Diagnosing switching devices Contactor with remaining lifetime signal RLT A contactor's main contacts are wearing parts. The electrical life expectancy of the contacts is determined by the load to which they are subjected, the operating mode and the utilization category. Via the RLT function, the actual progress of contact erosion of each main contact is recorded, analyzed and stored, and signaled when specific defined limits are reached. Advantages of SIRIUS contactors with RTL Status-oriented maintenance enables optimum utilization of the contact material, allowing the contactor to be used for a longer period of time before a contact change is needed A reduction in downtimes, increased plant availability On-site visual checks are unnecessary A reduction in operating costs Stored RTL data are retained, even should the control supply voltage fail A warning is issued when the remaining lifetime reaches 20% The message indicating a remaining lifetime of 20% is sent via relay contact or AS-Interface. The messages reach the SIMATIC Maintenance Station e.g. over a digital input from SIMOCODE pro, and thus over PROFIBUS.