How fuses work？

As an overcurrent protective device, the fuse acts as “electricity’s safety valve” by providing a weak link in the circuit path that, when properly applied, will melt and open the circuit to minimize or eliminate any damage that can be caused by an excessive flow of current.  So we can see fuse is a HERO to protect the circuit.

What does a fuse do? 

A fuse protects a system or equipment from overload and short-circuit faults by cutting off the power to them. It achieves this by melting or vaporising of the fuse element so that there is no physical connection conductive path for the current flow through.

So how fuse is working in an overcurrent circuit?

A fuse consists of a piece of wire made of a metal or an alloy of an appropriate melting point, for example, aluminum, copper, iron, lead etc. If a current larger than the specified value flows through the circuit, the temperature of the fuse wire increases. This melts the fuse wire and breaks the circuit.

Overcurrent protection

An overcurrent is either an overload, a short-circuit  or ground fault current. The overload current is an excessive current flow relative  to normal operating current, but still confined to the normal circuit paths provided by the conductors, electrical components and loads. A short-circuit or ground fault currents flow outside of the normal circuit paths.

Overloads

Overloads are most often between 1.35 and 6 times the normal current level. They are usually caused by harmless, temporary in-rush currents that occur when motors start up or transformers are energized. Such overloads, or transients in short time and then back to normal as soon as possible, are normal occurrences, and their brief duration is not harmful to circuit components as the associated temperature rise is minimal with no harmful affect. It’s important that Over Current Protective Devices are properly sized and have the appropriate operating characteristics so they do not react to these temporary overloads or cause “nuisance openings.”

Persistent, non-temporary overloads can result from defective motors (worn bearings) or when too many loads are  on  a  single  circuit  and must not be permitted to last long enough to damage electrical system components such as conductors. This damage may eventually lead to severe fault events if the overload is not interrupted.

Due to the overload’s inherent low magnitude nature, removing them within seconds or even minutes will generally prevent thermal damage.

Short-circuits

Short-circuits differ from overloads as they can be hundreds to thousands of times greater than the normal operating current. A high level short-circuit may be up to 30 kA or 200 kA, and must be interrupted as quickly as possible to minimize the damage that can include:

•High magnetic forces that warp and distort busbars and associated bracing beyond repair

•Severe insulation damage

•Melting or vaporizing conductors

•Vaporizing metal, including busswork in electrical equipment

•Ionized gases

•Arcing fires

•Explosions

In fuse, the breaking capacity is solving the short-circuit problem.