desirable. Most machines require a complete
overhauling and thorough cleaning out once a year.
Essential for satisfactory operation of brushes is
free movement of the brushes in their holders. Uniform
brush pressure is necessary to assure equal current
distribution. Adjustment of brush holders should be set
so that the face of the holder is approximately one
eighth of an inch up from the commutator; any distance
greater than this will cause brushes to wedge, resulting
in chattering and excessive sparking.
Check the brushes to make sure that they will not
wear down too far before the next inspection. Keep an
extra set of brushes available so that replacements can
be made when needed. Sand in new brushes, and run
the motor without a load to seat the brushes.
Make sure that each brush surface in contact with
the commutator has the polished finish that indicates
good contact and that the polish covers all contact
surfaces of the brush. Check the freedom of motion of
each brush in the brush holder. When replacing a
brush, be sure to put it in the same brush holder and in
its original position. It will be easier for you to replace
the brush properly if you scratch a mark on one side of
the brush before you remove it.
Check the springs that hold the brushes against the
commutator. Improper spring pressure may lead to
commutator wear and excessive sparking. Excessive
heating may have annealed the springs, in which case
you should replace them and correct the cause of
Inspect the commutator for color and condition.
The part where the brushes ride should be clean and
smooth and should be a polished brown color. A bluish
color indicates overheating of the commutator.
You should remove any roughness on the
commutator by sandpapering or stoning. Never use an
emery cloth or an emery stone. For this operation, run
the motor without load. If you use sandpaper, wrap it
partly around a wooden block. The stone is essentially
a piece of grindstone, known to the trade as a com-
mutator stone. With the motor running without load,
press the stone or sandpaper against the commutator
with moderate pressure and move it back and forth
across the commutator surface. If the armature is very
rough, it should be taken out and the commutator
turned down in a lathe.
Use care not to come into contact with moving
The electrical shop should have a record card for
every motor. As a minimum, the information on the
card should include inspections, repair work, age, and
replacement stock number.
About once a year or more often if conditions
warrant, motors should be cleaned thoroughly.
Smaller motors, the windings of which are not easily
accessible, should be taken apart.
First, remove the heavy dirt and grease with a
heavy, stiff brush; wooden or fiber scrapers; and
cloths. You can use rifle-cleaning bristle brushes in the
air ducts. You can blow-dry dust and dirt off, using
dry-compressed air at a moderate pressure, perhaps
25 to 50-psi pressure at the point of application, taking
care to blow the dirt out and away from the windings. If
the dirt and dust are metallic? conducting, or abrasive,
using air pressure is not as satisfactory as using a
When cleaning motors with compressed air,
wear safety goggles and hearing protection.
Dispose of lubricants and contaminated
materials in an environmentally responsible
You can easily remove grease, oil, and sticky dirt
by applying cleaning liquids specifically designed for
the purpose. These liquids evaporate quickly and, if
not applied too generously, will not soak or injure the
insulation. If you do use one of these liquids, be sure to
follow the manufacturers direction for use.
After new motors and controls are installed, they
should be checked for operation under load for an
initial period of at least 1 hour. During this time, the
electrician can observe if any unusual noise or hot
spots develop. The operating current must be checked
against the nameplate ampere rating. This check
requires skill in the proper connection, setting, and
reading of a clamp-on ammeter. The nameplate
ampere reading multiplied by the service factor (if any)