Using a brush grade unsuitable for the machine and duty can lead to which wear pattern?

• A. Grooving
• B. Streaking
• C. Arc burns
• D. Bearing wear

Answer: (A)

Using a brush grade that isn’t suited to the machine and duty changes how the brush interacts with the commutator. If the grade is too hard or otherwise unsuitable for the operating conditions, the brush can act like a cutting tool rather than a smooth sliding contact. As the brush wears, it bites into the copper and wears along longitudinal lines, creating parallel grooves on the commutator surface. These grooves are a telltale sign that the brush material and the machine’s operating demands aren’t matched, and they can lead to uneven current transfer and heat.

Streaking and arc burns point to other issues, such as uneven contact or improper commutation, and bearing wear is a mechanical issue unrelated to brush grade. But grooving directly reflects the improper brush–duty pairing and is the pattern you’d expect from using an unsuitable brush grade. To fix it, choose a brush grade matched to the current density, speed, and commutator material, and ensure proper seating and break-in.