An electrical enclosure for use in poured concrete construction having a peripheral wall with opposed longitudinally extending walls longer than opposed laterally extending walls and at least one physical support located substantially midpoint along the opposed longitudinally extended walls to resist deflection of the opposed longitudinal walls caused by the hydraulic pressure of concrete poured around the enclosure. The physical support can be a crossbar extending across the opening of the electrical enclosure with the ends of the crossbar fixed to the longitudinally extending walls. The physical support can also be fastening sleeves extending along at least a portion of the width of the longitudinal walls for receiving elongated fasteners which extend into the concrete form thereby resisting deflection of the opposed longitudinally extending walls.