Liquid solvent can carry particles deep into hidden recesses of a DC generator or motor. This is especially true of the spaces around which risers?

• A. rotor
• B. stator
• C. end bells
• D. commutator

Answer: (D)

Capillary action in tight, narrow gaps lets liquid solvent wick into recessed areas of a DC machine. The commutator sits in a confined pocket and is surrounded by brush gear, mica insulation between bars, and close-fitting end bells. These tiny spaces and slots create easy paths for solvent to travel from the surface into deeper recesses, carrying abrasive particles with it. Because the commutator is the interface for the brushes and holds the fragile insulating gaps between segments, any contamination that reaches there can be trapped and spread deeper into the interior. The rotor and stator pockets are not as accessible to exterior solvent in the same way, and the end bells are external housings, so the commutator area is the most vulnerable point for solvent intrusion.