National Electrical Code , flame

To cover the 1987 NEC (National Electric Code) flame and smoke performance guidelines which took effect in the U.S., industry generally uses a non-flame-retardant polyolefin as the insulation material and a highly flame-retardant PVC as the jacketing. If greater flame retardancy is required, fluoropolymers can be incorporated in the system. 

Explosion-proof enclosures are characterized by strong metal enclosures with special close-fitting access covers and breathers that contain an ignition to the inside of the enclosure. Field wiring in the hazardous environment is enclosed in a metal conduit of the mineral-insulated-cable type. All conduit and cable connections or cable terminations are threaded and explosion-proof. Conduit seals are put into the conduit or cable system at locations defined by the National Electric Code (Article 501) to prevent gas and vapor leakage and to prevent flames from passing from one part of the conduit system to the other. 

The concepts of the National Electrical Code (NEC) gronps and the Maxi-mnm Experimental Safe Gap (MESG) are important criteria in the selection and specification of dry type flame arresters. These are explained below. 

Flame arresters are categorized by the MESG of the gas being handled and its corresponding classification by the National Electrical Code (NEC) groups in the US or the International Electrotechnical Commission (lEC) groups in Europe (see Chapter 5). 

Fluoroplastics have been used as wire coatings in military and aerospace applications since their discovery. They have also found their way into wire and cable applications that required extreme performance based on thermal extremes (cryogenic and high temperature applications), chemical resistance, etc., but the major market expansion in fluoroplastic use in the wire and cable industry occurred in North America when the National Electric Code (NEC) allowed polymers with low smoke-generation and flame-spread to be installed in building plenums without metal conduits. 

Section 450-23 of the National Electrical Code specified in the past that the controlling provision for fluids used in indoor transformer applications should be that the insulating liquid have a 300 C fire point. The required temperature has some validity in that it is known that flaming will not persist in a wood slab not subjected to supplemental heating unless the average temperature within the slab is greater than about 320 C. 

Check proximity of flammable materials to any potential ignition sources. Open flames and devices that generate sparks should not be near fiammables. Pay special attention to devices placed in fume hoods that do not meet National Electrical Safety Code (U.S. DOC, 1993) Division 1, Group C and D explosion-resistance specifications for electrical devices. Stirrers, hot plates, Variacs, heat tape, outlet strips, ovens (all types), refrigerators, flame sources (e.g., flame ionization detectors (FIDs) and atomic absorption spectrometers), and heat guns constitute the majority of devices that do not typically conform to these code requirements (see section 8.C.6.1). 

---