A beam-fixing member for mounting an electrical installation box on a support, said beam-fixing member comprising: - a first mating surface to removably attach with said electrical installation box, and - a second mating surface fixedly attachable with the support, said first mating surface and second mating surface are joined by a connecting member, wherein said first mating surface comprises: - lug members, extending from said first mating surface to attach fixedly with a mating portion of said electrical installation box; - at least a hook member, disposed along an edge of said first mating surface to removably attach with said electrical installation box; - a joining edge of said first mating surface and said connecting member, configured to removably attach said beam-fixing member with corresponding edge of said electrical installation box; and - at least one deflection-arrest member, protruding outwardly perpendicular to the first mating surface of said beam-fixing member and adapted to be placed in contact with the support to support said installation box against external forces, and wherein said second mating surface comprises self-nailing members for fixation of said installation box on the surface, said self-nailing member being arrow head shaped for easy penetration into the support, wherein the connecting member has an L-shape shape having a first surface from which the second mating surface extends perpendicularly and a second surface from which the first mating surface extends perpendicularly, and whereby the joining edge of said first mating surface and said connecting member is provided with at least a hole defining screw relief portion at the joining edge and mounting holes with linear snaps disposed therein to removably attach with the electrical installation box. - a first mating surface to removably attach with said electrical installation box, and - a second mating surface fixedly attachable with the support, said first mating surface and second mating surface are joined by a connecting member, wherein said first mating surface comprises: - lug members, extending from said first mating surface to attach fixedly with a mating portion of said electrical installation box; - at least a hook member, disposed along an edge of said first mating surface to removably attach with said electrical installation box; - a joining edge of said first mating surface and said connecting member, configured to removably attach said beam-fixing member with corresponding edge of said electrical installation box; and - at least one deflection-arrest member, protruding outwardly perpendicular to the first mating surface of said beam-fixing member and adapted to be placed in contact with the support to support said installation box against external forces, and wherein said second mating surface comprises self-nailing members for fixation of said installation box on the surface, said self-nailing member being arrow head shaped for easy penetration into the support, wherein the connecting member has an L-shape shape having a first surface from which the second mating surface extends perpendicularly and a second surface from which the first mating surface extends perpendicularly, and whereby the joining edge of said first mating surface and said connecting member is provided with at least a hole defining screw relief portion at the joining edge and mounting holes with linear snaps disposed therein to removably attach with the electrical installation box. and wherein said second mating surface comprises self-nailing members for fixation of said installation box on the surface, said self-nailing member being arrow head shaped for easy penetration into the support, wherein the connecting member has an L-shape shape having a first surface from which the second mating surface extends perpendicularly and a second surface from which the first mating surface extends perpendicularly, and whereby the joining edge of said first mating surface and said connecting member is provided with at least a hole defining screw relief portion at the joining edge and mounting holes with linear snaps disposed therein to removably attach with the electrical installation box.