Definition
A sliding electrical contact, typically made of carbon or a carbon-graphite composite, that rides against the rotating commutator or slip rings of a generator, alternator, or electric motor to conduct current between the stationary and rotating parts of the machine.
Plain English
A small block of carbon that presses against a spinning part inside a generator or motor so electricity can flow into or out of the moving piece.
Context Anchor
Seen in aircraft electrical-system maintenance, especially when discussing starters, generators, alternators, and worn electrical contacts.
Derivation
Called a 'brush' because the earliest versions were literally bundles of copper wire shaped like a small brush that swept against the commutator. The name stuck even after the design changed to solid carbon blocks.
Why Pilots Care
Worn brushes cause charging system failures that can drain the battery and lose avionics power in flight.
Intuition Check
Brush does not mean a cleaning brush here. In this aviation maintenance context, it means an electrical contact that lightly touches a moving part while allowing electricity to pass.
Example Sentence 1
The mechanic replaced the worn brushes in the starter generator after noticing arcing during engine start.
Example Sentence 2
During the 100-hour inspection the technician checked brush length and spring tension.