Yale MPB040E Manual page 102

Brush and Commutator Inspection
A light brown surface of the commutator where it ro-
tates on the brushes is a normal condition. The surface
of the commutator must be smooth.
A condition called slot bar marking is also normal if the
commutator surface is smooth. The variable color oc-
curs in a pattern according to the number of conductors
per slot.
4
Table 1. Normal Commutator Surfaces
Variations between light brown and dark brown colors
are also normal. The surface of the commutator must
be smooth.
A very dark surface is also a normal and an acceptable
condition if the commutator surface is smooth.
0620 YRM 0294