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Operations, Maintenance


Brush Maintenance, Brush Wear


Summarizes the things to check and look for that would indicate time to change a brush

Knowing When to Change a Brush

Many factors influence brush wear:

  • Spring pressure

  • Ring condition

  • Current density

  • Atmospheric conditions

  • Presence of contaminants

  • Holder condition

  • Brush grade

Replace brushes before they become too short. Frequently inspect the brushes to determine if they need to be replaced by checking the wear indicator. In this example, part A shows a wear indicator on a new brush and part B shows the wear indicator of a brush that is in need of replacement.


Brushes should be changed when the top edge of the brush box is even with the wear indicator on the brush leads. Cutsforth does not recommend running brushes that are past the wear indicator, “short brushes,” as doing so could lead to negative performance, including failure. Further, running short brushes can cause the following issues:

  • Decreased spring pressure: Spring pressure is constant through the operational life of the brush but will reduce as the brush is worn past the wear indicator. Decreased spring pressure can result in a poor brush-to-ring connection and elevate the risk of arcing, abnormal ring wear, and increased brush vibration.
  • Increased brush binding: Short brushes are not supported in the brush holder as well as brushes of a proper length and tend to bind in the brush box. The brush leads on short brushes also resist the force of the spring, causing further binding problems. Brush binding will lead to poor brush-to-ring connection and attendant issues given above.
  • Selective action: Short brushes mixed with proper-length brushes can cause uneven current distribution throughout the brushes and lead to overheating problems.

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