Chapter 5 Wiring Methods 61
Copyright Goodheart-Willcox Co., Inc.
Figure 5-6. Cable must be supported vertically within the
maximum support distance. Clamping the conductors to the
junction box is one method of vertical support.
metal conduit and liquidtight flexible metal conduit are
also permitted in short lengths (not more than 4′) to
connect sensors, louvers, and other devices permitted in
these plenums.
For other types of air-handling ducts, refer to Code
Section 300.22(C) and the local inspection authority,
which may have special requirements applicable to the
specific conditions.
Temporary Installations
The provisions of Article 590 of the Code are specif-
ically tailored to apply to temporary electrical wiring
methods, which may be less exacting than a permanent
wiring system. Temporary wiring installations are allowed
for the purpose of providing power and lighting to facili-
ties during construction. Temporary wiring can also be
used for testing, experimental, and developmental
purposes. Upon completion of the activity, the temporary
lighting must be removed.
Bear in mind that Article 590 simply modifies Code
requirements, and that except for those specifically modi-
fied under that article, all other requirements of the Code
apply. Some of the modifications and specific require-
ments for temporary wiring are as follows:
• All lamps for general lighting will be protected from
breakage by a guard over or around the lampholder.
• Splices in conductors do not require junction or
splice boxes if the conductors are part of a multi-
conductor cable or open conductors.
• Ground-fault circuit-interrupters are required for all
125-volt, single-phase, 15- and 20-amp receptacles
that are not fed from permanent wiring circuits.
• Regularly scheduled maintenance checks will be
performed on equipment grounding conductors.
The checks will be performed at not more than
three month intervals and will verify continuity,
any damaged condition, and proper polarity rela-
tive to the grounding electrode conductor.
NEC NOTE 590.3(B)
Temporary electrical power and lighting for holiday
decoration and similar purposes is allowed for a period
not to exceed 90 days.
Wiring Methods
There are three broad classes of wiring methods:
cable, raceways, and cable trays. All of the methods are
used to connect the power supply, devices, and switches
in an electrical circuit.
Cable consists of several conductors wrapped by a
flexible outer covering. Raceways are enclosures installed
between equipment or devices that are to be connected by
conductors. The conductors or cables are placed inside
the raceway, which protects and supports the wiring.
Unlike raceways, cable trays are not enclosed; they are
simply trays on which cables are laid.
Multiconductor Cable
Multiconductor cables are flexible assemblies of
conductors having an overall protective covering. There
are essentially four major types of multiconductor cable
assemblies:
• Service-entrance cable
• Armored cable
• Nonmetallic-sheathed cable
• Metal-clad cable
Service-entrance cable (SE, USE, and ASE)
Service-entrance cable has conductors that can be
used not only for service-entrance wiring, but also for
indoor applications. Type SE, as shown in Figure 5-7, is
unarmored, moisture resistant, and flame retardant. It can
be composed of two or three insulated conductors and an
additional bare conductor. It is readily available in AWG
sizes 12 AWG through 4/0 AWG.