EXPLICACIONES SUCESIVAS:

Framed steel and wood stud wall assemblies are often used to conceal electrical cables and raceways. At those locations where the electrical service penetrates the fire- rated membrane for the stud wall assembly, fire stops must be provided. Typical

arrangements of electrical wiring in conduit at penetrations of a stud wall assembly are shown in Figure 9.J.

Figure 9.J:

Examples of combustible and noncombustible conduit

installations for electrical service penetrations through a stud wall

If Acoustical Separation is Required…

The complete separating wall construction (including treatment of all penetrations) should provide the required STC.

Note: For separation between service spaces (such as adjacent electrical rooms, or above a ceiling) the NBCC has no STC requirement.

Best Practice for Fire Stops for Electrical Service Penetrations 9-14

Examples of electrical service penetrations without conduit are illustrated in Figure 9.K. Where sleeves are used to pass wires through a stud wall assembly, fire stops are required for the space between the sleeve and the wall assembly and for the space where the cables enter and exit the sleeve as shown in the lower figure. Specific details for these fire stop systems can be found in the manufacturers' technical literature.

Figure 9.K:

Examples of electrical cable without conduit, at penetrations through a stud wall assembly.

If Acoustical Separation is Required…

The complete separating wall construction (including the fire stop system at any penetration through the assembly) should provide the required STC. Note: For separation between service spaces (such as electrical rooms or above a ceiling) the NBCC has no STC requirement. See Section 2.7.

Electrical Panels – Electrical panels normally are not located in a stud wall assembly fire separation, in part because their size makes it difficult to provide

appropriate fire stops. Rather, electrical panels can be located in a non-fire-rated wall assembly and then no fire stops are required; or they can be located in a furred-out wall assembly located adjacent to a fire separation as shown in Figure 9.L which would also not require fire stops. The locations where cables from the electrical panel penetrate the fire-rated membrane still require fire stops. Another possible option would be to frame and install a gypsum board enclosure around the opening in the fire-rated wall assembly to create a recessed cavity for the electrical panel. This latter arrangement has been accepted by some authorities as providing equivalent protection.

Figure 9.L:

Example of electrical panel opening in framed furred- out wall assembly

If Acoustical Separation is Required…

The complete separating wall construction (including the fire stop system at any penetration through the assembly) should provide the required STC. Rated wall assembly with no penetrations is one example of good practice to achieve required STC separation between side-by-side units.

Sealed cable penetrations through gypsum board behind the electrical panel will not reduce STC of

Best Practice for Fire Stops for Electrical Service Penetrations 9-16

Electrical Outlet Boxes – The NBCC is unclear as to the extent to which electrical boxes need to be protected or offset to ensure that the integrity of the fire separation is maintained [Ref: NBCC Sentence 3.1.9.3.(6)] As a reasonable position to achieve the necessary integrity, electrical outlet boxes should be installed in fire-rated stud wall assemblies so that there is at least one full stud space between boxes on opposite faces of the assembly. Listed fire stop systems for the boxes on both faces should be utilized. As illustrated in Figure 9.M, the electrical boxes on both sides of the wall assembly need to be provided with fire stops. Figure 9.M shows an arrangement of a double stud wall assembly with greater than one stud space spacing between electrical outlet boxes. For a single stud wall in the lower portion of the figure, the electrical outlet boxes can be in adjacent stud spaces since each stud space is essentially a cavity sealed by framing on four sides. See discussion in Section 9.3 where fire stops may not be required in some assemblies.

Figure 9.M:

Examples of electrical boxes located at least 1 stud space apart in stud wall assemblies. The upper figure shows a double stud wall assembly, and the lower shows a single stud assembly.

If Acoustical Separation is Required…

The complete separating wall construction (including the fire stop system at any penetration through the assembly) should provide the required STC. Note: No sound rating is needed for a fire stop system that penetrates only one surface of an insulated cavity construction. See Section 2.7. The effect of such penetrations on STC is negligible if wall cavities are filled with fibrous absorptive material and fire resistance requirements are satisfied as illustrated.

If there is less than one full stud space between electrical boxes as shown in Figure 9.N, additional protection for the penetration is required. Figure 9.N illustrates one arrangement in which electrical outlet boxes can be installed where there is less

than one full stud space between boxes. In this case, the box on one side of the double stud wall is enclosed by a horizontal fire block cross brace and gypsum board to isolate it from the box on the opposite side of the wall. In this arrangement, fire stops are required where the electrical cable penetrates the fire block cross brace and for the electrical box on the opposite side of the wall. The listed fire stop system should be installed in accordance with the manufacturers' technical literature.

Best Practice for Fire Stops for Electrical Service Penetrations 9-18