Contactor Vs Relay
Answer : Wikipedia's Contactor article explains it pretty well. Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices . Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open ("form A") contacts . Unlike relays, contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents . [Emphasis mine.] Further down the same article ... Differences between a relay and a contactor: Contactors generally are spring loaded to prevent contact welding. Arc-suppression relays usually have NC contacts; contactors usually do not (when de-energerzied, there is no connection). Ma...