The understanding of incumbents' behaviour in sustainability transitions in the energy sector is gaining increasing scholarly attention. However, two key structural characteristics of many incumbents in the energy sector are hardly taken into account: they are mostly public companies and they are operating in infrastructure network industries. Furthermore, studies on incumbents in the energy sector do not consider the multi-scalar situation of federal energy governance systems, as in Germany and Switzerland. This paper presents six analytical categories, which reveal the specifics of public energy companies and provide categories for a more precise analysis. They are developed through an iterative theory building process, combining empirical evidence from urban utility companies in Germany and Switzerland and theoretical insights from public corporate governance and network industries literature. Finally, the paper discusses, how these categories can be linked to the triple embeddedness framework (Geels, 2014) and transferred to other infrastructure sectors (e.g. the telecommunication or the railway sector) to enrich the understanding of public incumbents in sustainability transitions.