FPN: For information regarding ignition temperatures of gases and vapors, see NFPA 497-2004, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas; and IEC 60079-20-1996, Electrical Apparatus for Explosive
Example: Class I Zone 0 AEx ia IIC T6
Area classification ----------------------- 1
Symbol for equipment built to American------------- ' standards
Type(s) of protection designation----------------------------1
Gas classification group (not required for protection --------------- ' techniques indicated in 505.6, FPN No. 2)
Temperature classification -----------------------------------------------------
FPN Figure 505.9(C)(2) Zone Equipment Marking. Table 505.9(C)(2)(4) Types of Protection Designation
Designation Technique Zone*
d Flameproof enclosure 1 e Increased safety 1 ia Intrinsic safety 0 ib Intrinsic safety 1
[ia] Associated apparatus Unclassified** [ib] Associated apparatus Unclassified** m Encapsulation 1
ma Encapsulation 0 mb Encapsulation 1 nA Nonsparking 2
equipment
nC Sparking equipment in 2 which the contacts are
suitably protected other than by restricted breathing enclosure
nR Restricted breathing 2 enclosure
o Oil immersion 1 px Pressurization 1 py Pressurization 1 pz Pressurization 2 q Powder filled 1
*Does not address use where a combination of techniques is used.
**Associated apparatus is permitted to be installed in a hazaidous
(classified) location if suitably protected using another type of protec-
tion.
Gas Atmospheres, Data for Flammable Gases and Vapours, Relating to the Use of Electrical Apparatus.
(1) Temperature Classifications. Equipment shall be marked to show the operating temperature or temperature class referenced to a 40°C (104°F) ambient. The temperature class, if provided, shall be indicated using the temperature class (T Code) shown in Table
505.9(D)(1).
Electrical equipment designed for use in the ambient temperature range between -20°C and +40°C shall require no additional ambient temperature marking.
Electrical equipment that is designed for use in a range of ambient temperatures other than -20°C to +40°C is considered to be special; and the ambient temperature range shall then be marked on the equipment, including either the
Table 505.9(D)(1) Classification of Maximum Surface
Temperature for Group II Electrical Equipment
Temperature Class Maximum Surface
(T Code) Temperature (°C) Tl <450
T2 <300
T3 <200
T4 <135
T5 <100
T6 <85
symbol 'Ta" or 'Tamb" together with the special range of ambient temperatures, in degrees Celsius.
Electrical equipment suitable for ambient temperatures exceeding 40°C (104°F) shall be marked with both the maximum ambient temperature and the operating temperature or temperature class at that ambient temperature.
FPN: As an example, such a marking might be "-30°C to
+40°C."
Exception No. 1: Equipment of the non-heat-producing type, such as conduit fittings, and equipment of the heat-producing type having a maximum temperature of not more than 100°C (212°F) shall not be required to have a marked operating temperature or temperature class.
Exception No. 2: Equipment identified for Class I, Division 1 or Division 2 locations as permitted by
505.20(B) and
(D) shall be permitted to be marked in accordance with
500.8(C) and Table 500.8(C).