If fire or explosion hazards exist in a location because of flammable gases or vapors, flammable liquids, combustible dust, or ignitible fibers or flyings, the location is described as a hazardous (classified) location. Details on how the electrical classification locations are determined for a given installation are provided in EEX 208, Design Criteria for Hazardous Areas. NEC (NFPA 70) describes these locations with three separate classifications: Class I, Class II, and Class III. A Class I hazardous classification is used to describe a location where flammable gases or vapors are or may be present in quantities that are sufficient to produce explosive or ignitible mixtures in air.
A Class II hazardous classification describes a location where fire or explosion hazards may exist because of the presence of combustible dusts in air. A Class III hazardous classification describes a location where fire or explosion hazards may exist because of the presence of ignitible fibers or flyings in air.
Each of the three classifications of hazardous locations (Class I, Class II, and Class III) can be broken down further into a Division 1 location or a Division 2 location (i.e., an area might be given a Class I, Division 1 classification). A Division 1 classification implies that danger is imminent at any or all times during the course of normal operation. A Division 2 classification implies that danger is not present under normal conditions but is likely to arise from some reasonable, foreseeable, accidental occurrence.
For Saudi Aramco installations, a nonclassified location is defined as follows:
o A location that is completely outside of a Class I, Division 1 or Division 2 location.
o An enclosed space that is within a Class I, Division 1 or Division 2 location, does not contain a release source, and is pressurized or purged by an inert gas or by air that is taken from an unclassified location that complies with Type X or Type Z purging. Purging is defined as the process of supplying an enclosure with clean air or an inert gas to displace the atmosphere that is currently within the
This section of the Module presents the wiring and sealing requirements that must be met for Saudi Aramco above-grade installations. The sections that follow discuss the requirements that must be met for Saudi Aramco above-grade installations in terms of wiring, conduit sealing, and cable sealing.
Wiring
Various resources state the specific requirements that wiring must meet when it is placed in hazardous locations in Saudi Aramco above-grade installations. The resources that are applicable to Saudi Aramco hazardous installations include the following:
o SAES-P-100 (Basic Power System Design Criteria) o NEC (NFPA 70) (The National Electrical Code)
The various NFPA-70 and Saudi Aramco requirements that must be met for the wiring methods that are used in above-grade installations for Class 1, Division 1 and Class 1, Division 2 hazardous locations are as follows:
Rigid-steel conduit is specified for Class 1, Division 1 hazardous locations, or where exceptional mechanical protection is required.
Threaded rigid-metal conduit or type MI cable with termination fittings that are approved for the location should be used. In Class 1, Division 1 locations, Crouse-Hinds-type EC series flexible conduit or an equivalent type of flexible conduit should be used.
All boxes, fittings, and joints should be threaded for connection to conduit or cable terminations and should be explosionproof.
Threaded joints should be made up with at least five threads fully engaged. Type MI cables should be installed and supported in a manner to avoid tensile stress at the termination fittings. Flexible fittings (when required) should be approved for use in Class 1 locations.
For Class 1, Division 1 locations, flameproof enclosures (Ex d II) are permitted when the following conditions are met:
o All cables enter the enclosure through rigid-steel conduit that has approved sealing fittings.
o The overall enclosure not just its components is flameproof (Ex d II explosionproof) as a whole.
For Class 1, Division 2 hazardous locations, cable tray is the preferred method of power distribution in unclassified areas.
Threaded rigid-metal conduit or type MI, MC, MV, TC, or SNM cable with approved termination fittings (in cable tray) should be used. To avoid tensile stress to the conductors, cable in cable tray should be installed at the termination fittings. Boxes, fittings, and joints are not required to be explosionproof in Class 1, Division 2 locations except under the following conditions:
o Switches, circuit breakers, and the make-and-break contacts of pushbuttons, relays, alarm bells, and horns should meet the requirements that are specified for Class 1, Division 1 locations (see above). General purpose
enclosures are permitted, however, if the current interrupting contacts are hermetically sealed against the entrance of gases or vapors, or are in circuits that do not release sufficient energy to ignite a specific ignitable atmospheric mixture under normal circumstances.
o Circuit breakers, motor controllers, and switches that are intended to interrupt current in the normal performance of their function should be provided with enclosures that are approved for Class 1, Division 1 locations. However, general purpose enclosures can be used if the interruption of current occurs in a hermetically-sealed chamber, if the make and break contacts are immersed in oil, or if the interruption of current occurs in a factory-sealed
explosionproof chamber that is approved for the installation.
When provisions must be made for limited flexibility, flexible metal fittings should be used. In Class 1, Division 2 locations, flameproof enclosures (Ex d II) and increased safety apparatus (Ex e II) are permitted.
In addition to the specific requirements for wiring methods that were listed above, the equipment that is used in hazardous locations and that is required by NEC (NFPA 70) to be approved (except for conduit sealing fittings) are required to be UL-labeled, listed, or certified. Any of the following organizations may be used to meet labeling, listing, or certifying requirements:
o USA Underwriters Laboratories, Inc. (UL) labeled or listed, or Factory Mutual Research
Corporation (FM) certified.
o Canada Canadian Standards Association (CSA) certified.
o UK British Approvals Services for Electrical Equipment in Flammable Atmospheres (BASEEFA) certified.
o France Centre d'Etudes et Rechereches de Charbonnages de France (CHERCHAR) certified.
o Germany Physikalisch Technische Bundesanstalt (PTB) certified.
o Switzerland Schweizerischer Elektrotechnischer Verein (SEV) certified.
o Italy Centro Elettrotecnico Sperimentale Italiano (CESI) certified.
The labeling, listing, or certification of electrical equipment in hazardous locations should be based on the latest version of the following standards and procedures:
o UL 886 (Outlet Boxes and Fittings for Use in Hazardous-Classified-Locations).
o FM procedures.
o CSA standards.
o CENELEC EN 50 014 and EN 50 018 (for flameproof enclosures Ex d II) or EN 50 014 and EN 50 019 (for increased safety apparatus Ex e II).
Conduit Sealing
In a horizontal conduit run, a differential pressure could cause flammable gases to be transmitted from a classified area to an unclassified area through the conduit system. In a vertical conduit run, gas vapors can move through a conduit system without a pressure differential. Conduit seals are used to prevent the passage of flammable gases through the conduit system, and they are also used to prevent the passage of flames from one portion of the electrical installation to another portion of the electrical installation through the conduit system. Conduit seals are made by filling a specialized sealing fitting with a sealing compound.
The resources that describe the conduit sealing requirements that should be met for Saudi Aramco above-grade hazardous installations are listed as follows:
o SAES-P-104 (Wiring Methods and Materials)
o SAES-J-902 (Electrical Systems for Instrumentation) o NEC (NFPA 70) (The National Electrical Code)
Specific NEC (NFPA 70) and Saudi Aramco requirements for conduit sealing in Class I hazardous areas are outlined in the following paragraphs.
When conduit seals are used (for both classified and unclassified locations), some general requirements must be met. For Class 1 and nonclassified locations, wire fill of standard conduit sealing fittings should not exceed 25 percent based on the size of the conduit. Explosionproof seals should be used only when required by NEC (NFPA 70). Each conduit that enters a process unit control house should be sealed outside at the point of entry for an above-grade conduit run. When conduit seals are required, the seals should be located within 450 mm (18 inches) of an enclosure. Vertical or horizontal conduit runs that require sealing should be sealed with combination vertical/horizontal seals (Type EYS or equivalent). A conduit run that crosses hazardous location boundaries below ground must be sealed at both ends of the conduit that emerge from the ground.
For Class 1, Division 1 locations, seals are required when conduit runs enter an enclosure for switches, circuit breakers, fuses, relays, resistors, or other apparatus that may produce arcs, sparks, or high temperature. Fittings that are installed between the seal and the enclosure must be explosionproof. Seals are required when conduit that is of 2-inch size or larger enters an enclosure or fitting that houses terminals, splices, or taps.
A seal is required in each conduit run that leaves the Class I, Division 1 area. The seal can be placed on either side of the area boundary, but it should be designed and installed to minimize the amount of gas or vapor that passes through the boundary in the conduit. No unions, couplings, boxes, or fittings are allowed in the conduit between the sealing fitting and the point at which the conduit leaves the Class I, Division 1 area. Metal conduit that does not have unions, couplings, boxes, or fittings and that passes completely through a Class 1, Division 2 area with no fittings less than 305 mm (12 inches) beyond each boundary is not required to be sealed if the termination points of the unbroken conduit are in nonclassified locations.
For Class 1, Division 2 locations, seals are required for connections to explosionproof enclosures. Seals are required in each conduit that passes from a Class 1, Division 2 location into a nonclassified location. The seal can be placed on either side of the boundary, but it should be designed and installed to minimize the amount of gas or vapor that may have entered the conduit system from the Class 1, Division 2 area from being communicated to the conduit that is beyond the seal. Rigid-metal conduit should be used between the sealing fitting and the point at which the conduit leaves the Division 2 area, and a threaded connection should be used at the sealing fitting. Unions, couplings, boxes, or fittings are not allowed in the conduit between the sealing fitting and the point at which the conduit leaves the Class 1, Division 2 area.
If the termination points of the unbroken conduit are in nonclassified locations, metal conduit that contains no fittings, boxes, couplings, or unions and that passes completely through a Class 1, Division 1 location with no fittings less than 305 mm (12 inches) beyond each area boundary is not required to be sealed.
Conduit systems that terminate at an outdoor nonclassified location where a transition is made to cable tray or type MI cable is not required to be sealed where the conduit system passes from the Class 1, Division 2 area into the non-classified area. The conduits should not terminate in an enclosure that contains an ignition source.
Conduit sealing fittings that are used in Class I hazardous areas should be constructed so that sealing compound can be pushed deep into the conduit sealing fitting. The minimum depth of the sealing compound should be equal to but not less than the internal diameter of the conduit. The depth of the sealing compound should never be less than 15.9 mm (5/8 inches) at any point between the conduit openings. In conduit sealing fittings that are used for vertical mounting, the required depth of the sealing compound should be measured from the top of the lower conduit stop and the lowest edge of the tapped opening for introducing the sealing compound into the conduit sealing fitting.
The construction of the conduit sealing fitting should provide a tight seal and retain the sealing compound in place. The sealing compound should form a permanent seal under service conditions and should not be adversely affected by the hazardous vapors of the location in which the sealing compound will be used. When an opening is used for the introduction of the sealing compound into the conduit, a plug that has at least five full tapered threads is considered satisfactory for closing the opening.
Conduit sealing fittings are required to be labeled, listed, or certified by Underwriters Laboratories, Inc. (UL), Factory Mutual Research Corp. (FM), or the Canadian Standards Association (CSA). The labeling, listing, or certification of electrical equipment in hazardous locations should be based on the latest version of the following standards and procedures:
o UL 886 (Outlet Boxes and Fittings for Use in Hazardous-Classified-Locations).
o FM procedures.
o CSA standards.
o CENELEC EN 50 014 and EN 50 018 (for flameproof enclosures EEX D II), or EN 50 014 and EN 50 019 (for increased safety apparatus EEX E II).
Cable Sealing
In addition to conduit seals, the NEC (NFPA 70) has requirements for cable seals. Conduit seals are used to prevent the passage of gases through the conduit around cables or single conductors.
Cable seals are used to prevent the passage of gases through multiple-conductor cables. Seals that are installed in Class I hazardous areas are intended to prevent the passage of flammable gases or flames from one portion of an electrical installation to another portion of the electrical installation. Seals in Class II hazardous areas are intended to prevent combustible dust from entering an otherwise dust-tight enclosure.
Multiple-conductor cables are considered to be similar to a conduit system that contains several insulated conductors. In addition to the spaces between the strands of the individual conductors, there may be spaces between the individual conductors of a cable (referred to as the cable core). The cable core may be filled in or it may be relatively open. If the cable core is constructed so that it performs the function of a conduit seal, the cable can be considered to be incapable of passing gases or vapors through its core and will be so designated.
The NEC (NFPA 70) and UL requirements for cable sealing fittings are somewhat similar to those requirements that are listed in the previous section for conduit sealing fittings. The requirements that must be met for Saudi Aramco above-grade hazardous installations are as follows.
For Class 1, Division 1 locations, each multiple conductor cable in conduit is considered as a single conductor if the cable is incapable of transmitting gases or vapor through the cable core.
These cables should be sealed under the same conditions as the conditions that were stated for conduit seals in Class 1, Division 1 areas.
Cables that have a gas/vapor-tight continuous sheath that are capable of transmitting gases or vapors through the cable core should be sealed if they are located in a Division 1 location. The cables are sealed after the jacket and any other coverings are removed so that the sealing compound will surround each individual insulated conductor and the outer jacket.
For Class 1, Division 2 locations, cable seals are required for cables that enter enclosures that are required to be approved for Class I locations, and the cables should be sealed at the point of entrance to the enclosure.
Multiple-conductor cables that have a gas/vapor-tight continuous sheath should be sealed with an approved fitting if they are located in a Division 2 area. The cables are sealed after the jacket and any other covering has been removed so that the sealing compound will surround each individual insulated conductor in a manner that will minimize the passage of gases and vapors.
Cables that have a gas/vapor-tight continuous sheath and that will not transmit gases or vapors through the cable core in excess of the quantity that is permitted for the seal fitting are not required to be sealed except at the entrance of enclosures that are required to be approved for Class 1 locations. The minimum length of the cable run should not be less than the length that limits gas or vapor flow through the cable core to the rate that is permitted for seal fittings. The permitted rate for seal fittings is 198 cubic centimeters per hour of air that is at a pressure 1493 Pascals (0.007 cubic feet per hour of air that is at a pressure of 6 inches of water).
Cables that have a gas/vapor-tight continuous sheath should not be required to be sealed except at the entrance of enclosures that are required to be approved for Class I locations. If the cable is attached to process equipment or devices that can cause a pressure in excess of 1493 Pascals (6 inches of water) to be exerted at the cable end, the cable should be sealed. If the pressure exerted at the ends of the cable exceeds 1493 Pascals, however, a seal, barrier, or other method should be provided to prevent the passage of flammables into an non-classified area.
Cables that have an unbroken gas/vapor-tight continuous sheath should be permitted to pass through a Class 1, Division 2 location without seals. Cables that do not have a gas/vapor-tight continuous sheath should be sealed at the boundary of the Division 2 and nonclassified location in such a manner as to minimize the passage of gases or vapors into a nonclassified location.