Main keywords for this article are Class I, Division 1, Hazardous Locations, Class I, Division 2, Sealing (NFPA 70, Article 502), Fittings and boxes, NEC Wiring in Process Industry.
NEC Wiring in Process Industry
General-purpose Locations (Dry and Nonhazardous)
Outlet boxes and equipment enclosures are constructed of sheet metal. Conduit ends are secured to the outlet boxes and equipment enclosures with threaded locknuts and bushings.
The other option is to use open ended conduit installation system. Unsupported cable shall be kept to a minimum and distances from the open ended conduit shall not exceed 400mm. The open end of the conduit shall be sealed with the sealing compound. Where there is possibility of mechanical damage to unsupported cable, additional metallic guards shall be provided.Entry into outlet boxes, junction boxes or equipment enclosures shall be via appropriate cable glands.
Conduit fittings are usually threaded-hub type with sheet-metal covers and no gaskets. Conduit should usually be rigid galvanized steel (RGS). However, electrical metallic tubing (EMT) or intermediate metallic conduit (IMC) may be used in non-hazardous locations for building interior and exterior wiring, where it is sheltered from rain.
Dusty Nonhazardous Locations and Class III, Division 2, Hazardous Locations
Conduit shall be type RGS. Outlet boxes and equipment enclosures are equipped with gasketed covers. Conduit ends are secured to outlet boxes and equipment enclosures with threaded locknuts, bushings, and neoprene or polyethylene washer. Conduit fittings are threaded-hub type with gasketed sheet-metal covers. If open ended conduit installation method is used, it shall be installed as per requirements in above.
Damp and Wet and Slightly Corrosive Locations
Conduit shall be type RGS. All conduit joints are threaded and screwed tight to make a watertight system. All joints are protected against corrosion by coating the threads with aluminum or graphite bearing paint or compounds. There should be a minimum of a 6.35 mm (1/4 in) air space between the conduit and the wall or other supporting structure (NFPA 70, Article 300). All boxes and equipment enclosures are made of cast metal or heavy sheetmetal construction with gasketed covers. Threaded hubs are used for conduit entrances or they are made rain-tight by other means. Provisions are made at the lowest point, or points, of the conduit system for draining off condensation in wet locations.
Highly Corrosive Locations
PVC coated RGS conduit shall be used with PVC coated junction, boxes and fittings. Boxes made of plastic or fiberglass may be used with company approval. Junction boxes shall be stainless steel. Provisions are made at the lowest point, or points, of the conduit system for draining off condensation in wet locations.
Class I, Division 1, Hazardous Locations
- Wiring method (NFPA 70, Article 501) shall be:
a. Threaded RGS conduit with joints having a minimum of five full threads engaged.
b. Flexible connections installed only where necessary. Only approved explosion-proof types for Class I locations shall be used.
c. Flexible cords (NFPA 70, Article 501) used only for connection of portable lamps or portable appliances. All such cords shall:
i. Be of a type approved for extra hard usage
ii. Contain a grounding conductor in addition to the circuit conductors, and shall be connected in accordance with NFPA 70 Article 501
iii. Be supported by clamps or other suitable means in a way that there will be no tension on terminal connections
iv. Be provided with suitable seals where the cord enters boxes, fittings, or enclosure of the explosion-proof type
d. Underground wiring installed in rigid metal conduit or, if buried 600 mm or more, may be installed in nonmetallic conduit or duct
- Fittings and boxes (NFPA 70, Article 501) shall be threaded-hub type with a minimum of five full threads engaged, and shall be of approved explosion-proof type for Class I locations.
- Sealing (NFPA 70, Article 501)
a. Conduit shall be sealed in accordance with NFPA 70 Article 501 to prevent the propagation of flame from one part of the system to another.
b. Where the conduit comes from a hazardous location, the first fitting after a conduit emerges from a concrete slab or from underground, a seal fitting shall be installed, whether or not the conduit emerges in a hazardous location. - Drainage (NFPA 70, Article 501). Approved fittings shall be provided at the lowest point, or points, of the conduit system for draining off condensation in wet hazardous locations.
Class I, Division 2, Hazardous Locations
- Wiring method (NFPA 70, Article 501) shall be:
a. Threaded rigid metal conduit
b. Enclosed gasketed busways
c. Type MC, MV, TC, ITC or IEC equivalent cable with approved termination fittings. Type PLTC or IEC equivalent for power limited signaling circuits. See SES E22-S01 and E22-S02 for NEC and IEC type equivalent cable construction.
d. Flexible metal conduit has only a limited approved application, for example for motor connections and other equipment where some adjustment in location is necessary, to accommodate equipment vibration and for connections to field mounted process instruments. Liquid tight flexible-metal conduit shall be used in wet and corrosive locations.
e. Flexible metal conduit shall not be used in Division 1 hazardous locations
f. Flexible cord requirements are the same as those for flexible cords in Type E installations (NFPA 70, Article 501)
g. For cable installations in cable trays, see NFPA 70, Article 318 and 7.3.1 of this standard regarding installation limitations. Where trays pass through walls from a hazardous area to a non hazardous area, or through floors, the entire opening shall be effectively sealed after cables are installed.
h. Underground wiring shall be installed in rigid metal conduit, or direct buried 600 mm or more, installed in nonmetallic conduit or duct if enclosed in concrete .
i. Armored cable may be direct buried in areas not subject to vehicular traffic. It shall be buried a minimum of 600 mm, surrounded by a 300 mm thick layer of thermal sand (Rho = 120). The top of the thermal sand shall be covered with 150 mm thick red concrete or red concrete tiles. Back fill to grade with native soil. - Fittings and Boxes
a. Fittings, boxes, and equipment enclosures need not be approved explosion proof type except at arcing devices (NFPA 70, Article 501). Conduit terminations shall be made to the box body as permitted by the NFPA 70. Where double lock nut type of conduit terminations are permitted, bonding jumpers from the box body to the conduit shall be provided.
b. Connectors for ordinary flexible conduit terminations and for connecting the flexible conduit to rigid conduit shall be as specified in NFPA 70, Article 350. Connectors for liquid tight flexible conduit shall be as specified in NFPA 70, Article 351. - Sealing (NFPA 70, Article 501)
a. Conduits shall be sealed at all enclosures which are required to be explosion-proof and where conduit runs pass from the Class I, Division 2, hazardous locations into a non hazardous location (see NFPA 70, Article 501).
b. The first fitting after a conduit emerges from a concrete slab or from underground shall be a sealing fitting. - Drainage (NFPA 70, Article 501).The same provisions shall apply as those for Type E installations, except that approved explosion-proof fittings shall be required only at approved explosion-proof housings.
Class II, Division 1, and Class III, Division 1, Hazardous Locations
- Wiring method (NFPA 70, Article 502 and, Article 503) shall be:
a. Threaded rigid conduit. For Class III, Division 1, electrical metallic tubing, nonmetallic conduit, or dust-tight wireways may be used.
b. Type MI (mineral-insulated) cable requirements shall be the same as for Type E installations, for example approved type termination fittings.
c. For Class III, Division 1, MC cable may be used with approved fittings
d. Flexible metal conduit shall be used in limited applications only, for example at motor terminals and other equipment where some adjustment in location is necessary. Liquid tight flexible conduit may be used except where dusts are of an electrically conducting nature. Bonding jumpers shall be provided across flexible conduit sections (see NFPA 70, Articles 502 and 503). Where dusts are of an electrically conducting nature, flexible cords with dust-tight seals at both ends shall be used. Cords shall have an additional conductor for grounding. Approved dust-ignition-proof flexible couplings may also be used, and shall not require a bonding jumper. - Fittings and boxes (NFPA 70, Article 502 and, Article 503)
a. All fittings and boxes shall be threaded hub or threaded boss type for connection to conduit or cable terminations; have close-fitting covers and shall have no openings, for example holes for attachment screws, through which dust might enter, or through which sparks or burning material might escape. Fittings and boxes in which taps, joints, or terminal connections are made, or which are in locations where the dusts are of an electrically conducting nature, shall be approved dust-ignition proof type for Class II locations. Conduit terminations shall be made in accordance with NFPA 70, Article 502 and Article 503.
b. Connectors for liquid tight flexible conduit terminations and for connecting the flexible conduit to rigid conduit shall be approved for that application. - Sealing (NFPA 70, Article 502)
a. Where a raceway provides communication between a non dust-tight fitting or enclosure and one which is required to be approved, dust-ignition-proof for Class II locations, three alternative methods may be used to prevent the travel of dust through the raceway to the dust-tight enclosure:
(i) A permanent and effective seal
(ii) A horizontal section of raceway which is not less than 3 m long, or
(iii) A vertical section of raceway extending downward from the dust-tight enclosure, which is not less than 1.5 m long
b. Seals can be provided using any of the seal fittings designed for Class I locations (see NFPA 70, Article 501).
Class II, Division 2, Hazardous Locations
- Wiring method (NFPA 70, Article 502) shall be:
a. RGS conduit
b. Type MI may be used with SABI C approval
c. MC (with approved term ination fittings). Type PLTC, ITC or TC cable may be installed in ventilated channel-type cable trays in a single layer with a space not less than the larger cable diameter between the two adjacent cables.
d. Flexible metal conduit requirements shall be the same as for Type G installations
e. Flexible cord requirements shall be the same as for Type G installations - Fittings and boxes (NFPA 70, Article 502)
a. All fittings and boxes in which taps, joints, or terminal connections are made shall be provided with telescoping or close-fitting covers, or other effective means for example cover gaskets, to prevent the escape of sparks or burning material. Such fittings shall have no openings, for example holes for attachment screws, through which, after installation, sparks or burning material might escape, or through which adjacent combustible material might be ignited. Conduit terminations shall be made in accordance with NFPA 70, Article 502. Where the double locknut type of conduit terminations are permitted, bonding jumpers from the box body to the conduit shall be provided.
b. For conduit entrances for electrical metallic tubing, see NFPA 70, Article 502. Couplings shall be compression type.
c. Connections for liquid tight flexible conduit terminations, and for connecting flexible conduit to rigid conduit, shall be approved fittings in accordance with NFPA 70, Article 502. - Sealing. Sealing requirements shall be the same as for Type G (NFPA 70, Article 502).
NEC Wiring System Types & NEC Wireway Systems in Plant Industry