Chapter 5 Wiring Methods 69
Copyright Goodheart-Willcox Co., Inc.
Additional information and requirements concerning
the design and use of wireways can be found under
Article 376 and Article 378 of the Code. Some key points
within this article include the following:
• Wireways are not to be installed where subject to
damage.
• Wireways are not to be placed in corrosive
environments.
• Wireways are not to be concealed.
• Wireways are normally restricted to no more
than thirty current-carrying conductors. More
than thirty current-carrying conductors can be
contained in a wireway if their ampacity rating is
derated per Section 310.15(B)(3)(a) of the Code.
NEC NOTE 376.22(B), 378.22
Conductors for signaling circuits or controller
conductors between a motor and its starter and used
only for starting duty shall not be considered as
current-carrying conductors.
Auxiliary gutters
Essentially identical in construction and appearance
to wireways, auxiliary gutters are primarily used to
extend or supplement wiring spaces at load centers,
transformers, and metering cabinets. Auxiliary gutters
cannot extend beyond 30′ from the equipment they
supplement. The same rules regarding fill (20%) and
splices or taps (75%) apply as with wireways.
Busways
Busways are sheet metal enclosures into which
conductors are installed at the factory. These conductors,
which are actually copper or aluminum busbars, are
supported by insulating material. Busways commonly
come in up to 10′ sections that are bolted together. When
installed horizontally, busways require supports every 5′
unless otherwise designated. Busway systems are often
used in commercial buildings as the primary wiring
method.
There are three types of busways available:
• Feeder busways
• Plug-in busways
• Trolley busways
A plug-in busway is illustrated in Figure 5-19.
Although the initial cost of busway material is higher
than other wiring methods, the installation labor costs are
much lower. This often makes it a more cost-effective
system.
There are numerous wiring methods that are permitted
for use with busways as taps or branch circuits:
• Rigid nonmetallic conduit (PVC)
• Electrical nonmetallic tubing (ENT)
• Intermediate metal conduit (IMC)
• Electrical metallic tubing (EMT)
• Flexible metal conduit
• Rigid metal conduit
• Armored cable (AC)
• Surface metal raceway
Figure 5-18. This table lists allowable fill for common wireway
sizes.
Wireway Size Cross-Sectional Area
(in2)
(in.)
100% 75% 20%
2 1/2 × 2 1/2 6.25 4.68 1.25
4 × 4 16 12 3.20
6 × 6 36 27 7.20
8 × 8 64 48 12.80
Wireway Cross-Sectional Area
Figure 5-19. Plug-in busways provide many locations for an
electrical hookup. (Star Products Division, US Trolley Corp.)