Outlets in Fire-Rated Walls
One thing for electrical and RCDD designers to look out for are outlets located in fire-rated walls. Generally, you find fire-rated walls around stairwells, elevators and elevator equipment rooms, and they also separate sections of a building that are different occupancy ratings. To know for sure, one should reference the Life Safety Plans usually issued by the architect.
For electrical and low-voltage outlets located in fire-rated walls, some sort of fire-rating material needs to be added to the back of the box to maintain the integrity of the wall. Fortunately, Underwriters Laboratory (UL) certifies products for what it calls “membrane penetrations” of fire-resistance rated wall assemblies. There are three types of material technologies: putty pads, insert pads, and gaskets. From a UL publication on the subject:
Putty pads are putty like products installed on the outer surfaces of an electrical box prior to installation in the gypsum board membrane on the wall. Insert pads are for installation on the inside back surface of the box. Finally, gaskets are for installation under the cover plate of the box. These later two products may be installed after the gypsum membrane is in place. Each of these products are Classified for use in specific types of fire resistive designs when installed in accordance with the details provided in each Classification.
To find available manufacturers and products, you can search the UL database.
Search for QCSN under UL Category Code.
More from the UL publication:
The information in each Classification includes
1. the model numbers covered,
2. the type and size of electrical box covered,
3. a description of the fire-resistance rated wall assemblies covered,
4. the specific method for the installation of the product,
5. the type of cover plate covered, and
6. the required spacing between boxes on opposite sides of the wall.
As practical and informed designers, we can make sure we specify these products in the appropriate section, require these outlet locations be shown and identified on the shop drawings, and make site observations during construction to double-check their installation.