Romex Cover

[nmorgan]

Does anybody know where the requirement for 334.10 (3) comes from, or what the reasoning behind romex needing to be covered in nonresidential uses is? I have heard it is due to the toxic smoke that is produced when romex burns, but I can't find it written anywhere, or any explanation for that matter. NEC commentary only explains the different building types, not the reason for the 15-minute thermal barrier. Any help, or any direction to look in would be greatly appreciated.

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334.10 Uses Permitted​

Type NM and Type NMC cables shall be permitted to be used in the following, except as prohibited in 334.12:

1. One- and two-family dwellings and their attached or detached garages, and their storage buildings.
2. Multi-family dwellings permitted to be of Types III, IV, and V construction.
3. Other structures permitted to be of Types III, IV, and V construction. Cables shall be concealed within walls, floors, or ceilings that provide a thermal barrier of material that has at least a 15-minute finish rating as identified in listings of fire-rated assemblies

Thank you,
Nick

 

[don_resqcapt19]

It was the result of the "horse trading" that went on when the 3 story limitation was removed from the code. Without the "concealment" language, there would not have been enough panel members voting in favor of removing the 3 story limitation. The addition of the restriction on 334.10(3) to the proposal to removed the 3 story limitation got the panel to the required 2/3s majority to accept a code change.

Sure there was lots of discussion of the toxic smoke, but when you think about the small quantity of toxic smoke emitting materials in the electrical system and compare that to the volume of such materials in the building finishes and furnishings, it is not a real world thing.

This was also part of the long standing fight in the code making panels between the cable people and the metal raceway people.

 

[tom baker]

I was at that meeting, long lines of people commenting for and against the proposal. Seems like that ability to comment at the annual meeting was then made much harder.