Phoenix Contact PLC-RCS Relays. The range of compact PLC relays from Phoenix Contact give you a great choice of easy connection technology. The electromechanical relays act as the interface between your automation equipment and system peripherals. Features and Benefits. Saves space on the DIN rail Cost effective use the same electromechanical relay module design for both AC and DC switching voltage DIN rail mounting SPNO and SPDT models available. Typical Applications. The PLC relays are used in many different applications not limited to power amplication, electrical isolation or for using for voltage adjustment of frequency varying voltage levels.