Which of the following is listed as a possible cause of high mica besides Normal Wear / Loosening?

• A. Heavy Slot Bar Marking
• B. Light Brush Pressure
• C. Abrasive Brush
• D. Airborne Contaminants

Answer: (A)

High mica means more insulation material (mica) has been exposed or shed than normal wear would cause. The most plausible listed cause besides normal wear/loosening is heavy slot bar marking. When slot bars contact the winding with excessive or rough pressure, they can gouge or score the mica insulation inside the slots. That mechanical damage loosens or removes mica, leading to a higher mica reading or visible mica flakes. The other options don’t fit this damage mechanism: light brush pressure isn’t enough to remove mica, an abrasive brush would imply harsh cleaning but isn’t the commonly cited cause here, and airborne contaminants don’t directly explain an increase in exposed mica.