Openings in 2hr fire rated walls

[onetoclarify]

I'm looking for clarfication in the code. All across the country inspectors read this piece of code differently and It would be very helpful if a clarification could be published.

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WALL AND PARTITION ASSEMBLIES

Metallic Electrical Outlet Boxes
Listed single and double gang metallic outlet and switch boxes with metallic or nonmetallic cover 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. (This is the problem sentence)

Metallic boxes located on opposite sides of walls or partitions shall be separated by a minimum horizontal distance of 24in. This minimum separation 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.
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The problem is half of the inspectors believe this refers to the actual surface of the metal box itself and the others believe it relates to the actual opening cut in the fire rated surface that the mud ring protrudes through.

Logic dictates that the problem is the actual opening in the surface of the rated wall. If you had no openings at all in the wall but had a metal box that filled the entire area of the inside of the wall it would not change the fire rating. The intent is to not have a rated wall with a bunch of holes in it. The next sentence refers to "surface" which I believe is the actual meaning. If this is the case shouldn't the sentence read as follows:

The area of the opening cut in a rated wall for individual metallic for outlet or switch boxes shall not exceed 16 sq in. The aggregate openings in the surface area of a rated wall shall not exceed 100 sq in per 100 sq ft of wall surface for any reason.

Please clarify...

 

[cowboyjwc]

Not really that hard to read or understand. The opening in the drywall cannot exceed 16 sq inches, so basically you can't have anything bigger than a two gang box in a one or two hour wall, nor could you have more than twelve single gang or 6 two gang boxes in a 10' x 10' wall space. You also do not have to fire pad metal boxes, except as stated in your post.

Allied does make a listed box that you can use. They now even have a listed 5 gang box.

 

[onetoclarify]

Thanks, this is exactly how I understand the code. Is there anyway to request that the actual sentence in the code be amended or changed to be more clear? We spend so much time fighting with inspectors on this and many times they win and we have to put pads on all the boxes becuase we use 5S boxes in some areas even it there is only two boxes in the 100sq ft area.

 

[bhsrnd]

Thanks, this is exactly how I understand the code. Is there anyway to request that the actual sentence in the code be amended or changed to be more clear? We spend so much time fighting with inspectors on this and many times they win and we have to put pads on all the boxes becuase we use 5S boxes in some areas even it there is only two boxes in the 100sq ft area.

The next revision cycle won't be until around 2010 but start making your list now. Below are links to help you understand the process and download the proposal form. This form may change before the next revision cycle so you may want to download it at that time.

NFPA Code Process

Proposal Form

 

[cowboyjwc]

Yes but this doesn't come out of the NEC, it comes out of the building code. I believe that it is also in either the UL book or the Gypsum Manual.

 

[roger]

Yes but this doesn't come out of the NEC, it comes out of the building code. I believe that it is also in either the UL book or the Gypsum Manual.

I agree, it is not an NEC issue and it is from the UL Fire Resistance Directory

Roger

 

[George Stolz]

I'm all for picking apart a sentence, but I don't get what the other group is thinking. What else would you be measuring besides the size of the hole in the drywall? I'm not seeing the second interpretation, what would they measure?

The burying box analogy isn't helping me either.

 

[kbsparky]

I'm all for picking apart a sentence, but I don't get what the other group is thinking. What else would you be measuring besides the size of the hole in the drywall? I'm not seeing the second interpretation, what would they measure?....

You have stumbled upon one of the main problems in dealing with bureaucracy. Attempting to make mountains out of molehills, to put it in simple terms.