Most overload relays used on modern motor starters are magnetically operated and consist of two strips of metal welded together.

• A. They are plastic
• B. False
• C. They are never welded
• D. True

Answer: (B)

Overload protection in motor starters is typically thermal. A thermal overload uses a bimetallic element—two strips of different metals welded together. As current passes and heats the element, the metals expand at different rates, causing the strip to bend and trip the switch. This heat-responsive behavior is the hallmark of most modern overload relays, which is why the description of them as magnetically operated and made from welded metal strips isn’t accurate.

Magnetic overload trips do exist, using an electromagnet to actuate the trip, but they’re not the most common design in modern motor starters. The standard devices rely on the heating of the bimetal element, not a magnetic mechanism.