Raceways, except surface-metal molding, must be
installed as complete empty systems, the conductors
being drawn in later. Conductors must be continuous
from outlet to outlet without splice. except in auxiliary
gutters and wireways.
Conductors of No. 8 AWG and larger must be
stranded. Raceways must be continuous from outlet to
outlet and from fitting to fitting and will be securely
fastened in place.
All conductors of a circuit operating on alternating
current, if in a metallic raceway, should be run in one
enclosure to avoid inductive overheating. If, owing to
capacity, not all conductors can be installed in one
enclosure, each raceway used should contain a
complete circuit (one conductor from each phase).
Rigid-metal conduit, intermediate metal conduit,
and electrical metallic tubing are the systems generally
used where wires are to be installed in raceways. Both
conduit and tubing may be buried in concrete fills or
may be installed exposed. Wiring installed in conduit
is approved for all classes of buildings and for voltages
both above and below 600 volts. Certain restrictions
are placed on the use of tubing; refer to the NEC®.
LIGHTING AND POWER SYSTEMS
Lighting and power systems start at the
panelboards. Refer to the NEC® during the installation
of the lighting and power circuits for further guidance.
The wiring layout in each of these illustrations
determines how the component parts in the circuit will
be connected to one another and where the wires will
be routed. Careful planning in the wiring layout can
result in substantial savings by eliminating long runs of
excess wire. It should be pointed out that the wire runs
that are shown in the actual construction illustration
may not be the most economical use of wire. These
wire runs are laid out in a very smooth and definite
pattern to make the drawing easier to follow. In many
cases, wire runs shown at right angles should be run
diagonally to conserve wire. When cable runs are
routed on the jobsite, shortening the runs will result in
lower installation costs.
SERVICES AND FEEDERS
No limit is placed on the electrical capacity of
service conductors and service protection used in
bringing the electric supply into a building, since only
one supply should be introduced whenever possible.
Near the point of entrance of the supply, the heavy-
service conductors are tapped by feeders that conduct
the electricity to panelboards at various load centers in
the building where the final branch circuits which
supply individual lighting, heating, and power outlets
originate. No limits are placed on the electrical
capacity of feeders; but, for practical purposes, they
are limited in size by the difficulty of handling large
conductors and raceways in restricted building spaces,
by voltage drop, and by economic considerations.
Each lighting fixture, motor, heating device. or
other item of equipment must be supplied by either a
branch circuit for grouped loads, by an individual
branch circuit, or by a motor branch circuit.
LIGHTING AND APPLIANCE BRANCH-
In solving all installation problems with
panelboards, the first consideration is to determine
whether the panelboard will be considered a lighting
and appliance branch-circuit type. The NEC® rules are
much stricter for lighting and appliance branch-circuit
panelboards than for other types.
The Code defines a lighting and appliance branch-
circuit panelboard as one having more than 10 percent
of its overcurrent devices rated 30 amperes or less for
which neutral connections are provided. For example,
if any panelboard with less than 10 overcurrent devices
contains one overcurrent device rated at 30 amperes
for which neutral connections are provided, it would be
considered a lighting and appliance branch-circuit
panelboard (1 9 = 11%).
In another example, panelboards that supply loads
without any neutral connections are not considered
lighting and appliance branch-circuit types whether or
not the overcurrent devices are 30 amperes or less.
When it is determined that a panelboard is a
lighting and appliance branch-circuit type, the
following NEC® rules apply:
1. Individual protection, consisting of not more
than two main circuit breakers or sets of fuses having a
combined rating not greater than that of the panelboard,
is required on the supply side. This main protection may
be contained within the panelboard or in a separate
enclosure ahead of it. Two exceptions to the Code rule
are as follows:
a. Individual protection is not required when
the panelboard feeder has overcurrent protection not
greater than that of the panelboard. For example, two
400-ampere panelboards can be connected to the same
feeder if the feeder overcurrent device is rated or set at
400 amperes or less.