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Brush spring pressure that is too high causes

  • A.an increase in the contact resistance of the brush
  • B.the brush to lift clear of the commutator at speed
  • C.rapid wear of the brush and the commutator
  • D.intermittent contact and sparking at the brush edges

Answer: C

Correct answer: rapid wear of the brush and the commutator

Excessive pressure increases the friction and the mechanical work at the contact, so both the brush and the copper wear quickly and the machine runs hot. Too little pressure gives the opposite fault - the brush bounces, contact becomes intermittent and sparking follows - so the pressure is specified within a range.

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