In humid atmospheres or in wet locations where it is likely that water can enter the interiors of enclosures or raceways, the raceways should be inclined so that water will not collect in enclosures or on seals but will be led to low points where it may pass out through drains. Frequently the arrangement of raceway runs makes this method impractical if not impossible. In such instances, drain sealing fittings shall be used. These fittings prevent accumulations of water above the seal. [See NEC 501-5(d).]

In locations usually considered dry, surprising amounts of water frequently collect in conduit systems. No conduit system is airtight; therefore, it may breathe. Alternate increases and decreases in temperature and barometric pressure because of weather changes or the nature of the process carried on in the location where the conduit is installed will cause breathing. Outside air is drawn into the conduit system when it breathes in. If this air carries sufficient moisture, it will be condensed within the system when the temperature decreases and chills the air. With internal conditions being unfavorable to evaporation, the resultant water accumulation will remain and be added to by repetitions of the breathing cycle. In view of this likelihood, it is good practice to ensure against such water accumulations and probable subsequent insulation failures by installing drain sealing fittings with drain covers or inspection covers even though conditions prevailing at the time of planning or installing may not indicate the need.

5.4.1.3 SELECTION OF SEALS AND DRAINS

Different types of seals and drains are made to be used for vertical or horizontal installations and are to be used only for the purpose for which they were designed. Care shall be taken when selecting and installing such fittings.

5.4.1.3.1 PRIMARY CONSIDERATIONS

The following primary considerations should be used when selecting seals and drains:

1. Select the proper sealing fitting for the hazardous vapor involved (i.e., Class I Groups A, B, C, or D).

2. Select a sealing fitting for the proper use in respect to mounting position. This is particularly critical when the conduitruns between hazardous andnonhazardous areas. Improper positioning of a seal may permit hazardous gases or vapors to enter the system beyond the seal and to escape into another portion of the hazardous area or into a nonhazardous area. Some seals are designed to be mounted in any position; others are restricted to horizontal or vertical mounting.

3. Install the seals on the proper side of the partition or wall as recommended by the manufacturer.

4. Only trained personnel should install seals in strict compliance with the instruction sheets furnished with the seals and sealing compound. Precautionary notes should be included on installation diagrams to stress the importance of following manufacturer's instruction.

5. NEC 501-5(c)(4) prohibits splices or taps in sealing fittings.

6. Sealing fittings are listed by UL for use in Class I hazardous locations with sealing compound only. This compound, when properly mixed and poured, hardens into a dense, strong mass, which is insoluble in water, is not attacked by chemicals, and is not softened by heat. It will withstand with ample safety factor the pressure of exploding trapped gases or vapor.

7. Conductors sealed in the compound may be approved thermoplastic or rubber insulated type. Both may or may not be lead covered (the lead need not be removed).

Caution: Sealing compounds are not insulating compounds; therefore, they shall not be used as such.

5.4.1.3.2 TYPES OF SEALING FITTINGS

Sealing fittings meet the requirements of NEC when properly installed.

A certain style of sealing fittings are for use with vertical or nearly vertical conduit in sizes from 1/ 2 through 1 in. Other styles are available in sizes 1/2 through 6 in. for use in vertical or horizontal conduits. In horizontal runs, these are limited to face up openings. Sizes from 1-1 /4 through 6 in. have extra-large work openings and separate filling holes so that fiber dams are easy to make. Overall diameter of sizes 1-1/4 through 6 in. is scarcely greater than that of unions of corresponding sizes, permitting close conduit spacings. Other style seals are for use with conduit running at any angle, from vertical through horizontal.

5.5 MANUFACTURERS' DIGEST

Manufacturers produce NEC code digests for selection of seals and drains and provide, by class and division, catalog data and installation diagrams for their use in electrical power and lighting systems in hazardous areas. The manufacturers' NEC code digests should be in compliance with current NFPA/NEC requirements. The two that are most used are as follows:

1. Crouse-Hinds ECM Code Digest

2. Appleton's NEC Code Review.

5.6 DESCRIPTIONS, FEATURES, AND TEST CRITERIA OF ENCLOSURES FOR HAZARDOUS (CLASSIFIED) LOCATIONS (PER NEMA 250)

Type 7 and 10 enclosures, when properly installed and maintained, are designed to contain an internal explosion without causing an external hazard. Type 8 enclosures are designed to prevent combustion through the use of oil-immersed equipment. Type 9 enclosures are designed to prevent the ignition of combustible dust.

As mentioned earlier, hazardous locations (other than in mines) are classified according to the flammability or combustibility of the materials that may be present and also according to the likelihood that a flammable or combustible concentration is present. Fordefmitions and classifications, see the NEC, Article 500, and NFPA 497M, "Classification of Gases, Vapors and Dust for Electrical Equipment in Hazardous Classified Locations." Descriptions and tests in this standards publication cover equipment that is suitable forinstallation in locations classified as Division 1 or 2. In Division 2 locations, other types of protections and enclosures for nonhazardous locations may be installed if the equipment does not constitute a source of ignition under normal operating conditions. See the specific sections of Articles 501 through 503 of the NEC.

Intrinsically safe equipment (not capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of specific hazardous atmospheres) may be installed in any type of enclosure otherwise suitable for the environmental conditions expected. See ANSI/ UL 913, "Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, 11, III, Division I, Hazardous (Classified) Locations" for detailed requirements.

Purged and pressurized equipment should be installed in enclosures suitable for nonhazardous locations. Hazards may be reduced or eliminated by adequate positive pressure ventilation from a source of clean air in conjunction with effective safeguards against ventilation failure. See NFPA 496, "Purged and Pressurized Enclosures for Electrical Equipment in

Hazardous Locations" for detailed requirements.