- This Interfacing Plug-In Relay Socket reflects Schneider Electric expertise in relay since 1924, by help to reduce the size of enclosures and at the same time increase machine reliability for industrial machines, packaging, textile, HVAC, automation control panels, low/medium voltage switchgear, motor Controls, PLC Interfaces, power supplies, Building or medical equipment, lighting Controls. It has large choice of number of contacts for high rated current use.