L.T Circuit Breaker

L.T Circuit L.T Circuit BreakersBreakers

L.T Circuit BreakerL.T Circuit Breaker

A A circuit breakercircuit breaker is an automatically- is an automatically-operated electrical switch designed to operated electrical switch designed to protect an electrical circuit from damage protect an electrical circuit from damage caused by caused by overloadoverload or or short circuitshort circuit. Unlike . Unlike a fuse, which operates once and then has a fuse, which operates once and then has to be replaced, a circuit breaker can be to be replaced, a circuit breaker can be reset (either manually or automatically) to reset (either manually or automatically) to resume normal operation. resume normal operation.


Basic Principle:Basic Principle:

When a current supplies enough energy to When a current supplies enough energy to operate a trigger device in a breaker, a operate a trigger device in a breaker, a pair of contacts conducting the current are pair of contacts conducting the current are separated by preloaded springs or some separated by preloaded springs or some similar mechanism. similar mechanism.


Because it is usual for an electric arc to Because it is usual for an electric arc to form between the contacts when a breaker form between the contacts when a breaker opens, some means must be provided for opens, some means must be provided for preventing rapid erosion of the contacts. preventing rapid erosion of the contacts.


Electrical systems in residential, Electrical systems in residential, commercial and industrial applications commercial and industrial applications usually include a panelboard for receiving usually include a panelboard for receiving electrical power from a utility source. The electrical power from a utility source. The electrical power is then delivered from the electrical power is then delivered from the panelboard to designated branch circuits panelboard to designated branch circuits supplying one or more loads. supplying one or more loads.


Thermal Circuit Breakers: Thermal Circuit Breakers: In this device, the current flows from the battery In this device, the current flows from the battery terminal, through the bi-metal strip and then to terminal, through the bi-metal strip and then to the other terminal. The bi-metal strip is made of the other terminal. The bi-metal strip is made of two different types of metal which have different two different types of metal which have different coefficients of expansion. This means that one coefficients of expansion. This means that one will expand more than the other when the rise in will expand more than the other when the rise in temperature is the same for both pieces. The two temperature is the same for both pieces. The two metals are bonded to each other. When the strip metals are bonded to each other. When the strip heats up from the current flow through it, one heats up from the current flow through it, one type of metal expands more than the other.type of metal expands more than the other.


When the temperature reaches a given When the temperature reaches a given point, the piece will snap into the open point, the piece will snap into the open position and the current flow will stop. position and the current flow will stop.


Magnetic Circuit Breakers:Magnetic Circuit Breakers: Some circuit breakers use a magnetic actuator to trip Some circuit breakers use a magnetic actuator to trip the circuit. In this type of breaker, the current flow the circuit. In this type of breaker, the current flow through the electrical device passes through an through the electrical device passes through an electromagnetic actuator. When the current flow electromagnetic actuator. When the current flow reaches a preset level (determined by the current reaches a preset level (determined by the current rating of the breaker), the magnetic field in the rating of the breaker), the magnetic field in the electromagnet is strong enough to trip the breaker electromagnet is strong enough to trip the breaker and allow the contacts to open. This type of breaker and allow the contacts to open. This type of breaker generally has to be manually reset. A well designed generally has to be manually reset. A well designed 'magnetically' actuated circuit breaker can operate 'magnetically' actuated circuit breaker can operate very quickly (possibly as fast as or faster than a fuse very quickly (possibly as fast as or faster than a fuse of equal current rating). of equal current rating).


Circuit Breaker can be divided into two Circuit Breaker can be divided into two categories:categories:

The circuit beaker that trips or breaks the The circuit beaker that trips or breaks the circuit when there is a short circuit or circuit when there is a short circuit or

when there is too large current through the when there is too large current through the circuit. circuit.

The circuit beaker that trips or breaks the The circuit beaker that trips or breaks the circuit when there is small leakage circuit when there is small leakage

currents currents from the live wire to the earth wire. from the live wire to the earth wire.

L.T Circuit BreakerL.T Circuit BreakerTypes of first Category:Types of first Category:Low voltage (less than 1000 V AC) types are common in Low voltage (less than 1000 V AC) types are common in domestic, commercial and industrial application, include:domestic, commercial and industrial application, include:

MCB (Miniature Circuit Breaker)—MCB (Miniature Circuit Breaker)—rated current rated current not not more than 100 A. Trip characteristics normally not more than 100 A. Trip characteristics normally not

adjustable. Thermal or thermal-magnetic adjustable. Thermal or thermal-magnetic operation. operation. MCCB (Moulded Case Circuit Breaker)—MCCB (Moulded Case Circuit Breaker)—rated rated current up to 1000 A. Thermal or thermal-current up to 1000 A. Thermal or thermal-magnetic magnetic operation. Trip current may be adjustable operation. Trip current may be adjustable in larger in larger ratings. ratings.


Miniature circuit breakers (MCBs) :Miniature circuit breakers (MCBs) :

Circuit breakers used in residential and Circuit breakers used in residential and light commercial applications are light commercial applications are commonly referred to as miniature circuit commonly referred to as miniature circuit breakers because of their limited size. breakers because of their limited size.


Miniature circuit breakers (MCBs) :Miniature circuit breakers (MCBs) : Miniature circuit breakers are similar to Miniature circuit breakers are similar to moulded case circuit breaker but as their moulded case circuit breaker but as their name implies, these are smaller in size name implies, these are smaller in size and are mostly used for current ratings and are mostly used for current ratings below 100A. These are normally available below 100A. These are normally available in single pole (SP), single pole neutral in single pole (SP), single pole neutral (SPN), double pole (DP), triple pole (TP), (SPN), double pole (DP), triple pole (TP), triple pole neutral (TPN), and four pole triple pole neutral (TPN), and four pole versions (FP). versions (FP).


Miniature circuit breakers (MCBs) are Miniature circuit breakers (MCBs) are fitted in consumer units in place of fitted in consumer units in place of fuses. They have the advantage that fuses. They have the advantage that they can be manually reset without they can be manually reset without having to replace wire as in the case of having to replace wire as in the case of the traditional fuse. The MCBs have the traditional fuse. The MCBs have either a button or lever that can be either a button or lever that can be flicked to reset it.flicked to reset it.


Moulded Case circuit Breakers:Moulded Case circuit Breakers:

Moulded case circuit breakers are power Moulded case circuit breakers are power switches and they all consist of five main parts.switches and they all consist of five main parts.

Moulded case (frame)Moulded case (frame) Operating mechanismOperating mechanism Contacts and extinguishersContacts and extinguishers Tripping elementsTripping elements Terminal connectionsTerminal connections


Moulded Case:Moulded Case: This is external cover of MCCB This is external cover of MCCB which houses all the components and is which houses all the components and is moulded from resin/glass-fiber material. It moulded from resin/glass-fiber material. It provides insulation between the live and provides insulation between the live and components and the operators.components and the operators.

Operating switch/mechanism:Operating switch/mechanism: This is a handle This is a handle which connects the internal mechanism for which connects the internal mechanism for ON/OFF/RESET operations.ON/OFF/RESET operations.


Contacts and extinguishers:Contacts and extinguishers: A pair of contacts A pair of contacts comprises a moving contacts and a fixed comprises a moving contacts and a fixed contacts. The instant of opening and closing contacts. The instant of opening and closing impose the most severe duty.impose the most severe duty.

Tripping elements:Tripping elements: The function of the trip The function of the trip elements is to detect the overload or short-circuit elements is to detect the overload or short-circuit condition and trip the operating mechanism.condition and trip the operating mechanism.

Thermal connections:Thermal connections: These connect the the These connect the the MCCB to a power source and a loadMCCB to a power source and a load

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L.T Circuit Breaker

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