boxes at the proper height, as shown in figure 5-20. Any
number of other guides, such as a rule or a notched stick,
can be used.
It is a fairly common practice to mark the exact
location of each wall-mounted box on the studs
throughout the building before mounting begins. A
lumber crayon, carpenters pencil, or felt-tip pen that
makes an easily seen mark should be used. An
arrowhead, like that shown in figure 5-20, is used to
show where the center of the box is to be placed. The
arrowhead also points to the side of the stud where the
box will be put. As an added convenience, symbols may
be marked near the arrow to indicate the types of device
to be installed. Some examples might be XX for a
duplex outlet, SS for two single-pole switches, S3 for a
three-way switch, or XR for a range outlet.
Switch boxes and outlet boxes for laundry and
utility rooms and garages are normally set 4 feet above
the floor. This height is often increased 4 to 6 inches
when some type of wainscoting or paneling 4 feet high
is to be included as part of the wall. Boxes for outlets
over counter tops are usually installed about 18 inches
above the counter top (see NEC Article 210-52(c)(5)).
This measurement can vary a few inches up or down,
depending on the height of the backsplash panel.
Installing boxes without considering the splash panel
could cause you to have boxes that overlap different
wall surface levels.
Ceiling boxes are located by a completely different
method of measurement. Most rooms have at least one
ceiling light located in the center of the room. A number
of ways can be used to find the spot to mount this light
box. One way is to use a rule or tape to find the halfway
point across one dimension of the room and mark it, as
shown in figure 5-21, view A. Make a second
measurement across the same room dimension and
mark the halfway point. Connect the two marks.
Measure the other room dimension to find the center
and mark it on the preceding line. This point is the place
for the ceiling light box. Figure 5-21, view B, shows
another way to spot the ceiling box. Run diagonals with
string from opposite comers of the room. The point
where the diagonals cross is the room center.
Sometimes the position of the box is laid out on the
subfloor. The point is then transferred to the ceiling by
use of a plumb bob (a pointed weight on a string). When
the plumb bob is suspended by a string held at the level
of the ceiling joists with the point of the weight over the
desired location, the top of the string will be at the spot
where the box is to be mounted.
Figure 5-20.Measuring box mounting height.
Figure 5-21.Location of ceiling lights.