Willie Pete
Member
Does anyone know how I can protect a Steel City 4 x4 box (which is good for up to two hours) in a 3-Hour rated wall?
Metallic Box In A 3-Hour Wall
- Thread starter Willie Pete
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Can you prefab a sheetrock box around the 4" square box?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Well that's a lot nicer and easier than a sheetrock box. :smile:
- Location
- Logan, Utah
I don't see where the putty pads give a steel box a 3 hour rating. The installation instructions from 3M only show the putty pads on a steel box for a 1 or 2 hour rated wall.
You would have to have a listed membrane penetration assembly that is listed for 3 hours to work in this wall.
Chris
You would have to have a listed membrane penetration assembly that is listed for 3 hours to work in this wall.
Chris
mcclary's electrical
Senior Member
- Location
- VA
I've seen 2 hour putty,,,,but not three hour putty
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If the op already has a 2 hour rating on the walls wouldn't the putty add the extra hour needed?
- Location
- Logan, Utah
Not unless there is a tested assembly using the putty pad to acheive a 3 hour rating.
The problem is that with fire rating you can't just take 2- 1 hour rated pieces of equipment and add them together and get a 2 hour rating. Each rating must be done with a tested assembly.
A standard 4 square metal box without a putty pad is premitted to be used in up to a 2 hour rated assembly provided that they meet the requirements of Exception #1 to 712.3.2 of the IBC.
Chris
Willie Pete
Member
Electrical box in 3-hour wall
Electrical box in 3-hour wall
Bottom line is do any of you think it can be done?
Electrical box in 3-hour wall
Bottom line is do any of you think it can be done?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
Thanks Chris-- so what is the solution-- Sounds like it can't be done but I can't accept that.
Unless you can find a tested assembly listed for use in a 3-hour wall (and I'm not aware of one), the solution would be surface mount. If the owner doesn't want to see surface mounted boxes, the wall could be furred out so that the box is flush mounted, but the real 3-hour wall membrane is behind it.
Flex
Senior Member
- Location
- poestenkill ny
2 pieces of sheetrock double the fire rating
- Location
- Logan, Utah
Not necessarily, for example Table 721.2.1.4(2) assigns a time rating of 40 minutes to a single layer of 5/8 Type X gypsum board, but most people would say a wall built with a single layer of 5/8" Type X would be 1 hour. That is because there are many tested fire rated assemblies that use a single layer of 5/8" type X in conjunction with the material of the wall and during test the entire wall had a performance of a 1 hour wall.
What you have to understand is that a fire resistance rated wall needs to be built using a tested assembly. For example the Gypsum Association produces a fire resistance design manual that has many different types of walls that can be built and have different ratings.
Chris
Flex
Senior Member
- Location
- poestenkill ny
I see, and I am assuming the Fire Putty Pad company doesnt goto that extent. That why its only good for an hour?
- Location
- Logan, Utah
3M has tested their putty pads for up to a 2 hour rated wall. My guess is that the putty pads failed on a 3 hour test or 3M never had the pads tested for a 3 hour wall.
Chris
Flex
Senior Member
- Location
- poestenkill ny
Thanks I appreciate the info
- Location
- Logan, Utah
- Status