An overload breaker is designed to protect which of the following?

An overload breaker is specifically designed to provide protection for electrical motors from overloading. When a motor experiences excessive current due to mechanical overload, it can draw more power than it is rated for, which can lead to overheating and potential damage. The overload breaker responds to this increased current, interrupting the electrical supply to the motor before it can sustain damage. This mechanism ensures that motors operate safely within their design limits, preventing costly repairs or potential safety hazards such as fire.

While power supply units, light fixtures, and circuit boards do have their own protective devices and safety measures, they do not typically rely on an overload breaker for protection against effects of overload in the same manner as electrical motors do. Therefore, the correct answer highlights the specific role of overload breakers in safeguarding motors in electrical systems.