National Electric Code area

Electiical classification. Article 500 of the National Electric-Code provides for the classification of the hazardous nature of the process area in which the measurement device will be installed. If the measurement device is not inherently compatible with this classification, suitable enclosures must be purchased and included in the installation costs. 

In Division 1 areas, the National Electrical Code (NEC) allows only the following wiring methods ... 

Define plant areas requiring explosion-proof, drip-proof and open motor and associated electrical components. Refer to National Electrical Code and National Electrical Manufacturer s Association Standards. 

The design of electrical equipment and instrumentation is based on the nature of the process hazards or specific process classifications. The classification method is defined in the National Electrical Code it is a function of the nature and degree of the process hazards within a particular area. The rating method includes Classes I, II, and III, Groups A-G, and Divisions... 

At all intakes for fresh air or HVAC systems to buildings in an electrically classified area according to the National Electrical Code (NEC) or subject to ingestion of combustible vapors. Especially if they are considered inhabited, critical or of a high value. Typically control rooms, critical electrical switchgear, or main process area power sources are provided with gas detection. 

Other standards in the safety area that are most often citied by OSHA and which must be considered in detailed designs are the. National Electric Code and Machinery and Machinery Guarding. A cursory investigation by a designer of these and other OSHA standards quickly points out several problems, particularly in interpretation. The standards frequently do not allow for alternate... 

The use of electrical equipment in hazardous areas is covered by the National Electrical Code, NEPA 70 (2006), National Fire Protection Association standards NFPA 496 (2003) and NEPA 497 (2004), and OSHA standard 29 CFR 1910.307. The American Petroleum Institute Recommended Practices API RP 500 (2002) and API RP 505 (1997) should also be consulted. 

Articles 500 and 505 of the National Electrical Code (NFPA 70) define classified areas in which flammable materials may be present at high enough concentrations to be ignitable. In a Class I location, the ignitable material is a gas or vapor. Class I locations are further divided into either Divisions or Zones as follows ... 

The control unit can also be isolated from the hazardous area with an appropriate barrier according to code. To understand the appropriate placement of electronic and electrical equipment in hazardous locations, review The NFPA s National Electrical Code, referred to as NFPA 70. Articles 500-516 are particularly relevant. 

When electrically driven equipment is to be operated in an XP and/or an electrically classified area (meaning flammable vapors are, or could be, present), it must be rated to operate in that environment. This means that the ignition source associated with the electricity used to power the equipment must be sealed to prevent the flammable vapors from infiltrating the housing (usually done by the manufacturer). The robustness and the integrity of these seals dictate whether the equipment can be operated in an environment where flammable vapors are always present [National Electric Code (NEC) Class 1 Division 1 area] or where flammable vapors could be present (NEC Class 1 Division 2). 

The National Electrical Code (NEC) classifies hazardous areas of various types and states what sort of equipment is safe for use in each. Refineries and petrochemical plants are most concerned with those areas which the NEC calls Class I. Class I locations are those in which flammable gases or vapors are or may be present in the air in amounts large enough to produce ignitable or explosive mixtures. 

The real world test parameters discussed above have been incorporated into the fire hazard assessment model used by UL (Webber 1983) to determine the compliance of transformer fluids with section 450.23 of the National Electrical Code. In order to be compliant with the code, transformers insulated with less-flammable liquids are permitted to be installed without a vault in Type I and Type II buildings of approved noncombustible materials in areas in which no combustible materials are stored, provided there is a liquid confinement area, the liquid has a fire point of not less than 300 C and the installation complies with all restrictions provided for in the listing of the liquid. UL has identified the need for pressure relief devices and current limiting fusing to limit the effect of possible high current arcing faults. 

Among the ANSI standards is the National Electrical Code (NEC) which is directed at the elimination or control of electrical hazards. It defines the classification of areas according to the degree of hazard possibly foimd in the atmosphere and prescribes wiring methods, grounding, control, etc. These factors are important in motor selection. The NEC is a product of the National Fire Protection Association (NFPA). 

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