Chapter 5 Wiring Methods 67
Copyright Goodheart-Willcox Co., Inc.
Figure 5-16. ENT is easy to install and can be used in a wide
variety of applications.
as for standard flexible metal conduit. As with standard
metal flex, lengths of 3′ and less need not be supported.
Uses of liquidtight flexible metal conduit include
direct burial, concrete embedment, exposed surfaces, and
through walls (concealed). Sizes of 3/8″ to 1 1/4″ liquidtight
flexible metal conduit are suitable for equipment grounding
in lengths not exceeding 6′; longer lengths and sizes 2″ or
larger require a separate equipment grounding conductor to
be run inside the conduit.
Liquidtight flexible nonmetallic conduit (LFNC)
shares all the same rules as its metallic counterpart except
for the following:
• The maximum permitted size is 2″.
• Lengths of more than 6′ are prohibited.
• The equipment grounding conductor, where
required, is run inside or outside the flex.
Rigid polyvinyl chloride conduit (PVC)
There are several types of rigid nonmetallic conduit
on the market today, but rigid polyvinyl chloride conduit
(PVC) is the most popular. The combination of low cost,
ease of installation, strength, and availability makes PVC
a good choice when a metallic conduit is not required.
Article 352 of the Code addresses the rules regarding
the installation of PVC. You will find in this article that
PVC is permitted to be used in wet locations. This feature
makes PVC an excellent choice for underground, farm,
and outdoor installations. Make sure to use the stronger
schedule 80 PVC for exposed areas of physical damage.
Some of the other considerations when deciding to use
PVC are the following:
• PVC conduit can be used in concealed areas such
as walls, floors, and ceilings.
• Do not use PVC conduit to support any fixtures
or luminaires.
• Do not use PVC conduit in areas with an ambient
temperature in excess of 122° F.
• Use expansion fittings when the length of the conduit
may expand or contract by 1/4″ or more. This can be
determined by using Table 352.44 of the NEC.
• Use bushings when connecting PVC conduit to a
box unless the box, fitting, or enclosure design
provides similar protection.
Electrical nonmetallic tubing (ENT)
ENT is a very versatile wiring method. The tubing is
composed of a corrugated nonmetallic material (typically
plastic). The tubing can be bent by hand, making it very easy
to install, Figure 5-16. ENT is available in 1/2″ to 2″ sizes.
Support for ENT must be provided within 3′ of each
box and every 3′ along the length of tubing. Compared to
other wiring methods, ENT requires more support due to
its flexibility.
Article 362—Electrical Nonmetallic Tubing specifies
the uses for ENT. The following is a partial list of these uses:
• For exposed work in areas not subject to physical
damage in buildings three stories and less.
• Concealed in walls, floors, and ceilings.
• Above suspended ceilings with a 15-minute
finish rating.
• Embedded in concrete.
CAUTION
Some types of ENT may become brittle in cold
temperatures. If the tubing becomes brittle, it could
be easily damaged.
Surface raceway
In many situations there arises a need to add new
circuits in an area where the existing wiring is not acces-
sible. The wiring could be embedded in concrete or in
conduit behind walls.
In such conditions, the needed changes can be made
using surface raceway, Figure 5-17. Surface raceway consists
of one- or two-piece channels and are easily installed. These
raceways are used not only for power outlets and lighting, but
are also permitted, when provided with internal barriers, to
route communication wiring and fire protection cable.
The number of conductors permitted in surface
raceway is not defined by the Code but is provided by the
manufacturer. As with wireway and auxiliary gutters,
splices and taps are permitted (in those raceways having
removable covers) so long as they do not occupy more
than 75% of the cross-sectional area. The one-piece unit
must be installed and secured prior to pulling conductors.
There are numerous types of fittings, switches, recepta-
cles, elbows, and adapters available for surface raceway.