The RD series of residual current relays is designed for leakage current detection, protection and monitoring functions, when used in conjunction with an external toroidal transformer belonging to the TR family. It is composed by DIN-rail mounted RD2 and RD3 relays. ABB's Control Room offering includes a comprehensive range of solutions designed to optimize the operator workspace for critical 24/7 processes across various industries. The choice of toroidal transformers is made according to the useful diameter and the minimum value of the leakage current to be detected. RCD's are used in unison with a circuit pr ective device in industrial applications in the United States.