Brushes and commutators should be inspected for condition on a quarterly schedule. VLBA motor brushes when properly maintained should last many thou- sands of hours. Intermittent sparking due to overload or slight visible sparking does not necessarily indicate poor commutation.
Poor commutation exists when there is excessive sparking requiring abnormal main- tenance.
Every case of excessive sparking should be investigated to determine the cause and correct it. Keep the interior parts of motors clean and dry. Remove dust, dirt, corrosion, grease, oil and moisture. Ventilating air filters must be kept clean or replaced to insure full volume of cooling air. Dirt or dust can be removed by wiping them with a clean cloth, by blowing with clean, dry, low pressure air or by a vacuum cleaner.