UFC 3 -520-01
June 10, 2002
Locations that are adjacent to a Class I, Division 1 location and to which ignitable
concentrations of gases or vapors might occasionally be communicated unless such
communication is prevented by adequate positive -pressure ventilation from a source
of clean air, and effective safeguards against ventilation failure are provided.
Evaluate each location for a possible classification as a hazardous area. All
hazardous areas must comply with the design criteria specified in NEC Articles 500 and
501 (2002 Edition) . Refer to NEC Article 504 (2002 Edition) for the design criteria for
intrinsically safe systems.
The Zone classification system described in NEC Article 505 [2002 Edition]
can be applied as an alternative to the Class and Division designations.
Refer to NEC Article 511 (2002 Edition) for design criteria for commercial-type
garages in which service or repair operations are performed on all or all types of self -
Refer to NEC Article 514 (2002 Edition) for design criteria for gasoline
dispensing and service stations. This applies to any location where gasoline or other
volatile flammable liquids or liquefied flammable gases are transferred to the fuel tanks
(or auxiliary fuel tanks) of self -propelled vehicles or approved containers.
Refer to NEC Article 515 (2002 Edition) for design criteria for bulk storage
plants. This applies to any location where flammable liquids are received by tank
vessel, pipeline, tank car, or tank vehicle, and are stored or blended in bulk for the
purpose of subsequent distributing of such liquids.
Wherever possible, do not locate electrical distribution or utilization equipment
in zones classified as hazardous.
400-HERTZ DISTRIBUTION SYSTEMS .
Some equipment is designed for 400-Hertz operation. Normally, a 400-Hertz
voltage is obtained from 60 -Hertz power (50 Hertz outside North America) by motor-
generator sets or UPS conversion equipment. Small 400-Hertz power systems are
often located near the end -use equipment, but larger systems might be installed as
accessory equipment in a nearby electrical equipment room.
A 400-Hertz system requires a different design approach than a 60-Hertz (or
50-Hertz) system. For example, conductors that carry 400-Hertz power cannot be
installed in ferrous metal conduit, but can be installed in aluminum conduit. The high
frequency magnetic fields around conductors carrying 400-Hertz power can induce
heating in ferrous metals, thereby causing excessive temperature rise in the conductors.
Furthermore, greater care is necessary to minimize voltage drop in 400-Hertz systems.