Electrical classification

Tayout also has a significant role in minimizing the probability of ignition of a flammable release. Area electrical classification provides the basis for the control of electrical ignition sources. This classification is also used to determine the areas that require protection from vehicular access, etc. Frequently, highly hazardous processes that can result in overpressure (e.g., hydrogenation) are placed behind blast resistant structures/walls. 

Incorrect electrical classification for equipment or auxiliary equipment, lighting, etc., possibly leading to unsafe conditions. 

Base area electrical classification on range of chemicals used... 

Ensure proper design and selection of instrumentation as per area electrical classification... 

Do plant facilities conform to appropriate area electrical classifications ... 

Energy Efficient (EE) Motor Designs, 628 NEMA Design Classifications, 630 Classification According to Size, 630 Hazard Classifications Fire and Explosion, 631 Electrical Classification for Safety in Plant Layout, 647 Motor Enclosures, 649 ... 

Figure 3-8 shows a graphic breakdown of the various electric motors available [8]. The outline in Figure 3-8 is based on an electrical classification. Besides their classification, NEM.A also classified electric motors according to... 

P IDs (3) electrical classification (4) relief system design and design basis (5) ventilation system design (6) design codes and standards (7) material and energy balances for processes built after May 26, 1992 and (8) safety systems. 

Process Facilities 15 Area electrical classification 16 Accessibility for mechanical integrity (sampling, maintenance, repairs) 17 Protection of piping and vessels from vehicles and forklifts 18 Protection of small-bore lines, fittings from external impact, personnel 19 Routing of process piping, critical controls cable trays, critical utilities 20 Vent, drain, and relief valve discharge locations... 

What electrical classification would be specified for an area that has Classes I and II, Groups A and E, and Divisions 1 and 2 motors ... 

Additional information on electrical classification can be found in Chapter 7. 

The classification of electrical equipment should be considered relative to the surrounding equipment and the area electrical classification plan. 

Traditional Electrical Classification System in the United States... 

Table 7-3 provides a comparison between historical and alternative approaches for identifying electrical classification groups. Table 7-4 compares NEC Division and Zone Classification Systems. 

Where ventilation is installed to effect a reduction in the area electrical classification, the rate should be no less than 12 air changes per hour for an adequately ventilated area in accordance with API RP 500. Areas containing ignition sources, such as control and switchgear buildings, gas turbine acoustical enclosures, and power generators, should be pressurized in accordance with NFPA 496, if located in an electrically classified area. 

Enclosures, even partial enclosures, containing equipment handling flammable, combustible, ortoxic materials may permit the accumulation of hazardous concentrations of these materials within the enclosure, potentially resulting in fire, explosion, or personnel exposure. Where the possibility of a flammable spill or release within an enclosure exists, the enclosure design should include a relevant selection from the following features noncombustible construction, adequate ventilation, drainage, appropriate electrical classification, flammable vapor detection, isolation and alarm, and internal automatic sprinkler or water spray protection. 

Where there is exposure from surrounding flammable or combustible process equipment, external fire protection of the enclosure may be needed, based on the importance or value of the protected equipment or instruments. In addition, the interior of the enclosure may require electrical classification, unless the enclosure is purged or pressurized as described in NFPA 496. 

Section 8 outlines the following criteria for selection of measurement devices measurement span, performance, reliability, materials of construction, prior use, potential for releasing process materials to the environment, electrical classification, physical access, invasive or noninvasive, and life-cycle cost. 

Electrical 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. 

The detectors and their wiring must meet the requirement of the area electrical classification in which they are being installed. 

Hazardous features to be considered will include pressure relief handling of hazardous materials such as acids and alkalis protection from steam and other high-temperature fluids and electrical classification for handling solvents or protection from water ingress, high speed rotating machinery, and noise levels. 

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