differnce between circuit breaker & contactor

A circuit breaker is a switch that opens when too much current flows through it.

A contactor is a switch that opens or closes due to the presence/absence of a voltage across its coil. Similar to a relay

Al

I'm not sure but as a safty issue, isn't a CB latched in and on loss of power would need to be manually opened before restoring? and a contact is held in place with a coil which opens on loss of power? I dont think that all CB's are locked in, but if you are operating or in charge of any plant you would need to know. This in addition to the normal protection relays which have a separated control supply.

No, unless a CB is specifically modified to include what is called an "under voltage release coil", it will NOT open on loss of power. Standard CBs do not include a UVR, that is considered a special option or add-on.

Circuit breakers protect.

Contactors control.

The functions are NOT interchangeable. Circuit breakers are NOT designed for constant switching duty, they are typically designed to operate 10,000 times maximum, maybe less. Contactors are designed to operate 1,000,000 times MINIMUM, but do NOT posses any protection features in and of themselves.

Contactors and Circuit Breakers are functionally different.

Contactors are electromagnetic relays. Two pairs of contacts are operated by an electromagnet (magnetised with the switching 'on' of electromagnetic coil)to "on" position by the magnetic attraction and when the electromagnet is demagnetised the switch is brought back to off position with the help of mechanical springs when the electromagnetic coil is de energised.Contractors are used in power and control circuits of electrical systems.

Circuit Breakers are switching device with built in protection devices for Over current ,earth fault and optionally with undervoltage protection. There are various circuit breakers depending on their range of rated current capacity and voltage.

Miniature Circuit Breakers( MCB), Mould Case Circuit Breakers (MCCB) , Oil Circuit Breakers ( OCB) ,Minimum Oil Circuit breakers ( MOCB) , SF6 Circuit Breakers , Vacuum Circuit Breakers (VCB)