Up through the 2015 Edition of NFPA 101, membrane penetrations in 1-hour or more rated walls/partitions allows any "steel electrical box not exceeding 0.1 sqft" to be addressed by several options.
The IBC has a similar provision, although it talks about 16-square-inch boxes instead of 0.1 sqft.
NFPA 101 2012
22.214.171.124.3 Where walls or partitions are required to have a minimum 1-hour fire resistance rating, recessed fixtures shall be installed in the wall or partition in such a manner that the required fire resistance is not reduced, unless one of the following is met:
(1) Any steel electrical box not exceeding 0.1 ft2 (0.01 m2) shall be permitted where the aggregate area of the openings
provided for the boxes does not exceed 0.7 ft2 (0.06 m2) in any 100 ft2 (9.3 m2) of wall area, and, where outlet boxes are installed on opposite sides of the wall, the boxes shall be separated by one of the following:
(a) Horizontal distance of not less than 24 in. (610 mm)
(b) Horizontal distance of not less than the depth of the wall cavity, where the wall cavity is filled with cellulose loose-fill, rock wool, or slag wool insulation
(d) Other listed materials and methods
The 0.1 sqft threshold seems overly vague - a 4-inch x 4-inch electrical backbox, for instance, is 16 square inches while 0.1 sqft = 14.4 square inches.
Has anyone come across this part of NFPA 101 before and addressed this issue with anything other than a listed box or puddy pad? My understanding is that the only way to address these 4x4 boxes, since they don't qualify as being 0.1 sqft or less, is to have a listed electrical outlet box or to use a listed assembly around the box (like a puddy pad).
After looking into this question a little more, it looks like the 2018 Edition of NFPA 101 even clarified this section to change 0.1 sqft to 16 square inches, but we're not under the 2018 Edition for this project.
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6/25/2019 06:13:45 am
The 2018 version of NFPA 101 did clarify this. Essentially I've come across three practical options with 101 and IBC, which includes using a backbox which is (1) tested/listed for use in fire-resistive construction, (2) separated by 24 inches minimum, or (3) installed with puddy pads on both back-to-back electrical boxes.
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