The document provides an overview and user guide for the MK300 and MK300E earth leakage relays, which monitor electrical installation leakage currents. Key features include microprocessor-based design, digital filtering to minimize nuisance trips, continuous display of leakage current, recording of tripped current values, and programming of sensitivity and time delay settings. The MK300E adds remote test and reset inputs, a positive safety output contact, and 50% pre-fault contact. Technical specifications include voltage and current ratings, indicator functions, mounting details, and connection diagrams.