01 June 2003
Hazardous location categories: zones vs. divisions
Wiring practices in hazardous locations are still subject to debate—whether the U.S. should change its method of classifying locations by divisions and adopt the European method of zone classification. It's also affecting businesses throughout the industry. Some fear the zone method would replace existing jobs because of the lack of conduit installations in zone-classified equipment. Others say it's economically smart to switch; the installation materials are less expensive. Here's an easy way to see the differences between the zones and divisions, as portrayed by UL's Hazardous Locations Services.
Class I
Flammable gases, vapors, or liquids
Class I area classification
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Class 1 groups
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Class I temperature codes
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Class II
Combustible dusts
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Class II area classification Division 1: Where ignitable concentrations of combustible dusts can exist all the time or some of the time under normal operating conditions. Division 2: Where ignitable concentrations of combustible dusts are not likely to exist under normal operating conditions. |
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Class II groups Division 1 and 2 |
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Class II temperature codes Division 1 and 2 T1 (≤ 450°C) T2 (≤ 300°C) T2A, T2B, T2C, T2D (≤ 280°C, ≤ 260°C, ≤ 230°C, ≤ 215°C) T3 (≤ 200°C) T3A, T3B, T3C (≤ 180°C, ≤ 165°C, ≤ 160°C) T4 (≤ 135°C) T4A (≤ 120°C) T5 (≤ 100°C) T6 (≤ 85°C) |
Class III
Ignitable fibers and flyings
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Class III area classification Division 1: Where easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used. Division 2: Where easily ignitable fibers are stored or handled. | |
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Class III groups Division 1 and 2 None. |
Class III temperature codes Division 1 and 2 None. |
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Note: Article 503 of the National Electric Code limits the maximum temperature for Class III equipment to 165°C for equipment not subject to overloading and to 120°C for equipment that may be overloaded. | |
Source: UL's Hazardous Locations Services
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