Associated intrinsically safe apparatus and associated nonincendive field wiring apparatus that are not protected by an alternative type of protection shall not be marked with the class, division, group, or temperature class. Associated intrinsically safe apparatus and associated nonincendive field wiring apparatus shall be marked with the class, division, and group of the apparatus to which it is to be connected.
(d) Simple Apparatus. "Simple apparatus" as defined in Article 504, shall not be required to be marked with class, division, group, temperature class, or ambient temperature range.
(D) Temperature.
(1) Class I Temperature. The temperature marking specified in 500.8(C) shall not exceed the ignition temperature of the specific gas or vapor to be encountered.
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.
(2) Class II Temperature. The temperature marking specified in 500.8(C) shall be less than the ignition tem- perature of the specific dust to be encountered. For organic dusts that may dehydrate or carbonize, the temperature marking shall not exceed the lower of either the ignition temperature or 165°C (329°F).
FPN: See NFPA 499-2004, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemi- cal Process Areas, for minimum ignition temperatures of specific dusts.
The ignition temperature for which equipment was approved prior to this requirement shall be assumed to be as shown in Table 500.8(D)(2).
Table 500.8(D)(2) Class II Temperatures
Equipment (Such as Motors or
Power Transformers)
(American) Standard Pipe Taper (NPT) thread that provides a taper of 1 in 16 ( 3/4-in. taper per foot). Conduit and fittings shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and to ensure the explo-sionproof integrity of the conduit system where applicable. Equipment provided with threaded entries for field wiring connections shall be installed in accordance with
500.8(E)(1) or (E)(2). Threaded entries into
explosionproof equipment shall be made up with at
least five threads fully engaged.
Exception: For listed explosionproof equipment, factory threaded NPT entries shall be made up with at least 4'/2 threads fully engaged.
(1) Equipment Provided with Threaded Entries for NPT Threaded Conduit or Fittings. For equipment provided with threaded entries for NPT threaded conduit or fittings, listed conduit, conduit fittings, or cable fittings shall be used.
FPN: Thread form specifications for NPT threads are lo- cated in ANSI/ASME B 1.20.1-1983, Pipe Threads, Gen- eral Purpose (Inch).
(2) Equipment Provided with Threaded Entries for Metric Threaded Conduit or Fittings. For equipment with metric threaded entries, such entries shall be identified as being metric, or listed adapters to permit connection to conduit or NPT-threaded fittings shall be provided with the equipment. Adapters shall be used for connection to conduit or NPT-threaded fittings. Listed cable fittings that have metric threads shall be permitted to be used.
FPN: Threading specifications for metric threaded entries are located in ISO 965/1-1980, Metric Screw Threads, and ISO 965/3-1980, Metric Screw Threads.