In aircraft wiring, which color code is used for grounding in DC circuits?

• A. Black commonly used for negative/ground in DC; red for positive/hot; green or green-yellow for grounding or special circuits per OEM.
• B. Red commonly used for negative; Black for positive; Green for data lines.
• C. Green commonly used for negative; Red for positive; Black for grounding.
• D. Black commonly used for positive; Red for negative; Green for grounding.

Answer: (D)

In DC aircraft wiring, the grounding path is shown with green, so you can quickly identify the chassis or earth connection separate from the power paths. The two DC power conductors carry the supply and are colored to indicate polarity. In the convention used here, the positive conductor is black and the negative conductor is red, while green marks the grounding. This separation helps prevent mix-ups between the power path and the ground path, which is crucial for safe maintenance and fault diagnosis. Always check the specific OEM wiring diagrams for any variations, but the general idea is green = grounding, with the other two colors indicating the DC supply polarity.