2 hour protection vs 2 hour assembly, wiring methods

[bubbarhd]

How is 2 hour protection defined? How is 2 hour assembly defined? Are they the same?
I have low volt wire runs for smoke control that require 2 hour protection. Is a wire run inside a 2 hour assembly considered 2 hour protected? Technically it's in the middle of a 2 hour wall, say a stairwell wall. But as I understand it, being in the middle means it is only 1 hour protected from fire from either side. Is the code calling for 4 layers of drywall all the way around my wires to obtain 2 hour protection or CIC rated wire?

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[JFletcher]

Welcome to the forum

How is 2 hour protection defined? How is 2 hour assembly defined? Are they the same?
I have low volt wire runs for smoke control that require 2 hour protection. Is a wire run inside a 2 hour assembly considered 2 hour protected? Technically it's in the middle of a 2 hour wall, say a stairwell wall. But as I understand it, being in the middle means it is only 1 hour protected from fire from either side. Is the code calling for 4 layers of drywall all the way around my wires to obtain 2 hour protection or CIC rated wire?

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Most 2 hour rated walls have double drywall on both sides. You wouldn't need 4 sheets on each side. They get their rating by how they are assembled, what the studs are made from, what type and thickness drywall is used, and how penetrations are made. A 2 hour rated wall should survive a 2 hour fire if constructed correctly; the 4 layers of drywall (2 on each side), plus the ceiling, give the wall its rating

CI cabling is not the same as regular cable inside a 2 hour rated assembly.

http://comtrancorp.com/product-section/fire-resistive/

I have had building inspectors not allow any non-related cable to be inside stairwell walls.

 

[bubbarhd]

Welcome to the forum



Most 2 hour rated walls have double drywall on both sides. You wouldn't need 4 sheets on each side. They get their rating by how they are assembled, what the studs are made from, what type and thickness drywall is used, and how penetrations are made. A 2 hour rated wall should survive a 2 hour fire if constructed correctly; the 4 layers of drywall (2 on each side), plus the ceiling, give the wall its rating

CI cabling is not the same as regular cable inside a 2 hour rated assembly.

http://comtrancorp.com/product-section/fire-resistive/

I have had building inspectors not allow any non-related cable to be inside stairwell walls.

Thank you for the reply. In discussions about this the argument people have posed is that 2 hours protection is not achieved when inside the assembly because the 2 hour rating comes from a fire transfer of distruction from one side, outside the 2 layers drywall, completely to outside of the other side of the wall's 2 layers of drywall. If my wire is inside a wall or shaft, it is therefore only 1 hour protected. This is why I am not clear. Do you happen to know of a building code section that defines 2 hour assemblies and how they are constructed.

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