Fire Wall Penetrations

Status
Not open for further replies.
B

bphgravity

Senior Member
Location
Florida
I need some assistance on requirements for cables and conduits penetrating rated walls.

The first question concerns boxes installed in rated walls. I have a contractor that has installed a couple "cut-in" boxes in a 1hr wall for a commercial remodel. According to the section concerning this issue in Volume One of the UL Fire Resistance Directory, "The metallic outlet or switch boxes shall be securely fastened to the studs..."

Based on this, wouldn't this prohibit the use of cut-in boxes? The problem is that there is nothing in both the FBC and the NEC that makes this specification. What enforcement authority do I have referencing a UL spec?

The second issue is concerning the penetrations. The contractor used type MC Cable tested for fire wall penetration. However, the plans did not provide what UL system number the installation is complying with. The contractor used a hammer to bust out a hole approximately 2 in round a passed the cable through at an angle almost parallel to the wall. They then filled the whole with fire caulk. It is my understanding that when penetrating a fire wall with any cable or conduit, it must be at a nearly perpendicular (90?) angle to the wall and the annular space around the opening is limited based on the wiring method type. The contractor is stating that the cable does not pass through the fire wall, but through one side and stays in the wall cavity to a box in the tenant space. They do not feel the penetration must meet a UL system spec.

Any help?
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Bryan, you could use 90.7 to reject the cut in boxes in the fire wall. The Fire Wall is a most likely a UL assembly, so using anything in this wall that specifically has a UL instruction, (ie, the boxes being fastened to the studs) and not following these instructions would not be keeping the wall assembly intact.

As far as the second part, I agree that if the cable does not "through" penetrate, that it needs to be addressed as a single membrane opening, think 16 sq inches.

That said, to get the rating would take both membranes and a void in one would leave the rating less than designed, so IMO I would say look closely at the sealing and let it pass. (notice I did say IMO :))

Roger
 
George Stolz

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
roger said:
That said, to get the rating would take both membranes and a void in one would leave the rating less than designed, so IMO I would say look closely at the sealing and let it pass. (notice I did say IMO :))
Click to expand...

What about a "drywall / void / OSB / void / drywall" setup? Would a hole in one of the layers of drywall change the rating appreciably?
 
Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
The box has a 1 or 2 hour rating. That in itself is not enough. UL Directories will have instructions as to how to properly install a fire rated box in a fire rated assembly wall. Usually the box in itself will not be sufficient, and some kind of putty or other approved (though listing) method will be required (the fire rated assembly also includes the opening around the box - between the box and the wall surface). The manufacturers of fire rated assemblies will gladly help in this assistance, or call UL and the techs there will also assist you.

Once one penetrates one side of a fire rated assembly, that portion has to be repaired to meet the requirements of the UL Fire Rated Assembly. So, yes something is necessary, and I agree with Bryan that a large hole with fire putty or caulk is usually not sufficient.
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Pierre, fireproofing the boxes are not so much a problem here as the mounting. The use of clips or expansion type holders are not allowed in rated walls.

From Volume One of the UL Fire Resistance Directory.



WALL AND PARTITION ASSEMBLIES

Metallic Eletrical Outlet Boxes
Listed single and double gang metallic outlet and switch boxes with metallic or nonmetalliccover plates may be used in bearing and nonbearing wood stud and steel stud walls with ratings not exceeding 2h. These walls shall have gypsum wallboard facings similar to those shown in Design Nos. U301,U411, and U425. The metallic outlet or switch boxes shall be securely fastened to the studs and the opening in the wallboard facing shall be cut so that the clearance between the box and the wallboard does not exceed 1/8 in. The surface area of individual metallic outlet or switch boxes shall not exceed 16 sq in. The aggregate surface area of the boxes shall not exceed 100 sq in per 100 sq ft of wall surface.
Metallic boxes located on opposite sides of walls or partitions shall be seperated by a minimum horizontal distance of 24in. This minimum seperation distance between metallic boxes may be reduced when "Wall Opening Protective Materials" (CLIV) are installed according to the requirements of their Classification. Metallic boxes shall not be installed on opposite side of walls or partitions of staggered stud construction unless "Wall Opening Protective Materials" are installed according to the requirements of their Classification.

George, the problem with your wall is that I can not find a UL assembly to match your design example, so even though it may actually work, untill it is tested and given a design number it won't help.

Notice in the the UL info that 16 square inch openings (4" square box) and up to 100 square inches combined in a 100 square inch area doesn't need any additional treatment.

This is why IMO the cable if sealed properly would not be a problem.

Roger
 
Last edited:
Pierre C Belarge

Pierre C Belarge

Senior Member
Location
Westchester County, New York
Roger

"Pierre, fireproofing the boxes are not so much a problem here as the mounting. The use of clips or expansion type holders are not allowed in rated walls"

I agree with that, I was just adding my 5 cents (used to be 2 cents, but is now 5 cents to adjust for inflation).
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Pierre C Belarge said:
Roger

I agree with that, I was just adding my 5 cents (used to be 2 cents, but is now 5 cents to adjust for inflation).
Click to expand...

And I can truly understand that. :)

Roger
 
sandsnow

sandsnow

Senior Member
Location
Southern California
Membrane penetrations. Our bldg code 1997 UBC tells us to address it as one half of a through penetration. So it must penetrate at a 90 degree angle. There are systems that do allow an angle penetration.

Also it may be a one hour wall, but does it require protected openings. Corridors, Area seperation and occupancy seperation walls are the typical walls that require protected openings. Other one hour walls such as a one hour wall in Type V 1HR, do not require protected openings. Again from our bldg code.
 
scott thompson

scott thompson

Senior Member
Location
Anaheim, California
Same as "Sandstone" (Larry LeVoir), I am in Southern California.

Since the first day I installed an Outlet Box on a Commercial Project, the common consepts of Outlet Boxes installed within rated walls - new or existing, had always been a Box securely fastened to framing members.
(in this case, the most common rated walls dealt with being those of a rated corridor)

Along with this, the Box is wrapped with a "Fire Pad", and the point of penetration for the wiring system to the wall, is sealed with "Fire Caulk"

Back in the 1980's (for me, starting at 1982 and proceeding to 1989), the only thing we would use in rated walls was EMT (as opposed to Aluminum Flex). Some would use Steel Flex, and some guys even went as far as using GRC.
Around 1989, we started using Aluminum Flex - and even MC cable in, and penetrating rated walls.

Even with the various wiring methods, I have never set a Cut-In Box in any rated wall.
If an outlet is added to an existing rated wall, the wallboard is removed between studs, box gets set to a stud, fire pad the box, cut out the original wallboard to fit the ring, replace the wallboard, patch and tape the joints, move on...

Most - if not all of the corridor walls I have dealt with, contain dampening material, so even if one was to attempt to install a Cut-In Box in one of these walls, it would probably be a giant Be-ochh to do so!

Scott
 
Status
Not open for further replies.
Top