What two considerations must be evaluated when selecting wire size for an aircraft installation?

What two considerations must be evaluated when selecting wire size for an aircraft installation?

• A. System voltage and color
• B. Current-carrying capability and voltage drop
• C. Ambient temperature and altitude
• D. Number of wires in bundle and insulation color

Answer: (B)

The key idea is to size the conductor so it can carry the required current without overheating and so it doesn’t waste too much voltage along the run. First, current-carrying capability (ampacity) ensures the wire can carry the expected load without the insulation overheating. In aircraft installations, the ampacity is influenced by the insulation, how the wire is installed, and the surrounding temperature. If the current is too high for the chosen size, the conductor can heat up excessively, risking insulation damage or fire. Second, voltage drop ensures enough voltage remains at the load to operate it properly. The resistance of the wire causes voltage to fall as current flows, and longer runs or higher currents worsen this drop. If the drop is too large, components won’t receive enough voltage to function correctly, even if the wire doesn’t overheat. Other factors like ambient temperature or altitude can affect ampacity, but they’re considerations that modify the sizing, not the two fundamental criteria described above.

The key idea is to size the conductor so it can carry the required current without overheating and so it doesn’t waste too much voltage along the run.

First, current-carrying capability (ampacity) ensures the wire can carry the expected load without the insulation overheating. In aircraft installations, the ampacity is influenced by the insulation, how the wire is installed, and the surrounding temperature. If the current is too high for the chosen size, the conductor can heat up excessively, risking insulation damage or fire.

Second, voltage drop ensures enough voltage remains at the load to operate it properly. The resistance of the wire causes voltage to fall as current flows, and longer runs or higher currents worsen this drop. If the drop is too large, components won’t receive enough voltage to function correctly, even if the wire doesn’t overheat.

Other factors like ambient temperature or altitude can affect ampacity, but they’re considerations that modify the sizing, not the two fundamental criteria described above.