What is the expected color coding for positive and negative conductors in a typical 28V DC aircraft system?

• A. Positive conductors are red or brown; negative/ground are black or blue, though exact colors vary by manufacturer.
• B. Positive conductors are blue; negative are red.
• C. Both positive and negative are black.
• D. Positive conductors are green; negative are yellow.

Answer: (A)

In typical 28V DC aircraft systems, polarity is indicated by color to prevent miswiring and protect components. Positive conductors are colored red or brown, while negative or ground conductors are black or blue. This convention helps maintainers quickly identify connections and reduce the risk of damage or safety issues in a demanding environment. Remember that exact colors can vary by manufacturer, so always check the aircraft’s wiring diagrams or maintenance manual. Colors like blue for a positive conductor or green/yellow for DC lines don’t fit the common aviation practice and can cause confusion, since green/yellow is usually used for earth grounding in many systems. The main idea to take away is red or brown for positive and black or blue for negative/ground, with some manufacturer-specific variations.