Circuit Breakers and Fuses

This is for all those who dwell in the arena of electrical devices and mechanisms. Many of us might have heard and some of us might even know what a circuit breaker is. Those who do not have them installed at home mostly know fuses. Both these electrical tools are meant more or less for the same purpose. The purpose is to prevent the damage to an electrical circuit by cutting the power supply at that point. A circuit breaker and a fuse are absolutely essential for an electrical circuit to be in proper shape. Let's look at these two - how they work and how they are different and similar to each other.

Circuit Breakers

It refers to an automatically operated electrical switch, which is made in such a way that it shields an electrical circuit from any harm as a result of overload or a short circuit. Primarily it finds a fault condition, disrupts the continuity to instantly discontinue electrical flow. This makes its installation an indispensable part in any electrical circuit. These are made in different sizes, from miniature for domestic purposes to huge switchgear meant to protect high voltage circuits supplying electricity to an entire city.

Types
Low Voltage: These are common in a domestic, commercial and industrial set up. Their capacity is less than 1000 V. These include miniature size and Molded Case Circuit Breaker (MCCB). The former has a rated current not more than 100 A. The characteristics are usually not adjustable. The operation in a MCB is thermal or thermal magnetic. On the other hand, MCCB has the same amount of rated current, but here, the trip characteristics can be adjusted when the ratings are high.

Common Trip Breakers: When branch circuit has to be supplied with more than a single live conductor, the live conductor must be protected by a breaker pole. So to ensure that the live conductors are interrupted in case of a pole tripping, this tripping method has to be used.

Medium Voltage: These are rated between 1 and 72 kV and can be assembled into switchgear line ups enclosed in metal for indoor domestic use. These could be connected to the circuit by bolted linkages to wires or bus bars specifically in outdoor switch yards.

High Voltage: These are used to protect and control electrical power transmission networks. Although the definition of 'high voltage' varies, yet in power transmission work, it is usually believed to be around 72500 V or higher. This is according to the International Electrotechnical Commission.

Fuses

This is basically a short for fusible link. This fusible link in electrical engineering terms is a kind of sacrificial over current device. Sacrificial, here, pertains to any part of a machine made and engineered with an intention to give away and fail under extreme mechanical stress or electrical stress in this case. This part fails first, thus bearing the brunt of the fault and saving the whole system. Now the basic part of this tool is a metal wire or a strip which is bound to melt in case of too much of a current flow. This disrupts or creates an obstacle in the circuit where it is connected. Now to protect the whole system and prevent the damage by fire or overheating, the fuse blows off. These are chosen to allow the passing of normal current and it cannot take excessive current for longer periods. This mechanism is necessary to avoid and cut down risks to human life and damage.

Operation
A fuse has a metal strip or wire element of a small cross section in comparison to the circuit conductors, which is mounted between a pair of electrical terminals. This is generally enclosed by a non-conducting and non-combustible casing. To carry all the current passing through the protected circuit, it is arranged in series. Now the element is determined for size and construction so that the heat produced considering normal current does not result in the heating of the element.

Types
There are many types of fuses - namely miniature and micro, British Domestic Fuses, Automotive, Blade type, SAE Fuses, Strip Fuses and high Voltage fuses. Just like the circuit breakers, these range from the lowest rating to the high voltage needed for electrical power transmission networks.

Comparing Circuit Breakers with Fuses

• For starters, fuses have an edge over circuit breakers, in which they are cheaper.
• When it comes to the mechanism, circuit breakers are more complicated than the fuses.
• Another important differentiating factor is that the fuse has to be totally replaced, whereas the circuit breaker just trips. In that case you just have to push it up.
• In some cases, Special current limiting fuses are preferred over molded case circuit breakers for the protection of the breakers in low voltage power circuits.
• Some types of circuit breakers have to be maintained periodically to ascertain their mechanical operation during an interruption. On the contrary, fuses do not need any periodical maintenance and mechanical operation for ensuring operation under faulty conditions.

One thing is pretty clear from the differentiation that, both are meant for safety of the electrical circuit or a network, and save it from major damages.