The DC Service switch is connected to which bus?

The DC Service switch is connected to which bus?

• A. APU Battery Direct Bus
• B. Main Battery Direct Bus
• C. DC Emergency Bus
• D. DC Essential Bus

Answer: (A)

The DC Service switch is used to power the DC Service Bus from the APU Battery Direct Bus. This arrangement keeps nonessential service loads—like cabin lighting and other service equipment—operating off a dedicated DC source when the APU battery is available, without tying them into the essential or emergency power paths. The DC Emergency Bus and DC Essential Bus serve critical and emergency functions, so they’re not used to feed service loads. Using the APU Battery Direct Bus as the source for the DC Service Bus ensures service equipment can run independently of the main or essential power paths, which is why this option is the correct one.

The DC Service switch is used to power the DC Service Bus from the APU Battery Direct Bus. This arrangement keeps nonessential service loads—like cabin lighting and other service equipment—operating off a dedicated DC source when the APU battery is available, without tying them into the essential or emergency power paths. The DC Emergency Bus and DC Essential Bus serve critical and emergency functions, so they’re not used to feed service loads. Using the APU Battery Direct Bus as the source for the DC Service Bus ensures service equipment can run independently of the main or essential power paths, which is why this option is the correct one.