On Apr 29, 11:55 am, "Andy" wrote:
"David Nebenzahl" wrote in message

s.com...

On 4/27/2008 6:54 PM A. H. G. spake thus:

Can you tell me is the brushing material copper?

Since you asked, no; brushes are made of carbon.

But looking at the brushing material, it seems metallic and like copper. How
is carbon material conductive?

Carbon brush are conductive but have some resistance. Carbon is soft
and wears instead of the copper commutator. They have a copper coating
to conduct better in their brass (usually) holders.