Definition
A circuit breaker in an aircraft electrical system that connects or isolates two separate electrical buses. When closed, it ties the buses together so they share power; when opened, it isolates one bus from the other to contain a fault or allow independent operation.
Plain English
A switch-like device that links two electrical supply lines in the aircraft. It can join them together so they work as one, or split 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 maintenance checks on aircraft with more than one electrical bus or power source.
Derivation
‘Bus’ in electrical use comes from ‘busbar’, a shortening of ‘omnibus bar’ — Latin omnibus meaning ‘for all’ — because the bar distributes power to all connected circuits. ‘Tie’ means to join, and ‘breaker’ refers to a circuit breaker that can interrupt the connection. So a bus tie breaker is the device that ties the buses together or breaks the tie between them.
Why Pilots Care
It lets the pilot maintain essential electrical power after a generator or bus failure while preventing faults from affecting the entire system.
Analogy
Think of two rooms with a door between them. When the door is open, people can move between the rooms; when it is closed, the rooms stay separate. A bus tie breaker is like that door for aircraft electrical power.
Intuition Check
Bus does not mean a vehicle here; it means an electrical power distribution point. Tie does not mean rope, and breaker does not mean something is broken; it means a controlled electrical switch that can connect or separate power paths.
Example Sentence 1
After the left generator failed, the crew confirmed the bus tie breaker had closed automatically so the right generator could power both buses.
Example Sentence 2
The bus tie breaker opened automatically when a short was detected on the left bus, isolating it from the right bus.