Which combination of factors is cited as the normal cause of electric motor failure?

• A. Dirt, moisture, and friction
• B. Overheating
• C. Electrical noise
• D. Misalignment

Answer: (A)

Contamination of the bearings with dirt and moisture is a common root cause because it directly undermines lubrication and promotes wear. Dirt and water get into the bearing housing and mix with the lubricant, breaking down the grease film that keeps surfaces from rubbing. That dirty, thin film means the moving parts run with more metal-to-metal contact, so friction rises and heat builds up. The extra friction accelerates wear on bearings and can damage seals and insulation, leading to failure of the motor.

In many industrial settings, this combination—dirt and moisture causing lubrication breakdown and increased friction—explains a large share of motor failures. Overheating, while important, is often a symptom or consequence of that same wear and poor lubrication, rather than the standalone normal cause. Misalignment or electrical noise can cause problems too, but they don’t represent the most typical, combined root cause as cleanly as contamination with moisture does.