By Michael Logan, Updated Mar 24, 2022
An electric motor functions by rotating a coil of wire within a magnetic field. In many motors, carbon brushes deliver current to the rotating coil through contact with a segmented commutator, which switches the direction of current as the rotor turns.
The brushes remain stationary while the motor spins. They press against the commutator, transferring electrical power to the appropriate coil segment. As the rotor turns, each brush sequentially contacts a different segment, ensuring continuous operation.
Continuous sliding against the commutator produces wear on both the brushes and the commutator. The segmented design means brushes repeatedly engage and disengage, amplifying friction and accelerating material loss over time.
Maintaining solid contact between brush and commutator is critical. Applying ordinary grease to the brushes would increase the distance between them and the commutator, effectively breaking the electrical path. Industry practice uses graphite—a natural, conductive form of carbon—as a lubricant; it reduces friction without compromising contact.
For optimal performance, follow the manufacturer’s maintenance schedule and use only graphite‑based lubricants. Avoid greases, oils, or other non‑conductive substances on motor brushes.
