The increasing installation of decentralized energy converters merges networks of different energy carriers to a multi-carrier energy distribution network (MEDN). To operate MEDNs efficiently and safe, the state of the network
has to be monitored. An economically reasonable approach for monitoring MEDNs is provided by state estimation techniques, which however expect the network to be observable. To the best of our knowledge, we are the first to address the observability on MEDNs. Hence, we introduce a first graph-theoretic model serving as a starting point for introducing structural concepts, such as observability, for MEDNs.