A modular building system arrangement includes a plurality of electrical building systems. Each electrical building system has a housing with a mechanical connector that is connectable with a like connector of each other building system housing. Members of any subset of the building system housings are connectable with each other to form a building system assembly. The building systems of the building system assembly conjointly define an electrically conductive pathway interconnecting each of the building systems of the building system assembly. The pathway carries power and/or data.