From the UL BXUV guide info
6. Metallic Electrical Outlet Boxes
Listed single and double gang metallic outlet and switch boxes with metallic or nonmetallic cover plates may be used in bearing and nonbearing wood stud and steel stud walls with ratings not exceeding 2 h. These walls shall have gypsum wallboard facings similar to those shown in Design Nos. U301, U411 and U425. The metallic outlet or switch boxes shall be securely fastened to the studs and the opening in the wallboard facing shall be cut so that the clearance between the box and the wallboard does not exceed 1/8 in. The surface area of individual metallic outlet or switch boxes shall not exceed 16 sq in. The aggregate surface area of the boxes shall not exceed 100 sq in. per 100 sq ft of wall surface.
Metallic boxes located on opposite sides of walls or partitions shall be separated by a minimum horizontal distance of 24 in. This minimum separation distance between metallic boxes may be reduced when Wall Opening Protective Materials (CLIV) are installed according to the requirements of their Classification.
Metallic boxes shall not be installed on opposite side of walls or partitions of staggered stud construction unless Wall Opening Protective Materials are installed with the metallic boxes in accordance with Classification requirements for the protective materials.
Roger
[This message has been edited by Roger (edited 07-16-2004).]
