Many rooms require multiple ceiling lights. If only
two lights are involved, measure half the length of the
room and then run diagonals for each half, as shown in
figure 5-21, view C. This measurement procedure gives
you the location for each light. A room that is to be lit
with a row of lights will have them installed along the
center line. The lights should be spaced so that the
lighting is as uniform as possible. You can determine
the spacing by dividing the length of the room by the
number of lights. This figure is the space that is to be
left between any two adjacent lights. The light at each
end of the row is placed at half the preceding distance
from the wall. This spacing is shown in figure 5-21,
view D. If you take another look at view C, you will see
that the space from the end walls to the lights is also half
that of the space between the lights.
Installation of electrical circuits with nonmetallic
cable is fairly simple. It is usually done in two stages.
The two stages are called roughing in and finish work.
Roughing in is the work done before the walls and
ceilings are put in place, and finish work is just what it
implies, the finishing up. You splice wires as needed
and install the receptacle outlets, switches, and lighting
The main objectives in roughing in are to get
circuits routed properly, to reduce the chance of damage
to the cable during installation, and to reduce the chance
of damage while the structure is being finished or during
Figure 5-22.Nonmetallic cable staples.
later modifications. You should refer to Article 300
NEC© for wiring methods.
When roughing in your circuits, study your
electrical blueprints. They will show the general
location of the outlets and switches and how the cable is
to be routed. The exact spot where each outlet and
switch are to be put is determined by the requirements of
the NEC© and the experience of you, the electrician,
unless specific directions are given.
A straight line is the shortest distance between two
points. This principle is used a great deal of the time by
electricians when they are routing cables. Cable is run
from box to box by the shortest route unless there is a
good reason not to do this. Such routing does not always
look neat, but it keeps the cost of material and labor
down, and since most wiring is concealed, it is not often
Cable must be fastened in place to support it and to
prevent strain at boxes and connections. Cable must be
anchored within 12 inches of a box, cabinet, or fitting
and at points no more than 4 1/2 feet apart between
boxes. NM cable is usually attached to wooden framing
studs by staples (fig. 5-22). Care must be taken not to
drive the staples in tight enough to damage the cable.
Another method for securing Romex is by the use of
straps. Figure 5-23 shows four types of straps that may
be used to secure cables.
Concealed cable is installed either through holes
bored in wooden framing studs or into notches cut in
their edges. Holes can be bored with various sixes of
bits, depending upon the size of hole needed. The holes
should be drilled in the center of framing studs in a
straight line and at the least possible angle either
Figure 5-23.Straps for fastening cable.