Re: How do circut breakers work?

There are basically two different kinds of circuit breakers:  magnetic and 
thermal.  

Magnetic circuit breakers are by far more common because they are 
indifferent to temperature variations and provide an accurate and 
consistent response.  The basic idea is that of an electro-magnet.  This is 
that the wire is wrapped around a steel core.  The strength of the 
electromagnet is proportional to how much electrical current is flowing 
through the wire.  So the more current, the stronger the magnetic field 
generated by the magnet.  At a certain point, the magnetic field will be 
strong enough to pull a metal switch sitting above it.  When this switch is 
pulled, the current shuts off and the switch locks in place until it is 
reset.  

Thermal circuit breakers use a bimetalic strip in series with the circuit.  
As electricity flows through the strip it gets warmer.  The two kinds of 
metal heat differently causing it to bend.  After it bends a given amount 
it trips a circuit which will shut off the flow of electrical current.