The earliest people will be on the AC called contactor, DC called relay, the reason is that the AC on the contactor body shape is relatively large, DC on the contactor is relatively small, and some of them are all called contactor;

Relay and contactor in the function there is no difference, are a control switch, early contactor application in the alternating current, due to the DC circuit design focus on the integration of miniaturised space, and research and development of a more compact contactor compression version in the DC low voltage, for the distinction called relay.

But with the social development of DC voltage and current enhancement, relays also enhance the high voltage relays, contactors are also miniaturised development, so that relays and contactors are difficult to distinguish between the industry and the country does not have a set of standard distinction, coupled with the relay derived from many different versions, such as time relay (set a certain time to automatically disconnect and connect), high temperature relays (detected at a certain temperature) (when a certain temperature is detected), and so on.