What is Circuit Breaker ?

 A circuit breaker is a switching device which also offers protection against short circuit. Unlike a fuse, the circuit breaker does not blow off but trips whenever there is a fault. The circuit breaker complies with IEC 60947-2 & can offer protection up to 150KA even beyond that, also a circuit breaker can offer a no of protections such as against:

Overload

Short Circuit

Under Voltage

Neutral

Earth Fault

A circuit breaker is not required to be replaced after tripping once, instead it must complete its total no of operations as declared by the manufacturer. The tripping time for the circuit breaker may vary w.r.t its type, for example. the trip time for MCCB is less than 10ms & the opening time for ACB shall be less than 30ms. Not only this, but MCCB also has a dedicated position for tripping, whenever the MCCB trips, but its actuator lever also comes in between i.e. neither in ‘ON’ nor in ‘OFF’ position.

According to the medium of arc quenching, the circuit breaker can be differentiated as below

SNO	MEDIUM OF ARC QUENCHING	CIRCUIT BREAKER
1	AIR	ACB, MCCB
2	VACUUM	Vacuum Circuit Breaker
3	GAS	SF6 Circuit Breaker
4	OIL	Oil Circuit Breaker

method of tripping, the circuit breaker can be below types

SNO	METHOD OF TRIPPING	CIRCUIT BREAKER
1	BIMETAL (for Overload) & Armature (for Short Circuit)	Thermal Magnetic Type
2	ELECTRONIC	Microprocessor Type

differences between Fuse & Circuit Breaker

 

Basis for Comparison	FUSE	CIRCUIT BREAKER
MAINTENANCE	Fuse can only be used 1 time, it is a non- reusable device	Circuit Breaker can offer a total no of operations as declared by the manufacturer.
TRIP TIME	2-5ms, quickest operating device	Vary as per the device, ex: for ACB it can be 30ms & for MCCB can be less than 10ms
UTILIZATION CATEGORY	If the first letter is ‘g’ means both protection (O/L + S/C), If the first letter is ‘a’ only S/C will be there.	If category A it means no Icw shall be there, If category B, Icw shall be there
METHOD OF TRIPPING	‘SOLDER’ for Overload, ‘ELEMENT’ for Short Circuit	Available as ‘MICROPROCESSOR’ type & ‘THERMAL MAGNETIC’ type

What is Fuse ?

Fuse is a device that blows in case of a fault & can offer protection up to 80KA even beyond that. Whenever there is a fault in the system the fuse blows off & protects the system by cutting off the supply. A fuse is generally made of a ceramic body, having an element, The body is filled with quartz sand as shown in the fig:

Whenever there is an overload in the system, the solder as shown gets into a chemical reaction resulting in cutting off the supply. In the case of a short circuit, the element gets torn due to the application of high electrodynamic force on the same because of high current such as a short circuit. The blown fuse can be easily identified by the pop up indicator which pops up whenever the fuse interrupts. The function of quartz sand is to successfully quench the arc & absorb the pressure thus, not letting the fuse to explode. The fuse is the staunchest combatant of the system as it is the quickest interrupting device available in the entire electrical system. The fuse blown within 2-5ms hence saving the maximum amount of let-through energy.

Fuse can be identified as mentioned below:

The first letter is ‘a’ if the fuse is for short-circuit protection only; an associated device must provide overload protection.

The first letter is ‘g’ if the fuse is intended to operate even with currents as low as those that cause it to blow in one hour, ex. Overload. These are considered general-purpose fuses for the protection of wires.

The second letter indicates the type of equipment or system to be protected:

G – General purpose protection of wires and cables

M – Motors

PV – Solar photovoltaic arrays as per 60269-6

R, S – Rectifiers or semiconductors as per 60269-5

Tr – Transformers

Fuse although, is the most dependable & trusted protection device but can be used only one time, in no case the fuse can be repaired after it blows off it only needs to be replaced.