Electrical and Automation Engineer . Specialized in LV Switchgear Design and process automation
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Circuit breakers and fuses, in spite of performing a common task of interruption of the flow of fault current to an equipment or system, are entirely different from each other in all aspects of construction and principle of operation. Whenever a short circuit or an overload occurs, heavy fault current flows through the equipment that may damage the equipment and may cause interruption of service. Here arises the need for the protection devices such as fuses, relays, circuit breakers etc. The main function of these devices is to interrupt the flow of fault current to an equipment and protecting it from severe damage. Few people think that the circuit breakers and the fuses are the same. But it is not. This article will make you clear “what is a circuit breaker?” “What is an electric fuse?” and the difference between them.
A circuit breaker is a mechanical device used to perform switching operations in an electrical circuit under normal as well as abnormal conditions. When a circuit breaker is employed in the protection of an electrical circuit, they are equipped with a trip coil connected to a relay arrangement, which is designed to sense the abnormal conditions and close the breaker trip circuit. Therefore an additional relay arrangement is always required for the automated operation of a circuit breaker. For breakers of very small capacity, for example, low voltage circuit breakers up to 100A, have thermal couple arrangement instead of fault sensing relays.
Operating principle of Circuit breakers
The simplified operating principle of a circuit breaker is as follows: A circuit breaker consists of a fixed contact and a moving contact. Under normal conditions, these contacts will be closed allowing current to flow through it. When an abnormal condition is sensed by the relay arrangement provided, it energizes the trip coils and pulls back the moving contact apart and opens the circuit breaker, thereby interrupting the flow of current. The circuit breaker is reset manually or automatically after the clearance of fault. Circuit breakers can also be operated manually.
A model of circuit breaker relay arrangement
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Read More about fuse
- Electric Fuse
Electrical fuse is a simple, less resistive, self sacrificial and cheapest device used to interrupt a circuit under short circuit, excessive overload or over current conditions.
- Rewirable fuses (Electric)
Rewirable fuse is also known as kitkat fuse, is a simple reusable fuse used in homes, offices and in the protection of outdoor distribution transformers. It is available in a wide range of ratings.
- High Rupturing Capacity ( HRC) Fuses
High rupturing capacity (HRC) fuses are totally enclosed fuses with definite known- high breaking capacity which have been developed after intensive research by manufacturers and supply engineers.
Fuse is also a protection device that is entirely different in construction as well as in operation from the circuit breakers. A fuse consists of a fusing element held between two metal contacts. It is connected in before and in series to the equipment or the circuit to be protected. It is the simplest and the cheapest protection device and does not require any additional relay arrangements.
Operating principle of fuses
An electric fuse works on the principle of heating effect of the electric current. When the current flowing through the fuse element is within the limits, the heat developed on the fuse element will be completely dissipated to the surrounding air. During the occurrence of fault, the current flowing through the fuse element increases rapidly and the heat generated cannot be dissipated so fast and thus the fuse element melts and breaks the circuit. Fuse once blown out cannot be reused. Rewirable fuse can be reused after replacing the blown out fuse element with a new one.
Difference between fuse and circuit breakers
Comparison between fuse and circuit breakers
|S. No.||Particulars||Fuse||Circuit breakers|
Fuse is used for the detection of fault as well as the interruption of circuit.
Circuit breakers perform switching operations (make and break operations) alone. Fault detection is made by protective relays.
Principle of operation
The operation of electric fuses is based on the heating property of electric current.
Operation is based on common switching principle.
Mode of operation
Manual operation. To make circuit breakers automatic, additional relay arrangements should be made.
Additional equipments required
No additional equipments are needed.
For automated operations additional relay arrangements should be needed.
Operating time of fuses is very small, close to 0.002 seconds.
Operating time of circuit breakers are more than that of the fuses. ( 0.02 -0.05 seconds)
Breaking capacity of fuses is small.
Breaking capacity of circuit breaker is large.
All other types of fuses except rewirable fuses are non reusable. Rewirable fuse can be reused after replacing the burnt out fuse element with a new one.
Circuit breakers can be reused.
Very high compared to that of the fuse.
Where to be used?
Fuses can be used in the protection of low voltage circuits. For the protection of high voltage circuits, say 33kV and above, Circuit breakers are employed. Circuit breakers are mostly preferred where the chances for the occurrence of fault are more. Fuses are commonly employed in the protection of cables in low voltage lights, power circuits, in transformers having rating not more than 200kVA and in small electronic circuits.
Test your knowledge!
For each question, choose the best answer. The answer key is below.
- Which of the following protective device is used in your refrigerator?
- Circuit Breaker
Spree on August 06, 2018:
Accurate informative and to the point
OSBERT JOEL C (author) from CHENNAI on February 07, 2015:
Thank you Jane Ramona Rynkiewicz Frieman..
Jane Ramona Rynkiewicz Frieman from Morris County, New Jersey on February 06, 2015:
This is a well written and informative article about fuses and circuit breakers. My brain is "wired" for creativity though.