, corrosion, or a damaged contact—causes a measurable drop in voltage across that point. The bigger the drop, the higher the resistance, which points you to the fault location. Without current, there’s essentially no voltage drop to measure, so you can’t identify faults under load. A megohmmeter and insulation tests measure resistance in a different way, not the normal under-load voltage drop. Measuring voltage with no load also won’t reveal the problem because the drop requires current to produce it.