What is the most common cause of motor failure?

• A. Power surge
• B. Bearing failure
• C. Thermal overload
• D. Grit contamination

Answer: (C)

Heat buildup is the most common reason motors fail. A motor creates heat as it runs, and if it’s pushed beyond its fuel—meaning the load is higher than the nameplate rating or cooling is blocked or inefficient—the winding insulation and bearings overheat. Repeated or prolonged overheating speeds up insulation deterioration, raises the risk of insulation failure, and accelerates wear on components, eventually leading to motor failure. Protective devices help, but persistent overheating from overload or poor cooling remains the primary driver of motor deaths. Other issues like power surges, grit contamination, or bearing problems can cause trouble, but they’re typically secondary or symptomatic of underlying overheating or maintenance gaps. To prevent this, keep the motor load within spec, ensure good ventilation and cooling, and monitor temperature and current to catch overheating early.