Most often, overload protection is used in reference to electrical systems. It is a safety mechanism intended to prevent or minimize damage that can occur from electrical malfunctions. Generally, if a problem occurs within an electrical circuit, the current of electricity will be automatically cut off by a protection system. Aside from electrical systems, another type of overload protection, sometimes called thermal protection, can be used to safeguard motor systems and similar devices.
Many people have had the experience of tripping a circuit breaker or blowing a fuse in their houses. This occurs because of overload protection. Most electrical systems are designed with a fail-safe mechanism, or overload relay, that senses when something has gone wrong within the circuitry and automatically cuts off electrical power in order to prevent fire or other problems from occurring.
An electrical circuit is designed to carry a certain amount of energy, or voltage. The flow of energy, called a current, should travel through the path from one point to the other unimpeded. If that current is interrupted, it causes what is commonly known as a short circuit. If an electrical system is designed properly, overload protection kicks in to stop the flow of energy until the source of the interruption is removed.
The interruption of an electrical current can occur from within the circuit itself. For instance, if an appliance such as a toaster overheats or malfunctions, it can send an excessive surge of energy through the circuit, which exceeds that which it is designed to carry. This surge will be interpreted as an interruption in the current and will often trigger overload protection. Outside sources, such as damage occurring because of a tree branch falling on a power line can also disrupt an electrical current and activate a circuit's overload protection.
Depending upon where within the circuitry a problem occurs, the power can be cut off to an isolated section or to the entire electrical system. For instance, using the example of a residential electrical system, if a person’s hair dryer malfunctions, it can cause a circuit breaker to trip, affecting only the outlet the hair dryer was plugged into. On the other hand, an electrical surge caused by a lightning strike might cause the main circuit breaker in the house to trip, cutting off power throughout the entire home. Similarly, if a tree falls on an outside power line, electrical power to an entire neighborhood could be cut off because of the location of the interruption.
Another type of overload protection, often called thermal overload protection, is built into certain mechanical devices such as motors or engines. In this instance, the protection is designed to prevent damage within a motor or other similar device caused by overheating. Overload relays within a motor, engine, or other device are designed to respond to excessive internal temperatures and will automatically shut down power within the unit in order to prevent permanent damage and allow for a forced period of cooling.