locations of boxes ques ?

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wireman1

wireman1

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what article in the nec prohibits boxes from being placed back to back in the same cavity or plane in hotel or motel rooms? is this because the fire rating of the wall would be changed by doing this?is the min. distance 24 ins. between cavitys to mount the other boxon the opposite wall? also i was at a seminar and i though one of the vendors was displaing a box that was ul listed for back to back mounting
 
wireman1 said:
what article in the nec prohibits boxes from being placed back to back in the same cavity or plane in hotel or motel rooms? is this because the fire rating of the wall would be changed by doing this?is the min. distance 24 ins. between cavitys to mount the other boxon the opposite wall? also i was at a seminar and i though one of the vendors was displaing a box that was ul listed for back to back mounting
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Here is what the 06 IBC section 712.3.2 Exception 1 says about the use of metal electrical boxes back to back in a maximum 2 hour rated wall.

1. Membrane penetrations of maximum two-hour
fire-resistance-rated walls and partitions by steel
electrical boxes that do not exceed 16 square
inches (0.0103 m2) in area, provided the aggregate
area of the openings through the membrane does
not exceed 100 square inches (0.0645 m2) in any
100 square feet (9.29m2) of wall area. The annular
space between the wall membrane and the box
shall not exceed 1/8 inch (3.1 mm). Such boxes on
opposite sides of the wall or partition shall be separated
by one of the following:
1.1. By a horizontal distance of not less than 24
inches (610 mm);
1.2. By a horizontal distance of not less than the
depth of the wall cavity where the wall cavity
is filled with cellulose loose-fill,
rockwool or slag mineral wool insulation;
1.3. By solid fireblocking in accordance with
Section 717.2.1;
1.4. By protecting both outlet boxes with listed
putty pads; or
1.5. By other listed materials and methods.
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Exception 2 deals with listed electrical boxes of any material.

2. Membrane penetrations by listed electrical boxes
of any material, provided such boxes have been
tested for use in fire-resistance-rated assemblies
and are installed in accordance with the instructions
included in the listing. The annular space
between the wall membrane and the box shall not
exceed 1/8 inch (3.1 mm) unless listed otherwise.
Such boxes on opposite sides of the wall or
partition shall be separated as follows:
2.1. By a horizontal distance of not less than 24
inches (610 mm);
2.2. By solid fireblocking in accordance with
Section 717.2.1;2.3.
By protecting both boxes with listed putty
pads; or
2.4. By other listed materials and methods.
3. The annular space created by the penetration of a
fire sprinkler, provided it is covered by a metal
escutcheon plate.
Click to expand...

I know that Allied makes some fiberglass boxes that are listed for back to back installation in a 2 hour wall with a separation distance of 6 inches.

Here is a link to Allied and some information on their boxes.

Chris
 
What you need to know about back to back boxes is in the Gypsum Manual.

Some of the fire protection (3M, Hilti) people will allow you to put boxes back to back if you fire pad them, but I would check with your AHJ

The Allied boxes actually allow you to reduce the clearance to 3".

Any mutli family or hotel / motel, is one hour unit to unit walls and floor/ceiling assemblies, unit to corridor and corridor lid, elevator shafts, etc.
 
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