An electrical box assembly for providing a secure electrical enclosure on walls constructed with steel studs of two conventional sizes. The electrical box assembly includes an electrical box including captive fasteners on one sidewall and a bracket that is adjustable in length for attachment to the opposite sidewall. The adjustable length bracket may be used as is for bracing the opposite sidewall of the electrical box for a wide stud. A bend line is provided on the bracket for enabling simple reduction of its length for bracing the electrical box against a narrow stud. The electrical box assembly provides an electrical box that is fastened directly to a stud on one sidewall and braced against the drywall at both ends of the box on the opposite sidewall to securely hold the electrical box with respect to the wall.