Fuses and Circuit Breakers

Fuses and Circuit Breakers

Fuses and Circuit Breakers (CB) are used for the protection of power system. These along with other protective equipment like relays, isolater, switches, are collectively called as switchgear(switching equipment used in power systems).

The basic function is to break the circuit in case of faulty conditions so as to protect the power system equipment and auxiliaries.

FUSE is a low resistance device which is placed in the circuit for protection. Under faulty conditions when the current becomes more than the desired value, then due to the increase in temperature the fuse wire melts and breaks, thus breaking the circuit. These are used for lower power ratings and can be used only once, after that it has to be replaced with a new one.
CIRCUIT BREAKER also solves the same purpose i.e. it breaks the circuit when the fault occurs. These are used for large ratings and in the power systems and auxiliaries. CB also has the capability to re-close after the fault is through i.e. when the system gets healthy. The CB has two parts/contacts one is static and the other is moving(the one responsible for making or breaking the contacts).When the contacts of CB separate, then it said to have tripped. Tripping of the circuit breaker has to be very fast so as to avoid the arc formation between the two contacts, otherwise it will defeat the purpose of installing the CB. The trip signal is given to the CB by an other protective device called as an ELECTRICAL RELAY. CB’s are categorized on the basis of the power ratings and the medium used to extinguish the arc formed during the breaking of the contacts.

Small fuses used in the extension boards, UPS etc..

This type of fuse were used at homes untill late 90’s early 2000’s. now these have been kind of phased out because they are not reliable if you dont have back up to replace a fused fuse. These have been replaced by MCB’s(miniature circuit breakers).