What are Carbon Brushes and How Do They Work?

A carbon brush, also known as a motor brush, is a very small part of an electric motor that conducts the electrical current between stationary and rotating wires inside the motor/generator.

Carbon brushes are typically made from one or multiple carbon blocks (including copper graphite, natural graphite, electro graphite, silver graphite, bonded carbon, and pitch bonded carbon), with one or more terminals. Carbon is used as it's a reasonably good conductor of electricity, while it is soft enough to give a consistent contact point. However this soft property means it does wear over time, and hence the need to regularly replace carbon brushes.

You will typically find more than one carbon brush in each motor, and there are different types for different types of motors/tools.