1. Purpose – This Article explains, for the contractor or equipment fabricator, the supplemental requirements to Engineering specification ( Installation and Testing of Medium Voltage Cable ) for Electrical work installation in Class I Hazardous Areas. Moreover here we will explain about electrical installations in hazardous locations Class I Areas and guide with PDF format as well as hazardous area classification drawing.
2. Scope
2.1 This article applies to all above-ground electrical equipment material and installations located in Class I Hazardous Areas as defined in the National Electrical Code (NEC).
2.2 Co-dependent Article
2.2.1 This article is not complete unless studied with the following article: Electrical Work.
3. Related Documents
3.1 Engineering Article for Reference
Electrical Work (Installation and Testing of Medium Voltage Cable)
Low Point Drain Installation Details
3.2 National Fire Protection Association (NFPA)
70 – National Electrical Code (NEC) – Latest Edition
4. General Notes for Hazardous Area Requirements for Class I Areas
4.1 All electrical equipment, fittings, and material provided by the contractor shall be listed and approved for the Class, Division, and Group of the area in which it is being installed, here in this article will be discussed Hazardous Area Requirements for Class I Areas only.
4.2 Flanged-type explosion-proof enclosures designed for hazardous duty areas shall be handled with extreme caution to avoid damage to machined surfaces. When the covers of such enclosures are removed, any scratching or gouging of mating surfaces must be avoided. Before reinstalling, the flange shall be checked and wiped clean of any dust or debris. All cover-fastening devices must be reinstalled to maintain enclosure integrity and torqued to the equipment manufacturer’s requirements.
5. Cnduits
5.1 All conduit shall be (RMC) rigid steel or rigid aluminum. Flexible metal conduit can be used in Division 2 areas. Explosion-proof, flexible metal conduit can be used for Division 1 areas (as defined by the NEC). Refer to project area classification drawing for area classification designations.
6. Electrical Boxes and Conduit Fittings
6.1 Use the appropriate explosion-proof pull boxes, terminal boxes, and equipment enclosures as required by the contract drawings (for example, Type EJB, GUB). Use the appropriate explosion-proof outlet, switch, and junction box, as well as the conduit fitting, as required by the contract drawings (for example, Type EAB for Group B, Type GUA for Groups C, D areas). All unused conduit openings must be closed using plugs approved for the area classification.
6.2 All cover screws and bolts intended to hold explosion-proof joints firmly together must always be tight when the circuits are energized. Since the substitution of other types of materials might weaken the assembly and render it unsafe, use only bolts or screws provided by the equipment manufacturer.
6.3 The contractor or equipment fabricator shall ensure that the installed orientations of all seal fittings are according to the manufacturer’s recommendation. Some models of seal fittings are only approved for installation in the vertical position.
6.4 The cross-sectional area of conductors permitted in a conduit seal, by the NEC, shall not exceed 25% of the allowable fill of the conduit entering the seal. This transition shall be accomplished by either using an approved seal fitting manufactured specifically to provide the 25% fill or by using a conduit seal with reducers that are larger than the conduit entering the seal and provides the required 25% fill by calculating the cross-sectional area of the conductors compared to the 25% cross-sectional area fill of the seal.
7. Equipment and Materials for Hazardous Area Requirements for Class I
7.1 Supplied equipment should be suitable for the area classification in which it will be installed; however if this is not the case, the Engineer must report any discrepancies to representative.
7.2 Furnished equipment and skids will be shipped to the site with unpoured conduit seals. When directed by the field representative, the field contractor shall pour the conduit seal fittings with the appropriate sealing compound per section 8.4.
8. Conduit and Cable Installation
8.1 A standard tapered thread have to provide a 3/4 in taper per ft to ensure a tight connection into a threaded conduit hub. All threaded joints shall be made up of at least five threads fully engaged and wrench tight. Running threads are unacceptable.
8.2 Myers hubs shall be used for each indoor conduit termination at sheet metal enclosures, pull boxes, and other similar locations, unless an appropriate conduit bonding jumper is present on the individual conduit. This applies not only to hazardous duty areas but also to all interconnected raceways, fittings, boxes between the hazardous duty area, and the service equipment (for example, main control center or switchgear).
8.3 The conduit system shall be arranged and provided with low point drains to prevent the accumulation of moisture. When this is not practical, combination drain seal fittings shall be used to prevent water accumulation above a seal. Refer to LOW POINT DRAIN INSTALLATION DETAILS for recommended low point drain installation details.
8.4 Conduit seal fittings must be placed to permit the installation of sealing compound after the wiring is completed. Only compounds specifically approved for the fitting by the fitting manufacturer may be used and the fitting must be filled to a depth of not less than the trade size of the conduit and never less than 5/8 inch. Before placement of sealing compound in any fitting, circuit checkout must be completed and confirmed by the field representative.
8.4.1 Cables entering enclosures that are required to be explosion proof shall be sealed for Hazardous Area Requirements for Class I Areas. When run in conduit all type TC and PLTC cables shall have their outer jacket and other coverings removed to expose the individual conductors. Individual insulated conductors shall be separated to allow sealing compound to surround each individual insulated conductor and the outer jacket within the seal fitting. For shielded cables and twisted pair cables it shall not be required to remove the shielding material or separate the twisted pair.
8.4.2 Conduit seals as required by code shall be installed at hazardous area boundaries. Type TC and PLTC cables do not need to have the outer jacket removed unless the cable is terminated in process equipment that may cause pressure in the cable. See NEC 501.15 for more information about Hazardous Area Requirements for Class I Areas.
8.5 The field engineer shall visually inspect all conduit seals to confirm that seals have been filled with sealing compound. After the visual inspection is completed, the technician shall paint the fitting with black paint to provide visual indication that seal has been filled.
8.6 For Maintenance purpose, A conduit union is required between the seal and any device with a fixed hub that may require removal of the device.
8.7 Where cable fittings are required to sealed, Sealing Installation shall as per the manufacturer’s instructions. Field Engineer or Inspector shall inspect and approve Completed connector installations.
9. Hazardous Area Requirements for Class I Wiring
9.1 No splices are permitted in conduit seal fittings.
Here is video to explain about hazardous area classification chart.