Which of the following electrical components is primarily used to protect circuits from overload?

The breaker is the component that plays a crucial role in protecting circuits from overload. It automatically interrupts the flow of electricity when it detects that the current exceeds a predetermined level, thereby preventing potential damage to the electrical system or the devices connected to it. Breakers work by opening the circuit when the current exceeds safe levels, which helps prevent overheating and reduces the risk of electrical fires or equipment failure.

In contrast, a transformer is used to change the voltage levels in a circuit but does not provide overload protection. A capacitor stores energy temporarily and helps smooth out fluctuations in voltage, but it does not serve a protective function against circuit overloads. A diode is used to allow current to flow in one direction only, which is helpful in controlling current flow but does not provide circuit protection from overload conditions. Thus, the breaker is distinctly designed to fulfill the role of protection against overloads, making it the correct choice in this scenario.