Definition
An electrical bus bar in an aircraft that remains energized directly from the battery at all times, regardless of whether the master switch is on or off. It supplies power to a small number of essential or always-available circuits, such as the clock, certain emergency lights, or items that must function before the master switch is turned on.
Plain English
A power strip inside the airplane that is always live, drawing straight from the battery even when the airplane is switched off. Only a few specific items are connected to it — things that need power around the clock or before startup.
Context Anchor
Seen in aircraft electrical-system descriptions and in equipment wiring discussions, including warning systems that may need a dependable power source.
Derivation
In electrical work, a 'bus bar' is a metal strip that distributes power to multiple circuits. 'Hot' is electrician's slang for 'live' or 'energized.' So a hot bus bar is simply a distribution strip that is always live.
Why Pilots Care
Guarantees that terrain-warning and other essential systems stay available during all phases of flight and ground operations.
Intuition Check
Hot does not mean warm here; it means electrical power is present. Bus bar does not mean a vehicle; it is a shared metal path that sends power to equipment.
Example Sentence 1
The cockpit clock is wired to the hot bus bar so it keeps running between flights.
Example Sentence 2
During preflight the pilot confirmed that the hot bus bar still supplied voltage to the warning systems after the battery switch was turned off.