Relays and contactors are devices used to switch or interrupt the flow of electrical current in one or more circuits, using a control signal which is galvanically isolated from the circuit(s) being controlled, with various sub-groups demarcated along lines of device construction or intended application. Traditionally and still-commonly based on the use of an electromagnet to open or close a set of mechanical switch contacts, newer devices using solid-state technologies are also widely available, with both types having characteristics to reccomend them under different application conditions.