Which condition leads to excessive brush wear?

• A. Too much pressure
• B. Too little pressure
• C. No pressure
• D. Varying pressure

Answer: (A)

Excessive brush wear happens when brushes are pressed too hard against the commutator. The carbon brushes rely on a controlled contact force from the springs; if that force is too high, friction at the contact face increases dramatically, causing faster material loss from the brush and more heat at the surface. The extra heat can soften or smear the brush material and gouge the commutator, leading to accelerated wear and potential damage. Maintaining the correct brush tension keeps contact steady without excessive rubbing, promoting longer brush life and smoother operation.

Too little pressure leads to poor electrical contact and arcing, which can cause sparking and uneven wear but not the rapid, excessive wear caused by too much pressure. No pressure stops contact altogether, and varying pressure creates uneven wear rather than consistently excessive wear.