Definition
A central electrical conductor in the aircraft's electrical system to which the main power sources (battery and alternator/generator) are connected and from which power is distributed to the various electrical circuits and components, including the starter circuit.
Plain English
A common metal strip or bar inside the aircraft that acts as the shared power point. The battery and alternator feed power into it, and the aircraft's electrical equipment draws power from it.
Context Anchor
Seen in aircraft electrical system and starting system diagrams, especially when tracing how battery power reaches aircraft equipment after the master switch is turned on.
Derivation
The word 'bus' here is short for the Latin 'omnibus,' meaning 'for all.' A bus bar is literally a bar that serves all — a single conductor that connects to many circuits at once. Knowing this helps the term feel less mysterious: it is just a shared connection point for everything electrical.
Why Pilots Care
A failed or poorly connected main power bus bar can disable multiple systems at once, including starting and essential flight instruments.
Analogy
Think of it like the main power strip for the airplane’s electrical system. Power comes into one place, then several devices receive power from that shared point.
Intuition Check
Do not read “bus” here as a vehicle, and do not read “bar” as a lever or handle. In this context, a bus bar is a shared metal electrical connection point.
Example Sentence 1
When the master switch is turned on, the battery connects to the main power bus bar and energizes the aircraft's electrical system.
Example Sentence 2
If the main power bus bar loses connection, the alternator cannot supply power to the radios or lights.