A contractor is an electromagnetic device which is used to make or break of an electrical circuit. there is two type of contractor.
- power contactor.
- auxiliary contactor.
Power contactor is used in power circuit like switch on/off of a motor capacitor. while auxiliary contactor is used to switch on or off of a control circuit. a power contactor have 3 main contacts while an auxiliary contactor has many contacts like 1no+1nc 2no+2nc ect..power contactor is generally used where we required to make and break a large current carrying circuit.
The Relay is similar to an auxiliary contactor which is used in general control circuit, especially in plc for as a digital input feedback or as a digital output to switch on or off an electrical contractor. we can also be used as a relay in place of an auxiliary contactor. relays are always used in a low current carrying circuits. it comes with a rating of 5–20 amps. while a power contactor generally comes with from 9 amps to 600 amps.