We are installing outlets in a 2 hour fire wall (U301). As I understand the UL standards, the total opennings in each 100 sq feet of wall space can not exceed 100 sq inches. Do only the boxes that exceed this figure have to be protected, or once you go over 100 sq inches do all the boxes in that area have to be protected?
UL listing card QCIT lists metallic outlet boxes for use in wood stud and steel walls not exceeding a two-hour fire rating. In general terms each box should not have more than 16 sq inches surface area and not more than 100sq. “ per 100 sq ‘. The box should be secure to stud and wall with not more than 1/8” clearance.
Plastic boxes are marked with their fire rating usually on the inside corner. Each Mfg has different installation instructions and you must refer to Manufactures instructions or the listing instructions in the UL Green Product Dictionary.
Hope this helps
Charlie P
The 100 in 100 is a maximum allowed openings before the wall would be compromised. If the wall will have metal boxes larger than 16 square inches, every one of the large ones would have to be protected with putty pack or boxed in with fire rated GWB. OR, if there were more than 100 square inches of accumulated area of metal boxes in any 100 square foot of wall, then you would have to putty pack or box in those boxes in excess of 100 square inches. Last, if you had to place metal boxes back to back within 24 inches, then you would have to putty pack one of them.
Go this web site and search for the QCIT listing. there is an article on on pdf with an over view for metallic and nonmetallic enclosures installed in fire rated assemblies
http://www.ul.com/.
Here's a 2002 NEC reference that seems to cover the subject:
300.21
FPN: Directories of electrical construction materials published by qualified testing laboratories contain many listing installation restrictions necessary to maintain the fire-resistive rating of assemblies where penetrations or openings are made.
Building codes also contain restrictions on membrane penetrations on opposite sides of a fire-resistance–rated wall assembly.
An example is the 600-mm (24-in.) minimum horizontal separation that usually applies between boxes installed on opposite sides of the wall.
Assistance in complying with 300.21 can be found in building codes, fire resistance directories, and product listings.
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).]
One last comment: You must follow the putty pack manufacturer's instructions. If they want putty on both boxes, then you gotta do it.