When brush spring pressure is too what, the brushes can arc excessively due to the poor electrical contact?

• A. Light
• B. Medium
• C. Heavy
• D. Very light

Answer: (D)

The amount of brush spring pressure sets how firmly the carbon brush presses against the commutator. When that pressure is very light, the brush doesn’t stay in solid contact as the machine runs. The contact becomes erratic, with high or changing contact resistance, and small gaps allow current to jump—causing sparking or arcing at the surface. This excessive arcing harms both the brush and the commutator and indicates the need for more spring tension to maintain proper, stable contact. If you push the spring pressure higher, you’ll typically reduce arcing, though it’s important to stay within the specified range to avoid other problems like excessive brush wear or overheating.