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
