What is the purpose of a bus tie in an aircraft electrical system with multiple generators?

• A. To permanently connect two buses
• B. To automatically ground the system
• C. To connect external power only
• D. To allow switching between power sources and isolate a generator, maintaining power to essential buses

Answer: (D)

In an aircraft with multiple generators, the bus tie serves as a controllable bridge between power buses so you can manage how sources feed the electrical system. When the bus tie is closed, the two buses are connected, allowing generators to share current and, if needed, transfer power from one source to another. If a generator fails or needs to be taken offline, the bus tie can be opened on that side to isolate that generator while the other generator (or an external source) continues to power the essential buses. This setup ensures continuous power to critical systems even when one generator isn’t available. It also enables parallel operation for load sharing during normal conditions. The bus tie is not primarily for automatic grounding or only for external power; its main purpose is to allow switching between power sources and isolate a generator while maintaining power to essential buses.