Class I equipment

Equipment shall be approved not only for the class of location but also for the explosive, combustible, or ignitable properties of the specific gas, vapor, dust, fiber, or flyings that will be present. In addition. Class I equipment shall not have any exposed surface that operates at a temperature in excess of the ignition temperature of the specific gas or vapor. Class II equipment shall not have an external temperature higher than that specified in Section 500-3(1). Class III equipment shall not exceed the maximum surface temperatures specified in Section 503-1. 

Class I Equipment and Systems systems representing processes, equipment, and areas with the highest degree of product quality and regulatory impact. For example ... 

Class I equipment utilizes earth ground and are typically mains operated (i.e., 115/230/400 Vac, 3-5 wires) electrical products such as desktop computers, test and measurement devices, machines, or stationary appliances. 

Combined inspection and testing is also necessary on some equipment because some faults cannot be seen by just looking - for example, the continuity and effectiveness of earth paths on class I equipment. For some portable appliances the earth is essential to the safe use of the equipment and, therefore, all earthed equipment and most extension leads should be periodically tested and inspected for these faults. All portable appliance test instruments (PAT Testers) will carry out two important tests earth bonding and insulation resistance. 

It is important to ensure that all portable electrical equipment is regularly inspected and adequately maintained to minimise the risk of danger to the user. Equipment of the double-insulated or all-insulated types (class II), to the relevant BS , has no provision for earthing and is not earthed. Such equipment should be marked with the s5anbol [ ]. There is no symbol for class I equipment. 

In the case of portable equipment, testing is often carried out using a proprietary portable appliance tester (PAT). One useful test is the measurement of e insulation resistance to confirm that it is sufficiently high to prevent undue current leakage. Additionally, for class I equipment (that must be earthed) it is important to verify that the connection to earth is sound, i.e. its electrical resistance is low, and that the conductor is capable of carrying the sort of high current that may occur under fault conditions. Both the HSE and the lEE have produced guidance on electrical equipment maintenance. ... 

If Class II distribution apparatus or accessories are used. Regulation 471-09-02 requires the protective conductor to be available at each wiring point to allow for the replacement of the Class II by Class I equipment. It is preferable for the apparatus and accessories to be of the all-insulated rather than the double-insulated type to avoid the possibility of exposed conductive parts making fortuitous contact with earthed metalwork. 

There is only limited use of Class II equipment in the fixed installation because in most cases it has to include the protective conductor for use elsewhere in the circuit to connect Class I equipment and this usage negates the Class II classification. Class II is more prevalent in portable apparatus. Protection by non-conducting location is not much used in the UK except for special locations such as test facilities. Earth-free local bonding, again, is used only in special locations where the necessary precautions can be taken to avoid importing an earth. Electrical separation s main application is also in electrical testing areas. 

To avoid the risk of eleetrostatic ignitions. Class II apparatus should not be used and Class I equipment metalwork should be eflfeetively earthed. Light metals and their alloys should be avoided where there is a risk of frictional sparking. 

Class I The Class I BSC provides personnel and environmental protection, but no product protection. It is similar in air movement to a chemical fume cupboard, but has a HEPA filter (see Chapter 9) in the exhaust system to protect the environment (Fig. 10.94). In the Class 1 BSC, unfiltered room air is drawn across the work surface. Personnel protection is provided by this inward air velocity as long as a minimum velocity of 0.37 m s" is maintained through the front opening (see the discussion on fume cupboards in Section 10.2.3.3). In many cases Class I BSCs are used specifically to enclose equipment. 

Some Class I BSCs are equipped with an integral exhaust blower the cab inet blower must be tiiterloclced with the building exhaust fan. In the event that the building exhaust fan fails, the cabinet exhaust blower must also turn off so that the exhaust ducts are not pressurized. If the ducts are pressurized and the HEPA filter develops a leak, contaminated air could be discharged into other parts of the building or the environment. 

The design of intrinsically safe equipment is governed by the rules of NFPA Publication No. 493, Standard for Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous Locations. It is cautioned, however, that the design of intrinsical-... 

In Division 1 areas, meters, instruments, relays, and similar equipment containing high-temperature or arcing devices must be installed in approved explosion-proof or purged enclosures. Unless such devices are specifically labeled as suitable for Class I, Division 1 areas, it is best to assume they are not suitable. 

Electrical Equipment for Use in Class I, Division 2 Hazardous (Classified) Locations... 

Standard for Purged and Pressurized Enclosures for Electrical Equipment in Hazardous (Classified) Locations Recommended Practice for Classification of Class I Hazardous Locations for Electrical Installations in Chemical Plants... 

More recently, the NFPA has used the MESG and the MIC ratio for classifying explosion-proof electrical equipment (NFPA 497 1997), and this approach can also be used for classilying flame arresters. In this method, NEC Class I combustible materials (vapors or gases) are divided into four groups ... 

The schedule sheet which summarizes the key reference data for a particular class of equipment such as pumps, but contains no process data. The latter type is prepared for job coordination with and in the various departments, i.e., engineering, construction, purchasing, production. It primarily serves for the construction period but, of course, does have lasting cross-reference value. 

Type and specifications on fan driver, gear types, pow er voltage, phase, cycles. Motors should at least meet specifications equivalent to totally enclosed, fan cooled, or if in explosive hazardous area, TEFC Class I, Group D (except this not acceptable in hydrogen or acetylene atmosphere). Due to moisture conditions around this equipment, it should be protected against moisture penetration and corrosion. 

Explosionproof Apparatus. The protection technique shall be permitted for equipment in those Class I, Division 1 and 2 locations for which it is approved. 

FPN) Nonincendive circuit is defined in Article 100. For further information, see Electrical Equipment for Use in Class I, Division 2 Hazardous (Classified) Locations, ANSI/ISA-S12.12-1984. 

FPN No. 2) Low ambient conditions require special consideration. Explosionproof or dust-ignitionproof equipment may not be suitable for use at temperatures lower than -25°C (-13°F) unless they are approved for low-temperature service. However, at low ambient temperatures, flammable concentrations of vapors may not exist in a location classified Class I, Division 1 at normal ambient temperatures. 

Exception No. 2 Equipment intended specifically for Class I, Zone 0, Zone 1, or Zone 2 locations shall be grouped in accordance with Section 5 05-5. 

FPN No. 1) For additional information on the properties and group classification of Class I materials, see Manual for Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous (Classified) Locations, NFPA 497M-1991, and Guide to Eire Hazard Properties ofElammable Liquids, Gases, and Volatile Solids, NFPA 325—1994. 

FPN No. 2) The explosion characteristics of air mixtures of gases or vapors vary with the specific material involved. For Class I locations. Groups A, B, C, and D, the classification involves determinations of maximum explosion pressure and maximum safe clearance between parts of a clamped joint in an enclosure. It is necessary, therefore, that equipment be approved not only for class but also for the specific group of the gas or vapor that will be present. 

Exception Equipment installed in a Class I, Division 1 location shall be suitable for the Division 1 location. 

Equipment that is approved for Class I and Class II shall be marked with the maximum safe operating temperature, as determined by simultaneous exposure to the combinations of Class I and Class II conditions. 

Exception No. 3 Eixed general-purpose equipment in Class I locations, other than fixed lighting fixtures, that is acceptable for use in Class I, Division 2 locations shall not be required to be marked with the class, group, division, or operating temperature. 

FPN No. 4) It is necessary that the meaning of the different equipment markings and Group II classifications be carefully observed to avoid confusion with Class I, Divisions 1 and 2, Groups A, B, C, and D. 

Wiring and Eqitipment within Class I Locations. All electric wiring and equipment within the Class I locations defined in Section 515-2 shall comply with the applicable provision of Article 501. 

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