Front panel residual current relays are electronic devices used in combination with an external toroidal transformer. The choice of toroidal transformers is made according to the useful diameter and the minimum value of the leakage current to be detected.
The range of ELR front panel residual current relays has been tested in combination with miniature circuit breakers (S200 range) and moulded case circuit breakers (Tmax series up to T5 630 A) conforming with IEC/EN 60947-2 Annex M.