Carbon Brush Types and Commutation

The term “carbon brush” appeared in electrical engineering history with the change to materials actually made from copper wire, which looked like a brush, to graphite and carbon. Carbon brushes have been evolving for decades. Today, they remain indispensable hardware for DC electrical machines.

Carbon Brush Designs

Solid, one-piece carbon brushes: Solid brushes are the simplest type of brush used on the most basic of machines with little or no electrical and/or mechanical considerations.

Fractional HP brushes: These carbon brushes are also called "spring-loaded" because of the attached spring used to load the carbon in the brushholder.  Most of these applications are one piece, however, FHP brushes can also be split.  

Split Carbon Brushes: Split bushes are designed by bringing together 2, 3, or more carbon sectors into one unit, resulting in optimal electrical and mechanical contact. Splitting the brush allows for more electrical contact points between the brush surface and commutator and evenly distributed pressure or 'riding'capacity.  The carbons can be held together by a riveted clip, however, in most modern applications, they are glued to a rubber hard top.

Carbon Brush Commutation

Brush grades should be chosen by considering various things, like atmospheric conditions, for the best commutation. Commutation (commuting current to complete the circuit) occurs when two or more carbon brushes contact the commutator. For further information on brush grades, see “Replacing Carbon Brushes for Electric Motors”.

Contact a REPCO carbon brush specialist for help in choosing the carbon brush type best suited for your application. Call 800.822.9190 or submit a contact request online.