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Mystery Electronics, LLC
6438 Morton Road
Greenbrier, TN 37073
800 798 2256 sales
615 643 8460 voice
615 643 8464 fax
www.mysteryelectronics.com
TechNote TN25
Rev. 1
RE: Installation Instructions for BBTC1 and BBTC2 Backboxes
Important Note:
Mystery Electronics backboxes are UL listed and conform to all applicable N. E.M.A. Standards. While locall y available boxes ma y
seem acceptable as substitutes, there are differences in certain critical dimensions. For a fas t and easy installation and to avoid
costly onsite rework, the user is strongly cautioned to use o nly Myster y Electronics backboxes. The y are proven to be the l owest
cost alternative.
Dimensions:
A B C
BBTC1
BBTC2
Knockout patterns:
Trade size - patterns same on opposite sides.
Two sides: Two sides:
nominal in inches
6 4 4
10½ 4 4
Fig.1
C
Y
X X
1.621.62
X = ½ & ¾” Y = ¾ & 1”
X
1.62
Y
B
A
Notes:
1) Backbox shall be mounted such that cover of box shall be not less than 1/2” or not more than 1” below
finished floor to allow proper depth to mount appropriate TC series floor box.
2) On projects where fork lifts and other heavy equipment are present during construction, cover the backbox
with adequate material (steel plate or equal) affording maximum protection as required.
3) Backboxes installed in floating floors require special consideration – contact factory for details.
Wooden construction -
see Fig.2
As floor box may be subjected to long-term traffic and occasional heavy loads, it is strongly recommend that firm
attachment of the backbox to the framing be made with four (4) each #8 or larger screws fastened on at least two
(2) planes (sides), minimum. Nails will not offer long term installation integrity as they work loose over a very short
time period. Additional blocking or framing may be required to provide solid attachment of the backbox as per
Notes & details herein.
When placement adjacent to structural framing is not possible, blocking must be placed at the sides of the hole
that is cut for the backbox. Blocking of 1” x 2” minimum must be screw attached to the floor decking on each side
of the hole. Blocking should be a few inches longer than the dimension of the hole on the two sides that are
parallel to the hinge of the TC unit. Feed each strip down into the cutout hole and pull it up against the underside
of the floor. Place #8 or larger flat head wood screws on 3” centers thru the floor 1” back from edge of hole along
each side into the blocking. Secure backbox to blocking as above. When TC unit is installed, the floor will be
clamped securely between the TC cover and the blocking strip.
AAA020JA11 p.1/2
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Fig.2: Wood Floor
Floor Decking
1/2"Min. 1"Max. (Note 1)
Backbox
Carpet
Joist
Concrete construction -
see Fig.3
The Mystery Electronics TC Series are not recommended for unprotected outdoor or indoor wet, damp or severe
weather locations. Certain local building codes may require that the backbox be coated with pitch for below
ground applications. This can be done by spraying the outer surface of the box with automotive undercoating
material available in spray cans from most auto parts or discount department stores (Wal-Mart , etc.). It is
additionally advised that the contractor close all open cracks with packaging tape, duct tape, or similar to prevent
concrete slurry from seeping into backbox during the concrete pour.
To automatically adjust for proper backbox depth before concrete is poured; attach a piece of ½” plywood of the
same dimension as the backbox to the top of the box with screws. Screed concrete flush to the top of the
plywood. This will result in the box being at the proper depth of ½” below the finished concrete surface as per
Notes & details herein. Adjust depth accordingly when composite floor structures and materials are built over
concrete.
Fig.3: Concrete Floor
1/2"Min. 1"Max. (Note 1)
Plywood
Backbox
Concrete
AAA020JA11 p.2/2
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