19-07-2012, 11:39 AM
L.T Circuit Breakers
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L.T Circuit Breaker
A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.
Basic Principle:
When a current supplies enough energy to operate a trigger device in a breaker, a pair of contacts conducting the current are separated by preloaded springs or some similar mechanism.
Thermal Circuit Breakers:
In this device, the current flows from the battery terminal, through the bi-metal strip and then to the other terminal. The bi-metal strip is made of two different types of metal which have different coefficients of expansion. This means that one will expand more than the other when the rise in temperature is the same for both pieces. The two metals are bonded to each other. When the strip heats up from the current flow through it, one type of metal expands more than the other.
Circuit Breaker can be divided into two categories:
The circuit beaker that trips or breaks the circuit when there is a short circuit or when there is too large current through the circuit.
The circuit beaker that trips or breaks the circuit when there is small leakage currents from the live wire to the earth wire.
Miniature circuit breakers (MCBs) :
Miniature circuit breakers are similar to moulded case circuit breaker but as their name implies, these are smaller in size and are mostly used for current ratings below 100A. These are normally available in single pole (SP), single pole neutral (SPN), double pole (DP), triple pole (TP), triple pole neutral (TPN), and four pole versions (FP).