be placed parallel at a turn in a multiple run, as shown
in figure 5-3. If standard elbows are used, it is
impossible to place them parallel at the turns. They will
have an appearance similar to the one shown in figure
Except as discussed in the NEC®, metal raceways,
cable armor, and other metal enclosures for conductors
will be joined together into a continuous electric
conductor and will be connected to all the boxes,
fittings, and cabinets to provide effective electrical
continuity. Raceways and cable assemblies will be
mechanically secured to boxes, fittings, cabinets, and
other enclosures. This action ensures electrical
continuity of metal raceways and enclosures.
WIRING OF BUILDINGS
Normally the power-distribution feeder from the
power pole to a building is secured to the building with
an insulator bracket. Brackets should be mounted high
enough so the power feeders are never suspended
lower than 18 feet over driveways and 10 feet over
Insulator bracket service-entrance conductors run
down the side of the building to a point where they
enter the building and connect to the service-entrance
panel. For commercial and industrial wiring, the
greatest percentage of wiring will be installed in a
Figure 5-3.Right-angle turns with bent conduit.
conduit or a raceway. Service-entrance cable should be
used for this purpose.
Armored cable or nonmetallic-sheathed cable
should be used for the interior wiring of the building.
At each building, the wiring system must be
grounded. This provision is in addition to the ground at
the power pole. Grounds must be established at each
point of entrance to each building; and, if possible, all
these grounds should be tied together on driven
grounds. Also, for added safety, the water system
should be tied at each building to the driven ground for
that building. A well-grounded wiring system adds to
the safety of the entire installation.
WIRING SYSTEM GENERAL
The following discussion applies to the types of
wiring used for voltages up to 600 volts, unless
otherwise indicated. Each type of insulated conductor
is approved for certain uses and has a maximum
operating temperature. If this temperature is exceeded,
the insulation is subject to deterioration. In recent
years, modified ethylene tetrafluoroethylene (2 and
ZW) and perfluoroalkoxy (PFA and PFAH) cables
have been allowed for high-temperature operations.
Each conductor size has a maximum current-carrying
capacity, depending on the type of insulation and
conditions of use.
Conductors of more than 600 volts should not
occupy the same enclosure as conductors carrying less
than 600 volts, but conductors of different light and
power systems of less than 600 volts may be grouped
together in one enclosure if all are insulated for the
maximum voltage encountered. Communication
circuits should not occupy the same enclosure with
light and power wiring.
Boxes or fittings must be installed at all outlets, at
switch or junction points of raceway or cable systems,
and at each outlet and switch point of concealed knob-
PROVISIONS APPLYING TO ALL
The number of conductors, permitted in each size
and type of raceway, is definitely limited to provide
ready installation and withdrawal. For conduit and
electrical metallic tubing, refer to the NEC®.