The increasing integration of renewable energy resources (e.g., photo-voltaic cells, wind farms) has turned traditional electric grids into smart ones. This evolution takes an active role in smart energy systems, especially when integrating a Wireless Sensor Network (WSN) to control and manage the grid. However, monitoring the whole grid with constrained devices is a challenge worth considering. In this paper, we introduce a WSN demonstrator for Smart Grids as part of the SoMel SoConnected project. It consists of Raspberry Pi and Zolertia ReMote sensor nodes deployed all over the building of the Catholic University of Lille and Yncréa Hauts de France. Thus, providing a WSN testbed in a real Smart Grid environment. A performance evaluation is conducted in the wired and wireless architectures in order to test some of the metrics that could be evaluated in this testbed, particularly the end to end delay and the packet delivery ratio.