What are the three categories of grounds commonly recognized in aircraft wiring?

• A. Ground straps, frame grounds, equipment grounds
• B. AC returns, DC returns, and all others
• C. Primary grounds, secondary grounds, tertiary grounds
• D. Signal grounds, power grounds, chassis grounds

Answer: (B)

Grounds are treated by the path the current takes back to its source, not by where they’re mounted. The three categories recognized are AC returns, DC returns, and all other grounds. AC returns are the return paths for alternating-current circuits, DC returns are the return paths for direct-current circuits, and all other grounds cover grounding needs that aren’t dedicated return paths for a specific power system—such as chassis, equipment bonding, shielding, and structural grounding. Keeping AC and DC returns separate helps manage impedance and noise and prevents interference between the two power systems, while the “all other grounds” set ensures consistent grounding for equipment and safety bonding without becoming part of a main current return. Other answer options describe groupings that don’t align with how aviation wiring distinguishes return paths for AC, DC, and miscellaneous grounds.