How is a voltage drop test performed on an aircraft wiring circuit, and what does it diagnose?

• A. Measure the voltage across a terminal under load; a larger-than-expected drop indicates poor connections or damaged conductors
• B. Measure the resistance of a wire segment with no load
• C. Check insulation continuity with megger
• D. Compare battery voltage to a standard

Answer: (A)

A voltage drop test checks how much voltage is lost in a circuit when it is carrying normal current, which reveals high resistance at connections or along conductors. To perform it, energize the circuit and measure the voltage at the source and at a point farther along the path while the circuit is under its usual load. The difference between the supply voltage and the voltage at the test point is the voltage drop. If this drop is larger than what the system allows, there’s excessive resistance somewhere in that segment—commonly a loose or corroded connection, damaged or frayed wire, or an undersized conductor. To locate the issue, compare drops across multiple sections or test successive segments; the spot with the largest, unacceptable drop points to the fault area. This method reveals real-world losses under operating conditions, unlike a no-load resistance check or insulation tests, which don’t reflect how voltage is actually used in the circuit.