A cover for an electrical rail mount device is provided. Further, an electrical rail mount device for mounting on a rail is provided, comprising at least ono input terminal configured to receive an input line, fixing means configured to fix the input line to the input terminal to establish an electrical connection, a lockable cover reversibly movable from an open state into a closed state, whereas the cover is configured to cover the fixing means in the closed state, such that the fixing means can only be accessed by moving the cover from the closed state into the open state, an electrical element arranged in the cover and configured to provide an electrical function to an active electronic element of the electrical rail mount device, wherein an electrical connection is provided between the electrical element and the active electronic element.