Resettable Fuses
Resettable fuses or thermal device circuit breakers, are designed to trip during a short circuit or overload to protect components and equipment from electrical faults. The tripping element is a bimetal strip made of steel and zinc and an electrical heating element. When exposed to an overcurrent, one metal expands faster than the other causing the bimetal strip to snap open. The spring-loaded contact mechanism is tripped and the flow of current is halted.
Thermal device circuit breakers come in three types of reset methods. Type I resets automatically after the bimetal strip cools. If the overcurrent is not removed, the breaker will continue to cycle on and off until the cause is corrected. Type II is non-cycling and will not reset until the until the overcurrent is removed or the power is shut off. Type III is reset manually by an external button or lever.
Resettable fuses vs Traditional fuses Traditional fuses completely stop the flow of current after they have been blown and must be replaced. Resettable fuses may still allow the equipment to operate, except in extreme cases. Because they reset automatically, they are a better choice for applications where overcurrent events are expected to occur more often or for circuits that are difficult to access or may be in remote locations.
Fuses are safety devices that are intended to provide protection to both equipment and people in the event of a power surge or an overcurrent situation. A fuse can provide this protection by using a small piece of wire that is sacrificial, and is intended to burn up when too much current is passed through it. When this happens, the fuse eliminates the flow of electricity in that circuit until it is replaced. The size and type of wire that is used in the fuse will dictate how much current can pass through that individual fuse. So the main thing to remember is, when a fuse blows, it must be replaced and cannot be reused.
Circuit breakers are intended to be reused after they are “tripped” during a power surge or an overcurrent situation. Much like fuses, circuit breakers are designed to trip at a certain current level. This is intended to protect both equipment and anyone in the area of that particular circuit. Circuit breakers can be found in just about any variation from single phase, low current applications to three phase, and high current applications.
As a general rule: fuses are more simplistic and reliable. They cost less initially and are better suited for individual circuit protection. However, they can create more cost over time with each use and may create hazards due to the exposed connection points. Whereas circuit breakers offer better branch circuit protection and do not need to be replaced after each use. They are more expensive initially and, because of their complexity, are more prone to failure over time.