Which type of load is more destructive to the switching contacts of control devices?

• A. Resistive loads
• B. Inductive loads
• C. Motor starter coils
• D. Capacitive loads

Answer: (C)

Motor starter coils are particularly destructive to the switching contacts of control devices due to the nature of the inrush current and inductive kickback they produce. When a motor starter coil is energized, it draws a high inrush current, which is significantly greater than the normal operating current. This high current can create excessive heating and contact pitting as the contacts attempt to open and close during operation.

Additionally, when the contacts of a motor starter coil open, the magnetic field in the coil collapses rapidly, inducing a high voltage spike (also known as back EMF) across the contacts. This back EMF can cause arcing, leading to further deterioration of the contact surfaces. Over time, this results in increased wear and potential failure of the contacts, making motor starter coils particularly harmful compared to resistive loads, inductive loads, and capacitive loads, which have less severe effects on contact wear and arcing.