Definition
A switch or relay in an aircraft electrical system that connects two separate electrical buses together, allowing power from one source to feed both buses, or isolating them from each other when opened.
Plain English
A switch that links two electrical supply lines in the airplane so they can share power, or splits them apart so a problem on one side does not affect the other.
Context Anchor
Seen in aircraft electrical system descriptions, cockpit electrical panels, and abnormal checklists for generator or alternator failures.
Derivation
A 'bus' in electrical systems is a common conductor that distributes power to multiple circuits — the name comes from 'omnibus,' Latin for 'for all,' since the bus serves all connected loads. 'Tie' simply means a connection between two things. So a bus tie is a connection between two power-distribution lines.
Why Pilots Care
Provides redundancy so a failed generator or bus does not immediately disable essential equipment.
Analogy
Think of two rooms with separate lights and a door between them. Opening or closing the door controls whether the rooms are connected; a bus tie does that for parts of the electrical system.
Intuition Check
“Bus” does not mean a vehicle here, and “tie” does not mean a rope or knot. In this context, a bus tie is an electrical link that connects or separates power-distribution points.
Example Sentence 1
After the left generator failed, the pilot closed the bus tie so the right generator could power both electrical buses.
Example Sentence 2
The checklist calls for verifying bus tie operation before flight to confirm electrical redundancy is available.