Electrical carbon is a conducting material made from graphite and other forms of carbon. While its conductivity is less than copper or aluminum, carbon has a smoother surface and is therefore used to make brushes in electrical machines. Carbon brushes undergo graphitizing or heat treatment to increase conductivity and reduce hardness. Graphite exhibits a negative temperature coefficient of resistance, where resistance decreases as temperature increases, keeping the brush drop voltage constant.

1. Electrical Carbon (Conducting Material)
Fig 1. Electrical Motor with Carbon Brushes

2. Electrical Carbon (Conducting Material)
• This material is made from graphite and other form of carbon.
• Conductivity of Carbon is less then Copper (Cu) and Aluminum (Al) but its
surface is smoother so it is used to make brushes in a Electrical Machine.
• Carbon brushes are graphited or heat treated to increase conductivity and
reduce hardness.
• Graphite has negative temperature coefficient
R=Ro(1-αΔT)
as Temperature increases Resistance decreases
Brush drop Voltage (VBD=IR=Constant)