UFC 3 -520-01
June 10, 2002
Underfloor ducts can be used in large administrative areas or other areas
where extensive power and communications facilities are required that cannot be
adequately served by normally provided wall outlets. Duct specifications and spacing
should be selected to meet the specific needs of the project.
Busways or cablebus should be used for feeders and service entrances if
dictated by space limitations or if it is determined to be more economical than
equivalent-a mpacity insulated conductors in raceways. Plug -in busways can be used in
industrial or shop areas to serve a variety of power outlets or motors.
Cable trays should be used as a support system for conductor types that
could be otherwise supported, i ncluding metal-clad cable, conductors in conduit,
multiconductor type cables such as underground feeder ( UF) or service entrance (SE),
or single conductors where permitted by the NEC and OSHA 29 CFR 1910.305. Do not
support conduit or cable from or attached to the underside of cable tray.
Cellular steel floor should be used in large structures having extensive power,
lighting, and communications wiring requirements if the combination of structural
adequacy and raceway access capability will result i n major economies compared to
conventional building systems. If the use of cellular steel floor is anticipated, electrical
and structural designs should be closely coordinated, beginning at the earliest
opportunity in the design phase.
Branch circ uit wiring within lightweight, removable, metal-stud partitions
should either be installed in conduit or can consist of properly supported metal-clad
cable or nonmetallic-sheathed cable systems installed through nonmetallic bushed or
grommeted holes or slo ts in the framing members. Outlet boxes for such applications
should be of metal, grounded by the cable -grounding conductors, and securely
supported by bar hang ers or equivalent means within framing members.
Mineral-insulated cable systems, type MI, can be used instead of exposed
conduit and wiring, if required by the application or if it can be shown that it is
economically justified. Mineral-insulated cable will usually not be cost-effective for use.
If used, make cable connections and terminations in accordance with the
manufacturer's recommendations to assure a proper connection.
Surface mounted outlet boxes in conduit and tubing systems in normally dry
locations should be of the cast metal, hub -type or one piece sheet metal with covers
designed for surface work. Do not allow surface boxes with nail holes or openings that
can admit insects.
Protect conductors entering boxes, cabinets, or fittings from abrasion. Close
openings through which conductors enter. Close unused openi ngs in cabinets, boxes,