The XRI relay-interface board allows external switches and current consumers to be connected and can also be used for controlling external machines. The module board provides a maximum of 24 optically isolated inputs with minimal input current plus the same number of solid-state relay outputs that can handle AC or DC current. All inputs and outputs share a common reference potential, which is galvanically isolated from all other NEXUS components and the inputs or outputs. The XRI also offers the possibility of creating entirely potential-free contacts by combining adjacent ports. This halves the number of available channels, i.e. two contacts with common potential become one potential-free contact. This configuration can be selected via jumpers per contact pair. The output function can be controlled from the corresponding inputs or by the system software. Furthermore, the inputs may be used for controlling routing functions on the NEXUS system such as setting crosspoints.