All nonmetallic outlet and switch boxes intended for use in fire-resistant rated assemblies must be specifically investigated for use in such assemblies, and are required to be marked as follows:

• The certification mark located in the base of the box

• Class * hr, where * indicates the hourly rating (i.e. 1 hr or 2 hr)

• F, W, and/or C, where F = Floor, W = Wall, and C = Ceiling

These nonmetallic boxes are Classified for use in certain fire-resistive designs when installed in accordance with the details prescribed for each Classified product.

The information for each Classification includes:

• The model numbers for the Classified products

• A description of the fire-resistant rated assemblies

• The spacing limitations for the boxes

• Installation details