UFC 3 -520-01
June 10, 2002
POWER DISTRIBUTION AND UTILIZATION --RACEWAY AND WIRING
Design raceways used for interior wiring syste ms to comply with the NEC.
Depending on the application, the following raceway types are preferred (other conduit
types can be used for specific applications as justified by the design) :
Rigid, threaded zinc -coated steel conduit typically 40 gauge .
Intermediate metal conduit wall thickness less than rigid conduit by larger than
EMT, typically 20 gauge.
Electrical metallic tubing typically 10 gauge.
Flexible metal conduit.
Surface metal raceways.
Do not use rigid alum inum conduit unless justified by the application and
documented in the design package. For example, aluminum conduit is preferred for
400 Hertz applications. Do not imbed aluminum conduit in concrete or masonry, buried
in earth, or used to penetrate vertical or horizontal firewalls. If conduit runs penetrate
firewalls, use steel conduit for a minimum of 0.9 meters (3 feet) on each side. Do not
mix metal types if avoidable.
Nonmetallic conduit, including flexible nonmetallic conduit, can be used within
structures below concrete slab -on-grade construction and in highly corrosive,
nonhazardous locations where metallic conduits might corrode due to atmospheric
conditions. Nonmetallic conduit is not preferred for general-purpose applications.
Follow NEC criteria for the application of nonmetallic conduit.
Flexible metal conduit is not intended as a general-purpose raceway for long
distances. Use liquid-tight flexible metal conduit for permanent connections to large
appliances, equipment, and motors to allow for vibration or movement. Flexible metal
conduit can be used for lighting fixture connections above suspended ceilings in
accordance with the NEC and with Underwriters Laboratory (UL) listed and labeled
equipment and control assemblies.
Use surface metal raceways or multi -outlet assemblies only for building
improvements or renovations, or for applications where a variety of cord-and-plug
connected equipment will be utilized in a limited space, such as in some areas of
medical facilities, shops, and laboratories.