Advantages
*They provide good commutation.
*If sparking occurs they damage the commutator less than with the copper brushes.
*They lubricate and polish the commutator.
Disadvantages
*Contact resistance is high and cause a loss of about 2 V.Hence they are not suited for low voltage machines.
*Due to high voltage drop , the commutator must be made larger than that for copper brushes.
*Due to the low current density large brush holders are required.
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