Which of the following is a common cause of motor failure?

Electrical overload is indeed a common cause of motor failure because it can lead to overheating. When a motor operates beyond its rated load, it draws more current than it is designed to handle. This excess current causes the windings within the motor to heat up significantly, potentially damaging insulation and leading to shorts or open circuits. Moreover, prolonged electrical overload can degrade the motor's performance and lifespan, ultimately resulting in complete failure.

In contrast, excessive lubrication may not directly cause a motor to fail, but it can lead to issues such as increased friction or even leakage, which might disrupt the motor's operation. Frequent starting and stopping can wear down components, but with proper design, many motors can handle such cycles without detrimental effects. Using smaller wire gauges increases resistance and can lead to voltage drops or overheating, but it’s not as straightforwardly linked to motor failure as electrical overload is. Overall, electrical overload stands out as a primary concern when discussing the failure modes of electric motors.