jdrummond
Member
- Location
- Portland, OR, USA
How can you pass cables through a fire-rated wall and keep "free air" ampacities?
I have a set of cables in free air that I need to pass through an 8-inch cinder block fire-rated wall and then in free air back to the transformer. I would like to use the "free air" ampacity ratings from Table 310.15(B)(17). Is there anyway to pass through a free-rated wall and keep the "free air" ampacity ratings?
1. One approach is to transfer the cables to a cable tray, in a single layer with over a diameter space between per 392.80(A)(2)(c). Then use a cable tray wall penetration sleeve with fire stop blocks. However, the cables will no longer be in free air for the 8 inches it is encapsulated by the fire stop material. So I can increase the size of conductors to get a necessary ampacity. Are there any exceptions for small lengths of "free air" cables not being in free air for small lengths (such as 8" out of a 50 ft run)?
2. Another option is to mount a fire-proof splice box of some sort at the wall. Attach cables to terminals on either side of the wall. Are there products that are designed for passing through fire-rated walls? Possibly use a wall penetration bus duct with cable terminals on each side.
I am curious if anyone has any creative ideas.
I have a set of cables in free air that I need to pass through an 8-inch cinder block fire-rated wall and then in free air back to the transformer. I would like to use the "free air" ampacity ratings from Table 310.15(B)(17). Is there anyway to pass through a free-rated wall and keep the "free air" ampacity ratings?
1. One approach is to transfer the cables to a cable tray, in a single layer with over a diameter space between per 392.80(A)(2)(c). Then use a cable tray wall penetration sleeve with fire stop blocks. However, the cables will no longer be in free air for the 8 inches it is encapsulated by the fire stop material. So I can increase the size of conductors to get a necessary ampacity. Are there any exceptions for small lengths of "free air" cables not being in free air for small lengths (such as 8" out of a 50 ft run)?
2. Another option is to mount a fire-proof splice box of some sort at the wall. Attach cables to terminals on either side of the wall. Are there products that are designed for passing through fire-rated walls? Possibly use a wall penetration bus duct with cable terminals on each side.
I am curious if anyone has any creative ideas.
