Note: The source of the technical material in this volume is the Professional
Engineering Development Program (PEDP) of Engineering Services.
Warning: The material contained in this document was developed for Saudi
Aramco and is intended for the exclusive use of Saudi Aramco’s employees. Any material contained in this document which is not already in the public domain may not be copied, reproduced, sold, given, or disclosed to third parties, or otherwise used in whole, or in part, without the written permission of the Vice President, Engineering Services, Saudi Aramco.
Saudi Aramco DeskTop Standards
EVALUATING ABOVE-GRADE WIRE,
CABLE, AND CONDUIT INSTALLATIONS
ABOVE-GRADE INSTALLATION TECHNIQUES: CONDUIT, CABLE TRAYS, AND EXPOSED CABLE ... 5
Conduit ... 5
Rigid Steel ... 6
EMT ... 7
Flexible Liquid-Tight... 8
Cable Trays: Design, Construction, and Usage Requirements... 8
Fiberglass ... 10
Exposed Cable: Uses and Routing Requirements... 11
Routing Requirements ... 12
DETERMINING CABLE TRAY INSTALLATION REQUIREMENTS... 13
Magnetic Heating Effects... 18
Circuit Separation ... 19
Grounding and Bonding Requirements and Methods... 22
Tray Separation ... 23
Tray Routing/Protection Covers... 26
Fittings, Bends, and Drops ... 27
DETERMINING CONDUIT INSTALLATION REQUIREMENTS... 28
Conduit Types and Applications ... 28
Jam Ratio... 32
Cable Clearance Within the Conduit ... 33
Magnetic Heating Effects ... 34
Conduit Clearances ... 34
Fire Proofing ... 34
Conduit Bending ... 35
Minimum Bending Radii ... 35
Conduit Threading ... 36
Indoor and Outdoor Conduit Terminations ... 38
Fittings ... 38
Seals (Explosion Proof) ... 39
Expansion Joints... 40
Conduit Supports... 40
DETERMINING CABLE PULLING REQUIREMENTS ... 43
Rigging Procedures ... 43
Pulling Grips ... 47
Pulling Lines ... 48
Duct Lubricating... 49
Cable Pulling Parameters ... 50
Maximum Pulling Tensions ... 50
Sidewall Pressure ... 64
Rigging Method Effects Calculation ... 68
DETERMINING HAZARDOUS AREA WIRING AND SEALING REQUIREMENTS ... 73
Wiring ... 74
Conduit Sealing ... 77
Figure 1: Aluminum Cable Tray Load/Span Class Designation (from NEMA VE-1) ... 15
Figure 2: Fiberglass Cable Tray Load/Span Data (from NEMA FG-1) ... 16
Figure 3: Fiberglass Cable Tray Temperature Correction for Allowable Working Load (from NEMA FG-1)... 17
Figure 4: Minimum Circuit Separation Distances for Signal Cabling in Cable Tray (from SAES-J-902) ... 21
Figure 5: Conduit Sizing Requirements... 31
Figure 6: Allowable Percentage of Conduit Fill (from NEC, Chapter 9) ... 32
Figure 7: Required Dimensions of Conduit Threads (from UL 6) ... 37
Figure 8: Maximum Distance Between Rigid-Metal Conduit Supports ... 42
Figure 9: Dynamometer Used to Measure Pulling Tension ... 45
Figure 10: Basket Grip on Cable ... 47
Figure 11: Pulling Eye on Cable ... 48
Figure 12: Cable Configurations... 53
Figure 13: Vertical Conduit Bends... 59
Figure 14: Example Pulling Tension Calculation... 61
Figure 15: Sidewall Pressure on Cable During a Pull... 65
Figure 16: Inside Radius of Standard Conduit Elbows... 67
In order to evaluate various types of approved Saudi Aramco above-grade wire, cable, and conduit installations for applicability of use, the Participant must have a thorough understanding of the types of installation techniques that are available, the minimum requirements of the various governing documents for each type of installation, and the methods that are used to determine the installation requirements for each type of installation.
The cable installation methods that are described in this Module (e.g., cable trays and above-ground conduit) are all used for the same reason: to install cable so that the cable will function safely and adequately throughout its projected operating life. As such, the optimal cable installation method should be selected for the facility installation. The optimal cable installation method is selected through an evaluation of the specific cable installation requirements, installation topography, and the installation method cost. In addition to the above-grade cable installation methods that are outlined in this Module, the below-ground cable installation methods that are covered in EEX 206.03 should also be considered.
This Module provides information on the following topics that are pertinent to evaluate above-grade wire, cable, and conduit installations for applicable use:
o Above-grade Installation Techniques: Conduit, Cable Trays, and Exposed Cable.
o Determining Cable Tray Installation Requirements o Determining Conduit Installation Requirements o Determining Cable Pulling Requirements
o Determining Hazardous Area Wiring and Sealing Requirements
ABOVE-GRADE INSTALLATION TECHNIQUES: CONDUIT, CABLE TRAYS, AND EXPOSED CABLE
There are several different installation techniques that can be used to install above-grade cable in Saudi Aramco facilities. Cable can be installed in an enclosed channel (raceway), an open channel (cable tray), or simply exposed to the elements. Rigid metal (bus ducts) can also be used to conduct electricity over short distances, but this method is limited and is not covered in this course. The selected installation method is to a large degree a matter of the Proponent's preference, however, the installation must comply with the applicable Saudi Aramco Engineering Standard (SAES).
Standards, in the title Saudi Aramco Engineering Standards
(SAESs), is a term that refers to the minimum mandatory requirements for the design, construction, maintenance, and repair of equipment and facilities for Saudi Aramco.
This section of the Module describes the following above-grade installation techniques:
o Cable Trays: Design, Construction, and Usage Requirements
o Exposed Cable: Uses and Routing Requirements Conduit
A conduit is defined as a metallic or nonmetallic tube that is used to protect electric wires and cables. Although there are various types of nonmetallic conduit systems that are available for use, Saudi Aramco allows only metallic-type conduit systems to be used for above-grade conduit installations. The types of conduit that are used in Saudi Aramco above-grade installations are rigid steel, electrical metallic tubing (EMT), and flexible liquid-tight. Due to the nature of Saudi Aramco cable installations (e.g., the cable use and installation environment), intermediate metallic conduit (IMC) is prohibited in all areas. Saudi Aramco considers the additional cost of rigid steel conduit to be worth the added protection that rigid steel offers over IMC.
Rigid-steel conduit is medium-thickness water pipe that has been reamed out to eliminate burrs and rough edges. Hot-dipped, galvanized, rigid-steel conduit is specified for all Saudi Aramco installations in which rigid-steel conduit is used; hot-dipped, galvanized, rigid-steel conduit is rigid-steel conduit that has been dipped in molten zinc during the forming process. Rigid-steel conduit is manufactured in standard lengths of approximately three meters (ten feet) and is required to be threaded on both ends. Additional details on the construction of rigid-steel conduit systems that are used in Saudi Aramco above-grade installations are provided in the section of this Module that is titled "Determining Conduit Installation Requirements."
The requirements for the use of conduit and other equipment (e.g., cables and cable trays) are determined to some extent by the possibility of fire or explosive hazards. The specific classes of hazardous locations are described in the section of this Module that is titled "Determining Hazardous Area Wiring and Sealing Requirements," and they are briefly described here for requirement clarification. A Class I classification describes a location in which flammable gases or vapors could be present. Class II and Class III are locations where combustible dusts or fibers respectively exist. Each of these three classifications are, in turn, broken down further into a Division 1 location in which danger is imminent at any or all times, or a Division 2 location in which danger is not present under normal conditions but is likely to arise. The following are the requirements for the use of rigid-steel conduit in Saudi Aramco above-grade installations:
o Rigid-steel conduit should be used when conduit is to be installed in Class I, Division 1 (hazardous) areas.
o Rigid-steel conduit should be used when exceptional mechanical protection is required.
o Rigid-steel conduit should be used when conduit is installed above ground in outdoor industrial facilities.
o Rigid-steel conduit should be used when conduit is installed in severe corrosive environments; the conduit should be PVC-coated.
o Rigid-steel conduit should be PVC-coated when it is installed in offshore locations or when it is installed within one kilometer (3500 feet) from the shoreline of the Arabian Gulf or thee kilometers (10,500 feet) from the shore line of the Red Sea.
EMT is similar in construction to rigid-steel conduit except that EMT is constructed of a much thinner material. EMT can also be referred to as thin-walled conduit. EMT is manufactured in standard lengths of approximately 3 meters (10 feet). Unlike rigid-steel conduit, EMT is not threaded (due to its thin wall), and it is joined by threadless couplings. Additional details on the construction of EMT systems that are used in Saudi Aramco above-grade installations are provided in the section of this Module that is titled "Determining Conduit Installation Requirements."
EMT does not offer the same degree of mechanical strength as rigid-steel conduit; therefore, the applications of EMT are limited when compared to rigid-steel conduit. The following are the requirements for the use of EMT in Saudi Aramco above-grade installations:
o EMT is acceptable only in non-hazardous (classified), indoor locations.
o EMT should not be used where corrosion can cause damage.
o EMT should not be used where it will be subjected to severe physical damage.
Flexible liquid-tight conduit is constructed of a single strip of aluminum or galvanized steel that is spirally wound and interlocked. An outer jacket is used to make the flexible conduit assembly liquid-tight. The interlocked construction of flexible liquid-tight conduit provides a round cross-section that has a high degree of mechanical strength and great flexibility. Additional details on the use of systems that include flexible liquid-tight conduit in Saudi Aramco above-grade installations are provided in the section of this Module that is titled "Determining Conduit Installation Requirements."
The following are the requirements for the use of flexible liquid-tight conduit in Saudi Aramco above-grade installations:
o Flexible liquid-tight conduit should be used in all areas (except those areas that are classified as Class I, Division 1) for connections where vibration, movement, or adjustments will occur.
o Explosion-proof flexible couplings should be used instead of flexible liquid-tight conduit in Class I, Division 1 (hazardous) locations. When explosion-proof flexible fittings are
necessary, a Crouse-Hinds, EC Series, or equivalent flexible conduit should be used.
Cable Trays: Design, Construction, and Usage Requirements
Cable tray is defined as a unit or an assembly of units or sections (and associated fittings) that is made of metal or some other noncombustible material and that forms a continuous rigid structure. Cable trays are used to support cables and raceways, and they can be found in the form of ladders, troughs, and channels. Although Saudi Aramco standards specify the use of only copper-free, aluminum, ladder-type cable tray for Saudi Aramco above-grade installations, fiberglass, ladder-type cable tray is authorized for use in special applications with the approval of the Proponent Operating Department Manager. This section describes the design and construction of both aluminum and
Aluminum ladder-type cable tray is a prefabricated metal structure that consists of two longitudinal side rails that are connected by individual transverse members at regularly spaced distances. Only ladder-type cable tray is authorized for Saudi Aramco above-grade installations. Because the aluminum cable trays could potentially become energized, they are grounded. To facilitate the transmission of fault current, and because cable trays are hung or mounted in specific lengths, the cable tray lengths must be bonded together. Bonding is the method of joining together the cable tray lengths to ensure electrical continuity.
Ventilated, louvered, cable tray protective covers are required to allow for mechanical protection and solar radiation deflection for all outside cable tray installations. Cable tray covers should be made of the same material that is used for the cable tray, and they should not have a black or dark surface that is exposed to the sun. Covers for aluminum cable tray should be fastened to the cable tray with stainless steel banding. The maximum distance between the stainless steel bands is one band for every 1.5 m (5 feet) of cover length. There should always be at least two bands per length of cable tray. Additional details on the construction of aluminum ladder-type cable tray systems that are used in Saudi Aramco above-grade installations are provided in the section of this Module that is titled "Determining Cable Tray Installation Requirements."
The following are the requirements for the use of aluminum ladder-type cable tray in Saudi Aramco above-grade installations: o Cable tray is the preferred method of power distribution in
Class I, Division 2 (hazardous) areas.
o Cable tray should not be used where it will be subjected to severe physical damage.
o If an outdoor cable tray installation contains only I&C cables, the cable tray covers that are used can be of the solid (unventilated) type.
Fiberglass ladder-type cable tray is an assembly of fiberglass-reinforced plastic tray sections and accessories that form a rigid structural system to support cable. The fiberglass ladder-type cable tray is a prefabricated, sunlight (UV)-resistant, fiberglass structure that consists of two longitudinal side rails that are connected by individual transverse members at regularly spaced distances. Only ladder-type cable trays are authorized for Saudi Aramco above-grade installations. Outdoor, fiberglass cable tray installations should use covers that are made of the same material as the cable tray and that have provisions for ventilation. Additional details on the construction of fiberglass, ladder-type cable tray systems are provided later in this Module.
The following are the requirements for the use of fiberglass ladder-type cable tray in Saudi Aramco above-grade installations:
o Cable tray is the preferred method of power distribution in Class I, Division 2 (hazardous) areas and in unclassified areas.
o Cable tray should not be used where it will be subjected to severe physical damage.
o If an outdoor cable tray installation contains only instrument and control cables, the cable tray covers that are used can be of the solid (unventilated) type.
Exposed Cable: Uses and Routing Requirements
For some Saudi Aramco cable installations, the routing or design of the cable installation may require the cable to be exposed (i.e., not enclosed in a raceway). When the cable will be exposed, metal-clad (Type MC) or armored (in accordance with IEC 60502) cable will be used. Type MC cable and armored cable are
permitted to be installed exposed only when the cable will not be subject to damage by vehicular traffic or similar hazards. If a cable type other than MC or armored cable is installed, the cable should not be installed so that it is exposed above ground. Cable types other than MC or armored cable should only be installed in cable trays, conduit, or flexible liquid-tight conduit. This section of the Module describes the construction, use, and routing
requirements of metal-clad and armored cable that is used in Saudi Aramco installations.
Type MC cable is a factory assembly of one or more conductors that are individually insulated. The assembly is enclosed in a metallic sheath of interlocking tape or in a smooth, corrugated tube. Type MC cable that is used for Saudi Aramco applications should be supplied with a PVC-jacketed aluminum sheath that meets UL 4 (0 to 2000 V) or UL 1072 (2001 to 35 kV)
According to the NEC, the uses of Type MC cable include the following applications:
o Services, feeders, and branch circuits. o Power, lighting, control, and signal circuits. o Indoors or outdoors.
o Where exposed or concealed.
o Direct buried where identified for such use. o In cable tray.
o In any approved raceway. o As an open run of cable.
o As aerial cable on a messenger.
o In hazardous locations as permitted by NEC (NFPA 70), articles 501 through 504.
Type MC cable is always specified with a PVC jacket, and is therefore suitable for installation in wet locations.
Type AC (Armored Cable) cable that is described in NEC Article 333 is light-duty cable that is seldom used in Saudi Aramco installations. The armored cable that is widely used in Saudi Aramco installations is galvanized steel tape or steel wire-armored cable that is manufactured in accordance with IEC Article 502. The IEC-armored cable is heavy duty, and it is considered to be equivalent to NEC Type MC cable. Suitable armored cable terminators should be used to terminate and ground the armor, and the armor should be mechanically joined (bonded) through the installation so that is forms a continuous electric conductor. The cable armor should be connected to all boxes, fittings, and cabinets to provide effective electrical continuity throughout the installation.
Specific installation routing requirements for Type MC cable are listed below:
o Type MC cable should be supported and secured at
intervals not greater than 1.83 m (6 feet) unless the cable is fished. If Type MC cable is installed as a branch circuit in a dwelling unit, the cable should be secured within 305 mm (12 inches) of every outlet box, junction box, cabinet, or fitting.
o Type MC cable that is installed in a cable tray should comply with the installation requirements for cable tray. Routing requirements for cable tray are discussed in the section of this Module that is titled "Determining Cable Tray Installation Requirements."
o The requirements for Type MC cable that is directly buried are discussed in Module EEX 206.03, Evaluating
Underground Wire, Cable, and Conduit Installations.
Specific installation routing requirements for armored cable per IEC 502 are the same as for Type MC cables.
DETERMINING CABLE TRAY INSTALLATION REQUIREMENTS
Generally, the only type of cable tray that is authorized for use in Saudi Aramco installations is copper-free, aluminum ladder-type. However, with the approval of the Proponent Operating Department Manager, fiberglass ladder-type cable tray can be used in special applications. When a cable tray is chosen by the Electrical Engineer for use in a Saudi Aramco installation, there are many factors that should be taken into consideration in the selection of the type and size of the cable tray. The cable tray that is selected should be able to adequately hold the cable (or group of cables) in the installation for the maximum operating life of the installation. The cable tray should be large enough to account for future system growth, but it should not be too large that the tray purchase becomes economically restrictive. There are also requirements that involve the tray installation support structure, grounding, bonding, and placement. This section of the Module provides information on the following topics that are pertinent to determining cable tray installation requirements:
o Loading o Size/Fill
o Magnetic Heating Effects o Circuit Separation
o Grounding and Bonding Requirements and Methods o Tray Separation
o Tray Routing/Protection Covers o Fittings, Bends, and Drops
Cable trays are classified in accordance with their allowable, mechanical, working-load capacity per unit of span length; span is the term that is used to describe the distance between the cable tray supports. The allowable, mechanical, working-load capacity of aluminum and fiberglass cable tray is determined through division of the destruction load capacity of the cable tray (as determined by testing) by a unitless 1.5 safety factor.
The mechanical loading requirements for aluminum cable tray, as defined in NEMA VE-1, are classified in accordance with several load/span class designations. There are three working load categories and four support span categories for aluminum cable tray systems. The working load categories that are specified for aluminum cable tray are as follows:
o Class A - 74.4 kg/m (50 pounds per linear foot) o Class B - 111.6 kg/m (75 pounds per linear foot) o Class C - 148.8 kg/m (100 pounds per linear foot)
The support span categories that are specified for aluminum cable tray are as follows:
o 2.44 m (8 feet) o 3.66 m (12 feet) o 4.87 m (16 feet) o 6.09 m (20 feet)
The table that is shown in Figure 1 lists the class designations that are used to select aluminum, ladder-type, cable tray systems. The class designation is selected through determination of the amount of working load and the length of the support span.
Load/Span Class Designations
Working Load Support
Span Class Lbs./ft kg/m Feet m Designation 50 74.4 8 2.44 8A 75 111.6 8 2.44 8B 100 148.8 8 2.44 8V 50 74.4 12 3.66 12A 75 111.6 12 3.66 12B 100 148.8 12 3.66 12V 50 74.4 16 4.87 16A 75 111.6 16 4.87 16B 100 148.8 16 4.87 16V 50 74.4 20 6.09 20A 75 111.6 20 6.09 20B 100 148.8 20 6.09 20V
Figure 1: Aluminum Cable Tray Load/Span Class Designation (from NEMA VE-1) The mechanical loading requirements for fiberglass cable tray, as defined in NEMA FG-1, are classified in accordance with three working load class designations that are based on a support span of 6.09 m (20 feet). The working load categories that are specified for fiberglass cable tray are as follows:
o Class A - 74.4 kg/m (50 pounds per linear foot) o Class B - 111.6 kg/m (75 pounds per linear foot) o Class C - 148.8 kg/m (100 pounds per linear foot)
Unlike the load/span class designations that are used for aluminum cable tray, the mechanical loading (working load) requirements for fiberglass cable tray vary as the support span distance varies, as shown in Figure 2. The class of fiberglass cable tray that should be used for a given installation is based on the mechanical load that the cable tray must support and the length of the support span that will be used.
Working Load in Lbs./Linear Foot
In Feet Class A Class B Class C
20 50 75 100 18 61 92 123 16 78 117 156 14 100 150 200 12 139 208 10 200
Figure 2: Fiberglass Cable Tray Load/Span Data (from NEMA FG-1)
The amount of mechanical load that a given cable tray will be required to support is determined by the sum of the weight of the cables that will be installed in the cable tray (in pounds per foot). To account for future circuit growth, a 20 percent correction factor is applied to the combined cable weight. Finally, an equivalent weight is added to the corrected combined cable weight to account for the effect of a 200-pound person standing on the cable tray at the center of the span. Details on the procedure to determine the amount of mechanical load that will be present on a given span of cable tray are provided in Work Aid 1.
Because the strength properties of reinforced plastics are reduced when they are continuously exposed to elevated temperatures, the allowable working load of a fiberglass cable tray should be reduced for Saudi Aramco installations in which the cable tray will be exposed to an average ambient temperature of 50 degrees C. The table in Figure 3 shows the approximate percent of strength that the fiberglass cable tray will possess at various temperatures.
Temperature in Degrees C Temperature in Degrees F Approximate Percent of Strength 24 75 100 38 100 90 52 125 78 66 150 68 79 175 60 93 200 52
Figure 3: Fiberglass Cable Tray Temperature Correction for Allowable Working Load (from NEMA FG-1)
In addition to the mechanical loading requirements that have been previously discussed, a completed cable tray system should be able to withstand a horizontal wind force of 1.4 kPa (30 lbf/ft2), which is approximately equivalent to a wind speed of 140 km/hr, or 87 mph.
To determine the cable tray sizes that should be used for a given installation, the Electrical Engineer must evaluate the cable tray fill requirements. The fill requirements differ depending on whether the installation includes multiple-conductor cables that are rated 2000 V or less, single conductor cables that are rated 2000 V or less, or single- and multiple-conductor Type MV or Type MC cables that are greater than 2000 V.
The fill requirements for multiple-conductor cables that are rated 2000 V or less vary with the type of cable that is used (power, lighting, control, and/or signal type cables) and the size of the cables. The fill requirements for single conductor cables that are rated 2000 V or less vary only with the size of the cables. The fill requirements for single- and multiple-conductor Type MV or Type MC cables that are rated for greater than 2000 V vary only with the diameter of the cables that are installed in the cable tray. To determine the correct cable tray size, the cable dimensions (e.g., diameter or cross-sectional area) are added and the sum is multiplied by a growth correction factor. For Saudi Aramco cable tray installations, the growth correction factor recommended is 20 percent. The 20 percent growth correction factor ensures that the cable tray can be used for an increase in load as a result of future expansions. Work Aid 1 describes the procedure that is used to determine the size of a cable tray based on the fill requirements. Magnetic Heating Effects
Metallic raceways are susceptible to magnetic heating effects, which include hysteresis heating and "induced current" heating. Hysteresis heating is caused by the opposition that ferrous raceways offer to a changing magnetic field. The heating occurs due to energy losses within the raceway as the elementary particles (each containing a magnetic field) that exist within the raceway seek to align themselves to the changing magnetic field. Because only aluminum and fiberglass cable tray is authorized for use in Saudi Aramco installations, and because neither material is ferrous, there will be no hysteresis heating effects. Although magnetic hysteresis will not occur in a nonferrous material, induced currents can exist in the nonferrous material if the material is also an electrical conductor (such as aluminum).
Induced current heating caused by alternating magnetic field that exists around the conductors in aluminum cable trays are not significant enough to be a problem.
There are design requirements that can minimize magnetic heating effects. If the phase conductors, neutral conductor (if any), and equipment grounding conductor are grouped within the same raceway, induced current heating can be minimized. When a single conductor that carries an alternating current passes through metal that has magnetic properties, the following actions can be taken to minimize the magnetic heating effects:
o Slots can be cut in the metal between the individual holes through which the conductors pass.
o All of the conductors can be passed through an insulating wall that is large enough for all of the conductors of the circuit.
Circuit separation requirements are established for safety and to minimize the effects of induced currents in adjacent instrument and control cables. Based on the voltages of the cables and the type of cable that is installed in the cable tray (e.g., power, lighting, control, and/or signal-type cables), the circuit separation requirements affect cable routing. When the cable tray systems that contain cables from different systems converge or use the same route, the circuit separation and cable placement requirements that must be observed are described below:
Cables for light and power systems that are rated 600 V or less are permitted to occupy the same cable tray as long as all of the conductors are insulated for the maximum voltage that will exist for any of the cables that are within the cable tray. Cables for light and power systems that are rated above 600 V are not permitted to occupy the same cable tray as cables that are rated 600 V and below unless one of the following conditions is satisfied:
o The cables that are rated above 600 V must be separated from the cables that are rated 600 V or below by a solid, noncombustible, fixed barrier.
Conductors that are used for signaling, instrumentation, or communication systems should not occupy the same cable tray as the conductors of lighting, power, 120 V control, or 24 V dc and above relay control systems.
If all of the cables are insulated for 600 V or more, power systems control, metering, alarm, and relaying circuits that are associated with one major piece of electrical equipment (such as a motor or a transformer) can be run within a single cable tray. Inter-tripping circuits that run between substations can also be run within one cable tray with the following exceptions:
o Circuits that are associated with alternate power sources for primary selective, secondary selective, or spot network substations should be kept separate.
o Differential relay circuits should be kept separate from all other circuits.
Circuit separation and placement requirements for instrument cables in Saudi Aramco installations are shown in Figure 4. To determine the minimum circuit separation distance that should be maintained between two systems, the first system in the first column and the second system in the first row should be located; the intersection of the two systems in the table is the minimum circuit separation distance. For example, the minimum circuit separation distance that should exist between 125 V dc systems and RTD systems in cable tray is 6 inches (150 mm).
If the insulation of the cables that are installed in the raceway is rated for at least 450 to 750 V, there are no minimum circuit separation requirements between power and/or control conductors for dc or for ac circuits that carry power at voltages that are less than 1000 V.
RTD Thermo-couple Milli- Volt Pulse 4-20 mA Analog (24 VDC) 24 VDC 48 VDC 125 VDC 120 VAC >120 VAC RTD 0 0 0 0 1 (25) 6 (150) 12 (300) 24 (600) Thermo Couple 0 0 0 0 1 (25) 6 (150) 12 (300) 24 (600) Milli-Volt Pulse 0 0 0 0 1 (25) 6 (150) 12 (300) 24 (600) 4-20 mA Analog (24 VDC) 0 0 0 0 1 (25) 6 (150) 12 (300) 24 (600) 24 VDC 48 VDC 1 (25) 1 (25) 1 (25) 1 (25) 0 6 (150) 6 (150) 18 (450) 125 VDC 6 (150) 6 (150) 6 (150) 6 (150) 6 (150) 0 0 12 (300) 120 VAC 12 (300) 12 (300) 12 (300) 12 (300) 6 (150) 0 0 12 (300) >120 VAC 24 (600) 24 (600) 24 (600) 24 (600) 18 (450) 12 (300) 12 (300) 0
Note that all values are shown in inches (millimeters)
Figure 4: Minimum Circuit Separation Distances for Signal Cabling in Cable Tray (from SAES-J-902)
Cables that carry different signal types should also be routed so that they cross each other only at right angles. Also, when dc instrumentation and control signal cabling is routed past a source of strong electromagnetic fields (such as transformers, motors, and generators that are rated greater than 100 kVA), a minimum spacing of 2 m (6 feet) should be maintained between the signal cabling and the source of the electromagnetic field. When trays that contain different systems converge or use the same route, they should preferably be placed in the following order (from top to bottom in different trays as required):
o Power cables. o Control cables.
o Alarm circuits.
o Dc electronic cables and pneumatic tubing (the pneumatic tubing should be separated from the dc circuit by a barrier). o Thermocouple cables.
Grounding and Bonding Requirements and Methods
In most high-voltage power distribution cables, there are various metallic support systems (e.g., shields and cable trays) that could carry fault or induced currents. Equipment grounding describes the manner of grounding the support system equipment. Bonding describes the manner of electrically interconnecting the various segments of the support systems. An equipment grounding conductor is not the same as a grounded conductor in that a grounding conductor carries only current during fault conditions while the grounded conductor may carry current under normal conditions. Cable trays must be grounded and bonded so that freedom from dangerous electric shock voltages is ensured and that sufficient current-carrying capability is provided to accept the ground-fault current that is required by the overcurrent protection system.
For Saudi Aramco installations, the entire cable tray system is required to be mechanically and electrically connected to ensure that there is a path for electric fault current. The acceptable methods that are used to meet the grounding requirements for aluminum cable trays are listed as follows:
o Enclosures of MCCs, motor controllers, switchgear, and other electrical devices that are fed from a cable tray system should be structurally and mechanically connected and bonded to the cable tray system.
o With some exceptions, a conduit, cable tray, cable armor, or cable shield should not be used as the sole means of
grounding equipment. For safety and reliability, a grounding conductor should be installed in the same cable tray as the power conductors.
o A metallic cable tray should be grounded at both of its end points.
The acceptable methods that are used to meet the bonding requirements for aluminum cable trays are listed as follows:
o To prevent any faults that may occur within the cable tray system from arcing to ground, metallic cable trays should be bonded to the plant grounding system at maximum intervals of 25 m (84 feet).
o Bonding can be accomplished through use of metallic connections to the building or structural columns that support the cable trays.
o Bonding jumpers should be provided whenever a cable tray is insulated from its metallic supporting structure or
whenever a cable tray expansion joint is used. Expansion fittings (or joints) are required to accommodate expansion and contraction due to ambient temperature changes. The gap at expansion points depends on the spacing between these joints.
NEC Article 318 requires sufficient space around cable trays to permit adequate access for installation and maintaining the cables. Saudi Aramco standards no longer specify distances (tray separation). The following separation distances were specified before 1984 and can be used as guidelines if possible.
For separation between multiple horizontal cable tray systems, a minimum of 50 mm (2 inches) of separation should be provided between the cable tray side rails. A minimum of 25 mm (1 inch) of separation should be provided between any vertical support and a cable tray side rail.
No more than four 750 mm (30 inch) cable trays or four 600 mm (24 inch) cable trays should be located adjacent to each other on one horizontal tier. If more than four cable trays are required, a 450 mm (18 inch) spacing should be provided between each group of four cable tray units so that access is provided to each of the cable tray groups.
The separation between vertical-tiered cable trays should be at least 450 mm (18 inches) with a minimum clear space of 300 mm (12 inches); if the total combined width of a given cable tray tier exceeds 900 mm (36 inches), the vertical space should be increased by 150 mm (6 inches). If the total width of the cable tray system exceeds 900 mm (36 inches), the vertical clearance should be increased to 450 mm (18 inches).
The lower voltage cables are usually placed in the bottom cable trays, and the higher voltage cables in the upper cable trays. The vertical space between a cable tray and a ceiling, beam, or other obstruction should be a minimum of 300 mm (12 inches). When cable tray is located over any electrical gear, 600 to 900 mm (24 to 36 inches) of vertical separation should be maintained from the top of the electrical gear to the bottom of the cable tray. Supports/Fastenings
To ensure adequate support, cable tray supports should be constructed from hot-dip galvanized steel. Cable tray supports that are installed in severe corrosive environments should be protected through use of one of the following methods:
o PVC-coated at the factory.
o Coated in the field prior to installation.
The following were requirements of the standards prior to 1984 and can be used as guidelines if possible.
Indoor ceiling hangars that are used for cable tray supports should be made from 12 mm (1/2 inch) galvanized-steel rods. All supports that are used for cable trays should provide a minimum weight-bearing surface of 45 mm (1 and 3/4 inches) as well as provisions for hold-down clamps and fasteners. The hold-down clamps and fasteners should be used at all cable tray support points. Vertical cable tray fasteners should not rely on friction to secure the cable tray to its supports.
Cable trays should be supported from the structural steel of pipeways and buildings with noncombustible racks or hangers. Cable tray supports should to be spaced a maximum of 6 m (20 feet) on horizontal runs or 2.4 m (8 feet) on vertical runs. When ceiling hangers are used to support the cable tray, the hangers should be spaced no more than 3 m (10 feet) apart. Cantilever cable tray sections should be limited to a length of 900 mm (3 feet); additional support should be provided for cantilever cable tray sections that are greater than 900 mm in length.
Cable tray splice points should not be located directly over the cable tray supports, and they should not be located at mid-span. The ideal location for a cable tray splice point is within the one quarter points of the span as measured from the cable tray supports. For example, if there are 4 meters between cable supports, the splice point should be within 1 meter of either cable support. Splice plates, expansion joints, and connectors should join the cable tray sections so that the rated vertical and horizontal load of the cable tray is not diminished.
All cables should be fastened to the cable tray every 1.8 m (6 feet) on horizontal cable tray runs, every 450 mm (18 inches) on vertical cable tray runs, and every 450 mm (18 inches) on cable tray bends (horizontal and vertical). Vertical cable tray systems should provide suitable methods of cable support through the use of cable hangers or metal clamps. Nylon cable ties can be used for most fastening applications. Cable ties in outdoor locations should be black, and they should also be resistant to UV radiation. When circuits in cable trays are paralleled, single conductor cables should be fastened in groups that include one conductor per phase or neutral to prevent current imbalance.
Tray Routing/Protection Covers
The following can be used as guidelines, where possible.
For Saudi Aramco installations, there are certain requirements for cable tray routing and cable tray protective covers. Considerations that are taken into account when routing cable tray systems are utilization of building walls as structural support and the proximity to hazardous equipment, process equipment, and grid-type walkways. Cable tray should be run parallel to the building structure or the building walls as applicable. Also, cable tray should not be routed any closer than 7.5 m (25 feet) horizontally to any fire hazardous equipment or other types of equipment that can produce temperatures that could damage the cables that are installed in the cable tray, such as steam lines. Cable trays should be located above all process piping and other process facilities. When cable trays are routed under grid-type walkways, barriers should be used to add additional protection to the cable tray. When installed, these barriers should not hinder cable tray ventilation. For cable tray locations to which future cable installations will be added, extra space should be provided in the cable tray. The extra space should allow for the future installation of the same basic type of cable tray and should be arranged so that the spare space will be unused and available for the future installation.
The following circumstances would require the use of protective covers on a cable tray system:
o When cable trays pass through walls.
o When cable trays are near areas that could be damaged by workers or by nearby equipment.
o When cable trays are routed outdoors.
When cable trays pass through a combustible partition or wall, the cable tray should be completely enclosed in metal with a bushed steel conduit sleeve or similar device. When cable tray entry occurs in switch and control houses or when the cable tray passes through a fire wall, the cables in the cable tray should be sealed
To allow for drainage, cable trays that enter a building should be sloped away from the building at a minimum rate of ten millimeters per meter of cable tray (1/8 inch per foot). A concrete curb or metal kick plate should be provided for cable tray that passes vertically through floors or platforms. To prevent contact with or damage to the exposed cables, the tray should also be covered on all sides to a distance of 1.8 m (6 feet) above the floor or platform. Although the cable trays will be provided with covers, cables that are installed in outdoor cable trays should have sunlight-resistant (UV radiation-resistant) jackets. Ventilated, louvered cable tray covers are required to provide mechanical protection and solar radiation deflection for all outside cable tray installations. Covers for aluminum cable tray should be fastened to the cable tray with stainless steel banding at a rate of one band per 1.5 m (5 feet) of cover length and at least two bands per length of tray. Cable tray covers should not have a black or dark surface that is exposed to the sun.
Fittings, Bends, and Drops
For Saudi Aramco cable tray installations, the cable trays require the use of specific fittings, elbows, bends, and drops. Recommendations: vertical and horizontal elbows should have a minimum radius of 300 mm (12 inches), but they should not be less than the minimum cable bending radii. For vertical drops that are greater than 1.5 m (5 feet), outside vertical elbows and drop out fittings should be used at the higher elevation. For vertical drops that are greater than 4.5 m (15 feet), inside vertical elbows should be used at the lower elevation. Horizontal elbows should be used for changes of direction that occur at the same elevation.
DETERMINING CONDUIT INSTALLATION REQUIREMENTS
Prior to the installation of an above-grade conduit system, the Electrical Engineer should examine the various factors that will affect the installation. These factors include the type of equipment that is to be installed, the installation method that will be used, and the classification of the area in which the equipment will be installed. The requirements of SAES-P-104 (Wiring Methods and Materials) should be followed for Saudi Aramco above-grade conduit installations.
The conduit installation method that is used (rigid-steel conduit, EMT, or flexible liquid-tight conduit) will affect the routing requirements of the installation. Other determinations, such as the correct size of the conduit for the installation, must also be made with respect to routing the conduit and cabling. The hazardous classification of the installation location determine the sealing and termination requirements. This section of the Module describes the following aspects of determining conduit installation requirements:
o Conduit Types and Applications o Conduit Sizing and Routing o Conduit Bending o Conduit Threading
o Indoor and Outdoor Conduit Termination o Conduit Supports
Conduit Types and Applications
The types of conduit that are available for use by Saudi Aramco in above-grade conduit systems are rigid-steel conduit, EMT, and flexible liquid-tight conduit. IMC is prohibited for use in Saudi Aramco installations. The additional cost of rigid-steel conduit is considered to be worth the added protection that it offers over IMC.
Hot-dipped, galvanized, rigid-steel conduit is specified for all Saudi Aramco installations in which rigid-steel conduit is used. The application requirements of rigid-steel conduit systems have been described previously in this module and are listed briefly as follows:
o Used for Class I, Division 1 areas.
o Used when exceptional mechanical protection is required. o Used when conduit is installed above ground in outdoor
o Used when conduit is installed in severe corrosive environments
o If installed in severe corrosive environments, the rigid-steel conduit should be PVC-coated.
EMT does not offer the same degree of mechanical strength that is offered by rigid-steel conduit, and it should not be used where it is subjected to severe physical damage. EMT is only acceptable in nonhazardous, indoor locations, and it should not be used where corrosion can cause damage.
The applications of flexible liquid-tight conduit are limited to connections in which vibration, movement, or adjustments will occur. Flexible liquid-tight conduit is allowed for use in all areas except Class I, Division 1 hazardous locations.
Conduit Sizing and Routing
Two critical aspects of a conduit installation are conduit sizing and conduit routing. When the conduit size is chosen, the conduit inside diameter should be large enough to install all of the cables that were selected to be installed in that conduit without damage to any of the cables. The conduit should also be large enough to minimize any adverse heating effects on the conduit or on the cables that are contained within the conduit. When the conduit is installed, there are also routing and placement requirements that should be met. The routing requirements are important to minimize inter-conduit heating and conduit heating that results when a conduit is routed near process facility equipment that radiates heat.
Conduit fill is expressed as a percentage of the cross-sectional area of the conduit that the cables are allowed to occupy, and it depends on the number of conductors that are to be installed in the conduit. The allowable percentage of conduit fill is based on the combined heating effects of all of the cables that are installed in the conduit. Knowledge of the allowable percentage of conduit fill helps the Electrical Engineer to select the proper size of conduit for a particular installation.
The table in Figure 5 describes the various size requirements that are specified for rigid-steel conduit, EMT, and flexible liquid-tight conduit; the references for each requirement are also listed. The size requirements include the minimum size of the conduit, the maximum size of the conduit, and the allowable conduit fill.
Conduit Sizing Requirements
Rigid-Steel Conduit EMT Flexible Liquid
Tight Conduit Minimum Size ¾” except instrument
panels, inside buildings, prefabriacted skids, or non-industrial areas Size requirements are the same as those specified for rigid-steel conduit. Size requirements are the same as those specified for rigid-steel conduit.
Maximum Size N/A 4” 4”
Allowable Conduit Fill
Refer to Figure 6 Allowable conduit fill
requirements are the same as those for rigid-steel conduit.
All conduit fill requirements are the same as those specified for rigid-steel conduit. Figure 5: Conduit Sizing Requirements
To determine the allowable fill, the Electrical Engineer should first choose an applicable duct from the tables for selecting conduit size that are shown in Work Aid 2. Once the size of the conduit is selected, the total cross sectional area of all of the cables that will be contained in the conduit should be determined through use of the table of cable dimensions that is shown in Work Aid 2. Now that the cross-sectional area of the cables has been determined and the conduit has been chosen, the percentage fill of the conduit can be determined. Work Aid 2 provides the tables and the details on the procedure that is used to size conduit for Saudi Aramco, above-grade installations. The allowable percentage of conduit fill, based on the number of conductors that are to be installed in the
When conduit sealing fittings are used (type EYS or similar), the wire fill of the conduit sealing must not exceed 25% based on the conduit size (i.e., the ratio of the sum of the cross-sectional areas of wires and multi-conductor cables to the internal cross-sectional area of a conduit of the same trade size must not exceed 25%). If the percentage of fill of the conduit sealing exceeds 25%, oversized sealing fittings with reducers may be used in order to use the highest permissible conduit wire fill.
Percent of Cross Section of Conduit and Tubing for Conductors
Number of Conductors 1 2 Over 2
All conductor types 5
31 40 Note. A multi-conductor cable of two or more conductors shall be treated as a single conductor cable for calculating percentage conduit fill area. For cables that have elliptical cross section, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.
Figure 6: Allowable Percentage of Conduit Fill (from NEC, Chapter 9)
The natural weight of the cables that are contained in the conduit will cause them to settle to the lowest part of the conduit that the conduit space will allow. Depending on the size, configuration, and number of cables, the cables could get jammed in the conduit during installation. A useful unitless value that is used when cables are installed in conduit is called the "jam ratio." The jam ratio is used primarily during cable pulling tension calculations, and it will be explained in detail in that section of this Module; but it is also used in the conduit selection process, and, so, it will be described briefly here. The jam ratio is the ratio of the conduit's inside diameter to the diameter of the largest cable that will be installed in the conduit. The jam ratio provides a factor that describes the probability that the cable will jam during its installation in the conduit. The equation below is used to calculate the jam ratio:
D 1.05 = Ratio Jam
"D" is the conduit inside diameter.
"d" is the diameter of the largest cable that is in the conduit. "1.05" includes a correction factor of 5% that accounts for the
oval cross-section of conduit bends.
Cable Clearance Within the Conduit
If the jam ratio is greater than 3.0, jamming is not likely to occur, and cable clearance can be ignored. If the jam ratio is between 2.5 and 2.8, jamming is probable; if the jam ratio is between 2.8 and 3.0, serious jamming is probable. If jamming is probable, the Electrical Engineer should evaluate the need to increase the size of the conduit.
Cable clearance is the distance between the uppermost cable in a conduit and the inside top of the conduit. A gap should be present between the uppermost cable in a conduit and the top of the conduit to prevent rubbing during pulls and to allow for expansion and contraction.
For a single cable installation, the cable clearance is calculated through use of the following equation:
Clearance = D - d where:
"D" is the conduit inside diameter.
"d" is the diameter of the largest cable that is in the conduit. For a three cable installation (or three tripled conductors), the cable clearance is calculated using the following equation:
⋅ d D-d -1 2 d) -(D + 1.366(d) -2 D = Clearance 2
The cable clearance should be maintained within a band of 6 to 25 mm (1/4 to 1 inch). If the cable clearance is less than 6 mm (1/4 inch), the cable clearance is not satisfactory, and the Electrical Engineer should evaluate the need to increase the size of the conduit.
Magnetic Heating Effects
Metallic raceways are susceptible to magnetic heating effects, which include induced current heating and hysteresis heating. In order to avoid magnetic heating effects, all phase and neutral conductors of a three phase system must be in one conduit, or if there are parallel conductors, each conduit must have all phases and neutral.
The conduit clearance is defined as the distance between the outside surface of a conduit and walls, other conduit, or other equipment. When routing conduit for above-grade installations, proper conduit clearances should be established. The conduit clearance is required to ensure that the conduit is not routed too close to process facility equipment that radiates heat.
Conduit runs should be symmetrical and should be routed vertically, horizontally, or parallel to structure lines. Conduit should not be installed near ladder rungs or at platform levels so that the conduit restricts passage or interferes with existing steps.
As a guideline, the minimum clearance for conduits that cross or run parallel to process lines should be 150 mm (6 inches) for uninsulated process lines and 100 mm (4 inches) for insulated process lines.
Fireproofing is required for critical power and control cables that are located above ground in a fire-hazardous zone, e.g., within 7.5 m (25 feet) horizontally of fire-hazardous equipment. Critical power and control cables are cables whose loss would render emergency shutdown, fire protection, or alarm systems inoperative. Fire-hazardous equipment is defined as equipment
Fireproofing must provide a minimum of 15 minutes of protection to the integrity of the circuit against temperatures of 1100°C (2000°F) in accordance with UL 1709.
Conduit bending requirements for a given installation are designed so that the conduit is not injured during the installation and so that the internal diameter of the bent conduit is not effectively reduced. No more than four quarter conduit bends (360 degrees total) should be made in one run of conduit between pull points. Minimum conduit bending radii requirements are based on the minimum cable training radii for the cable that is to be installed in the conduit and the physical size of the conduit.
Minimum Bending Radii
If a wire or cable is bent too much, the act of bending may cause damage to the wire or cable that results in subsequent cable failure. To prevent cable failure, a minimum bending radius (curvature of bend) limits cable and wire bending. With large power distribution cables, the construction of the cables (e.g., insulation and shielding) places additional restrictions on the minimum bending radius that a cable can withstand before damage to the cable will occur. As a cable passes, enters, or exits a conduit, the cable will usually have to be bent. The act of bending a wire or cable during the installation process is called "training." The minimum bending radius of any cable should not be exceeded when the cable is trained in a conduit.
To prevent damage to the cables during the installation process, the minimum bending radii of the cables must also be considered during cable installation. The minimum bending radii of the inner surface of a given cable is determined through use of a calculation in which a specific multiplication factor is multiplied by the overall diameter of the cable.
Before the minimum bending radii of the conduit is specified, the minimum cable training radii of the cables should be determined. To ensure that damage will not occur to the cables when they are trained, the minimum conduit bending radii should not be less than the minimum cable training radii. The procedure that is used to determine the cable minimum bending radii is provided in Work Aid 2.
The minimum conduit bending radii is selected from a table based on the size of the conduit that is used for the installation. A hand bender can be used to make field bends for conduit that is sized at 1-1/2 inches or less. A bending machine should be used for conduit that is larger than 1-1/2 inches. Bends that are accomplished with a hand bender are measured from the inner surface of the conduit; bends that are accomplished with a machine bender are measured from the center line of the conduit. Work Aid 2 provides the procedure that is used to determine conduit bending requirements for Saudi Aramco above-grade installations.
Rigid-steel conduit is required to be threaded on both ends for Saudi Aramco conduit installations. Because EMT has a thin wall, individual sections of EMT are only permitted to be joined through use of threadless couplings.
Rigid-steel conduit is manufactured in standard lengths of 10 feet (3 m). During an installation, the conduit must be cut into proper lengths. The proper length to which the rigid-steel is cut is dependent on the location and conditions of the conduit installation. After the conduit has been cut to the proper length, it must be field-threaded and then chamfered (reamed) to remove the burrs and sharp edges that are formed during cutting. All field threads for rigid-steel conduit are required to be full and continuous. A minimum thread engagement of five full threads should be made at all fittings. Field threads should be cut with a standard conduit cutting die that has a 3/4 inch taper per foot. All conduit threads must be tapered; running threads are not permitted for any application. Raw threads should be protected from corrosion with CRC "Zinc-It" or an equivalent coating.
Rigid-metal conduit is available in sizes of 1/2 to 6 inches. Conduit trade sizes are referred to as the approximate inside diameter of the raceway. All fittings and knockouts on boxes are identified by the trade size of the raceway for which the device is intended. Figure 7 describes the required dimensions of conduit threads for the various trade sizes of rigid-steel conduit. Critical measurements include the effective length of the threads (L2), the
total length of the threads (L4), the pitch diameter at the end of the
conduit (E0), and the required number of threads per inch of
conduit. L4 total length of threadsa L2 effective length of threads E0 pitch diameter at end of conduit Trade size of conduit in inches Number of threads per inch
inches mm inches mm inchesb mmb
3/8 18 0.60 15.2 0.41 10.4 0.612 15.5 ½ 14 0.78 19.8 0.53 13.5 0.758 19.3 ¾ 14 0.79 20.1 0.55 14.0 0.968 24.6 1 11 ½ 0.98 24.9 0.68 17.3 1.214 30.8 1 ¼ 11 ½ 1.01 25.7 0.71 18.0 1.557 39.5 1 ½ 11 ½ 1.03 26.2 0.72 18.3 1.796 45.6 2 11 ½ 1.06 26.9 0.76 19.3 2.269 57.6 2 ½ 8 1.57 39.9 1.14 29.0 2.720 69.1 3 8 1.63 41.4 1.20 30.5 3.341 84.9 3 ½ 8 1.68 42.7 1.25 31.8 3.838 97.5 4 8 1.73 43.9 1.30 33.0 4.334 110.1 5 8 1.84 46.7 1.41 35.8 5.391 136.9 6 8 1.95 49.5 1.51 38.4 6.446 163.7
a A minus tolerance of one thread applies to the total length of threads L 4 b Plus and minus tolerances of one turn apply to the pitch diameter E
Indoor and Outdoor Conduit Terminations
Metal raceways should be mechanically joined to form a continuous electric conductor; raceways should also be connected to all boxes, fittings, and cabinets for effective electrical continuity. Conduit terminations are used to complete the conduit system through connection of the metal raceway (i.e., rigid-steel conduit or EMT) to the boxes, fittings, and/or cabinets that are used in the conduit system.
Conduit systems can terminate at service entrance fittings, panels, pull boxes, or access fittings, and they can include the use of insulated bushings and conduit seals. For example, indoor conduit runs that terminate in the open should be equipped with an insulating bushing. Outdoor conduit that terminates in the open should be equipped with a service entrance fitting. Also, insulating grounding bushings should be installed on conduit that is inside of all boxes except where a threaded hub is provided as part of the conduit thread connection.
A fitting is an accessory that is provided for a conduit system. Fittings are used to perform mechanical connections to conduit and associated conduit support equipment. Items, such as lock nuts, bushings, conduit couplings, EMT connectors and couplings, and threadless connectors, are considered to be fittings. Conduit fittings should be made of cast or forged steel, cast iron, or malleable iron that is either hot-dip galvanized or zinc electroplated (as supplied by the manufacturer). Aluminum fittings are not allowed for use in Saudi Aramco conduit installations. Only malleable iron sealing fittings are to be used for new installations, However, for repair purposes, gray, cast iron, split-type retro-fit sealing fittings are allowed.
For the connection of conduit, EMT, or other raceways (except cable trays), a box or fitting should be installed at each conductor splice connection point, outlet, switch, junction point, or pull point. Conduit bodies are considered to be fittings and are allowed to contain splices if they have adequate volume.
All conduit fittings should be accessible from a platform, ladder, or stairwell. Cover openings should not be blocked by any structural steel or pipe that would prevent access to the interior of the fitting for maintenance.
For indoor and outdoor conduit terminations, there are certain requirements that should be met. Indoor conduit runs that terminate in the open should be equipped with an insulating bushing. Outdoor conduit that terminates in the open should be equipped with a service entrance fitting. Insulated grounding bushings should be installed on conduits inside of all boxes except where a threaded hub is provided as part of the conduit thread connection.
Seals (Explosion Proof)
Explosion proof seals in a conduit system should only be provided where required by the NEC. Non-required sealing is expensive and an operational problem since for any future circuit modifications the seal fitting must be cut out and, the conductors spliced or removed. In additon, each conduit entering a process unit control house should be sealed outside the point of entry for above grade runs and inside at the point of entry for below grade runs.
Seals, when required, should be located within 450 mm (18 in.) of an enclosure.
Vertical or horizontal conduit runs which require sealing should be sealed with combination vertical/horizontal seals, EYS or equal. Explosion proof seals should be filled as follows:
(a) A dam of fiber (Chico “X” or equal) should be made around and between the wires to prevent the sealing compound from entering a conduit run.
(b) After fixing the dam, the sealing compound (Chico “A” or equal) equal to the diameter of the conduit (but not less than 5/8 inch) should be poured into the seal.
(c) All sealing compound should be mixed with clean fresh water.
Wire fill of sealing fittings should not exceed 25% based on the size of the conduit.
An expansion joint is a mechanical device that is used to allow for the thermal expansion and contraction of a run of conduit. Because a given run of conduit that is placed in an above-grade conduit installation will be exposed to considerable temperature fluctuations over a year, expansion joints should be considered. However, expansion joints should not be used for long, vertical conduit runs; the conduit should be offset whenever possible to allow for the expansion and contraction of the conduit.
An expansion joint should be installed in any run of conduit that is over 60 m (197 feet) in length. Additional expansion joints are required at intervals of 120 m (394 feet) unless the conduit run is supported by a steel structure such as a pipeway. When only one expansion joint is used for a run of conduit, the expansion joint should be located at the midpoint of the straight run. Multiple expansion joints should be equally spaced in the straight run. When a run of conduit is supported by a steel structure, the conduit expansion joints should be provided at the same location as the expansion joints that are provided for that steel structure. Conduit Supports
A conduit support is a mechanical device that provides structural strength for a vertical or horizontal conduit system. Conduit supports should be constructed of cast or forged steel, cast iron, or malleable iron, and they should be either hot-dip galvanized or zinc electroplated as supplied by the manufacturer.
Conduit supports can be used for single conduit runs or for grouped conduit runs. For single conduit runs on bare steel, U-bolts or one-hole malleable clamps (bolted to steel) should be used. U-bolts should also be used for the conduit support whenever the structure to which the conduit is mounted is subject to vibration. Single conduit runs on concrete or masonry should be supported with one-hole malleable clamps with expansion bolts. If the conduit run is on hollow tile, one-hole malleable clamps with toggle bolts should be used. Grouped conduit runs should be supported with suitable field fabricated hangars or Unistrut-type supports (or equivalent).
Except when expansion joints are included in a straight run of conduit, the clamps and straps that are used for conduit supports should be made specifically for the trade size of the conduit. When expansion joints are used, one normal size conduit clamp should be firmly attached at each midpoint between adjacent expansion joints. Also, one normal size conduit clamp should be firmly attached at the midpoints that exist between both ends of the conduit run and the adjacent expansion joints. The clamp is used to equalize the expansion and contraction that occur at each expansion joint. All other conduit supports that are used when an expansion joint is present should be oversized conduit clamps that allow the conduit to move axially (along the axis). Clamps that rely on friction for their support on the base structure (such as Korns clamps) should not be used for the oversized clamps. In straight conduit runs that include an expansion joint, U-bolt-type clamps that are securely bolted to the base structure are acceptable for use.
Conduit runs should not be supported from process lines or other pipelines unless no other practical method is available. The minimum clearance for conduit that crosses or runs parallel to process lines is 150 mm (6 inches) for uninsulated process lines and 100 mm (4 inches) for insulated process lines.
The maximum distance that is allowed between rigid-metal conduit supports is dependent on the size of the conduit. The table in Figure 8 contains the maximum distance both in meters (m) and in feet (ft) for various conduit sizes.
To ensure that the conduit system remains rigid and vibration-free, additional conduit supports may be required at bends, fittings, and fixtures. Conduit supports should be located at a maximum of 1 m (3 feet) from each outlet box, junction box, or fitting. In order to allow the conduit to flex when a long horizontal run of conduit ends in an angle or a bend, the next clamp around the angle or bend should not be placed adjacent to the angle or bend.
Conduit Size (in.) M ft.
½ and ¾ 3 10
1 3.6 12
1 ¼ and 1 ½ 4.2 14
2 and 2 ½ 4.8 16
3 and larger 6.0 20
DETERMINING CABLE PULLING REQUIREMENTS
To install a cable into a conduit, it must be pulled from one end of the conduit to the other with a strong wire. When a cable is pulled into a conduit, there are maximum pulling tensions that the cable can withstand without damage. There are various types of pulling equipment that can be used to pull a cable into a conduit. Each different type of pulling equipment has a maximum pulling tension (or pulling force) that it can withstand. The configuration of the conduit, the type of cable that is to be installed, and the types of pulling equipment that are chosen for the installation should all be evaluated so that damage to the cable or to any installation equipment does not occur. Calculations to determine the maximum pulling tensions that could occur with various conduit configuration and pulling equipment combinations are performed during the design phase of an installation. These calculations are evaluated to ensure that maximum pulling tensions are not exceeded during a cable installation pull.
There are various ways to reduce the pulling tension for a given cable installation: the rigging equipment can be varied, the size of the conduit can be increased, the conduit configuration (e.g., turns or angles) can be altered, or the pull point frequency can be changed. This section of the Module provides information on the following topics that are pertinent to determining cable pulling requirements:
o Rigging Procedures o Cable Pulling Parameters Rigging Procedures
During the design phase of the wire or cable installation, once the installation type (e.g., conduit) and the cable route have been chosen, the Electrical Engineer selects a rigging method and then performs a pulling tension calculation. If the pulling tension calculation indicates that maximum tensions could be exceeded by the cable pull, design changes are made. Before the cable pulling parameters and pulling tension calculations are described, a description of the cable rigging equipment and methods is necessary.