A power transfer device adapted for interconnection with the electrical system of a building includes a cabinet, a set of switches mounted to an upper panel of the cabinet, and wires adapted to connect the switches to an electrical distribution panel associated with a building electrical system. The power transfer device includes an upper compartment and a lower compartment partitioned from one another by an intermediate wall. The upper panel closes the upper compartment and a lower panel is adapted to selectively close the lower compartment. A strain relief member is mounted in the lower compartment and tightly holds the wires against the housing to prevent the unintentional disconnection of the wires from the switches.