An adapter closure structure for electrical conduit systems of the type having conduit bodies, for which additional conduit access to an in-service conduit junction box can be provided without the need for removing and/or rewiring the in-service junction box. In a first embodiment, a structure is provided in the form of a closure plate having one or more conduit hubs to replace a flat closure plate on one side of a conduit body. In a second embodiment, a second conduit body may be joined to the in-service body utilizing a novel coupling ring. In this alternative embodiment, the second body can provide additional interior working space. In addition the second body may also optionally add one or several additional conduit hubs for added access to the in-service system. In both embodiments, the closure structure is fitted into a female opening of the conduit body for structural integrity.