ISO cover for LV HRC base Size 1 LV HBC fuse system 3NA, 3ND for selective line and plant protection. As an important component of the SENTRON protective components for electronic installations, the LV HRC fuse system from Siemens provides effective protection for personnel, equipment and plants by means of a reliable shutdown function in the event of an overload or short-circuit. Higher short-circuit currents and better current limitation can be achieved than with miniature circuit breakers. Key features of…3, 4 and 4a.