Which of the following is not a common aircraft system voltage?

• A. 12 VDC
• B. 14 VDC
• C. 230 VAC
• D. 115 VAC

Answer: (C)

The main idea is that aircraft electrical systems are built around low-voltage DC power, with AC power used only in specific, tightly defined ways. A 12 VDC system is common in light aircraft, and the alternator/charging systems often bring that up to about 14 VDC to keep the battery topped off and the electrical gear powered. Some aircraft use higher DC levels like 24 V or 28 V for larger loads or different designs, but the trend stays within DC for onboard power.

When AC is used on aircraft, it is typically 115 VAC at 400 Hz rather than 230 VAC. This lower frequency and voltage are chosen to keep transformers and generators lighter and simpler, which is important for aviation. 230 VAC is standard in many mains power systems on the ground, but it is not a typical onboard system voltage for aircraft.

So, 230 VAC isn’t a common onboard aircraft system voltage, while the other options align with the voltages you’ll actually encounter in aircraft electrical systems.