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Article 505 requires equipment construction and installation that ensures safe performance under conditions of proper use and maintenance.
Informational Note No. 1: It is important that inspection authorities and users exercise more than ordinary care with regard to the installation and maintenance of electrical equipment in hazardous (classified) locations.
Informational Note No. 2: Low ambient conditions require special consideration. Electrical equipment depending on the protection techniques described by 505.8(A) may not be suitable for use at temperatures lower than -20°C (-4°F) unless they are identified for use at lower temperatures. However, at low ambient temperatures, flammable concentrations of vapors may not exist in a location classified Zones 0, 1, or 2 at normal ambient temperature.
(A) Implementation of Zone Classification System
Classification of areas, engineering and design, selection of equipment and wiring methods, installation, and inspection shall be performed by qualified persons.
(B) Dual Classification
In instances of areas within the same facility classified separately, Zone 2 locations shall be permitted to abut, but not overlap, Class I, Division 2 locations. Zone 0 or Zone 1 locations shall not abut Class I, Division 1 or Division 2 locations.
(C) Reclassification Permitted
A Class I, Division 1 or Division 2 location shall be permitted to be reclassified as a Zone 0, Zone 1, or Zone 2 location, provided all of the space that is classified because of a single flammable gas or vapor source is reclassified under the requirements of this article.
(D) Solid Obstacles
Flameproof equipment with flanged joints shall not be installed such that the flange openings are closer than the distances shown in Table 505.7(D) to any solid obstacle that is not a part of the equipment (such as steelworks, walls, weather guards, mounting brackets, pipes, or other electrical equipment) unless the equipment is listed for a smaller distance of separation.
Table 505.7(D) Minimum Distance of Obstructions from Flameproof "d" Flange Openings
Gas Group Minimum Distance
mm in.
IIC 40 137/64
IIB 30 13/16
IIA 10 25/64
(E) Simultaneous Presence of Flammable Gases and Combustible Dusts or Fibers/Flyings
Where flammable gases, combustible dusts, or fibers/flyings are or may be present at the same time, the simultaneous presence shall be considered during the selection and installation of the electrical equipment and the wiring methods, including the determination of the safe operating temperature of the electrical equipment.
(F) Available Fault Current for Type of Protection "e"
Unless listed and marked for connection to circuits with higher available fault current, the available fault current for electrical equipment using type of protection "e" for the field wiring connections in Zone 1 locations shall be limited to 10,000 rms symmetrical amperes to reduce the likelihood of ignition of a flammable atmosphere by an arc during a short-circuit event.
Informational Note: Limitation of the available fault current to this level may require the application of current-limiting fuses or current-limiting circuit breakers.

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505.7 Special Occupancies, Special Precaution
and maintenance of electrical equipment in hazardous (classified) locations. Informational Note No. 2: Low ambient conditions require special consideration ...
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(C) Special Occupancies, Reclassification Permitted
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