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. Cable and Raceway Requirements All building wiring must be enclosed in a cable, conduit, wire way, or raceway. During installation, conductors are snaked through conduit or tubing, are laid in a wireway, or are contained in cables and secured to structural framing. Care must be exercised in placing conductors, as conductors and insulation can be easily damaged. For example, if a conductor is pulled through a tight conduit, it can stretch. Deformation caused by stretching reduces the cross-sectional area of the wire, thereby reducing its ampacity. This creates an unsafe condition because the conductor can overheat. Tbl.7 indicates the recommended maximum number of conductors allowed in conduit or tubing for conductors with THWN or THHN insulation. Similar tables exist in the electrical code for this and other insulation types. These recommended values are less than those typically established as maximum values in the electrical code. They are recommended maximums because they allow for less cumbersome installation (e.g., pulling conductors through conduit) and are based on industry experience. They allow for future expansion (adding conductors). Ex. **8 Recommend the maximum number of No. 12 AWG THWN conductors that should be placed in a 3/4 EMT conduit, based on information in Tbl.7. From Tbl.7, 8 conductors maximum. Ex. **9 Recommend the minimum EMT conduit size for three No. 4 AWG THWN current-carrying conductors, based on information in Tbl.7. From Tbl.7, a 1 1/4 in conduit is recommended. === Tbl. **6 A SYSTEM FOR COLOR CODING AND IDENTIFICATION MARKINGS FOR CONDUCTORS. Voltage System Color and Identification Marking Code [120 V AC single phase, two wire 120/240 V AC single phase, three wire 208Y/120 V AC three phase, four wire 480Y/277 V AC three phase, four wire 240 ?/120 V AC three phase, three wire 480 ? V AC three phase, three wire] [• Grounded neutral, white (first or only neutral in raceway, box, auxiliary gutter, or other types of enclosures) • Grounded neutral, white with black stripe running entire length of insulation (when neutral is installed in raceway, box, auxiliary gutter, or other types of enclosures with another neutral) • Grounding conductor, green, green with one or more yellow stripes, green tape, or bare • Ungrounded conductor, black with "120V-1PH" marking • Grounded neutral, white (first or only neutral in raceway, box, auxiliary gutter, or other types of enclosures) • Grounded neutral, white with brown stripe running entire length of insulation (when neutral is installed in raceway, box, auxiliary gutter, or other types of enclosures with another neutral) • Grounding conductor, green, green with one or more yellow stripes, green tape, or bare • Ungrounded conductor, black with "240/120V-1PH-A" marking • Ungrounded conductor, red with "240/120V-1PH-B" marking • Grounded neutral, white (first or only neutral in raceway, box, auxiliary gutter, or other types of enclosures) • Grounded neutral, white with red stripe running entire length of insulation (when neutral is installed in raceway, box, auxiliary gutter, or other types of enclosures with another neutral) • Grounding conductor, green, green with one or more yellow stripes, green tape, or bare • Phase X (ungrounded) conductor, black with "208Y/120V-3PH-X" marking • Phase Y (ungrounded) conductor, red with "208Y/120V-3PH-Y" marking • Phase Z (ungrounded) conductor, blue with "208Y/120V-3PH-Z" marking • Grounded neutral, white (first or only neutral in raceway, box, auxiliary gutter, or other types of enclosures) • Grounded neutral, white with yellow stripe running entire length of insulation (when neutral is installed in raceway, box, auxiliary gutter, or other types of enclosures with another neutral) • Grounding conductor, green, green with one or more yellow stripes, green tape, or bare • Phase X (ungrounded) conductor, brown with "480Y/277V-3PH-X" marking • Phase Y (ungrounded) conductor, orange with "480Y/277V-3PH-Y" marking • Phase Z (ungrounded) conductor, yellow with "480Y/277V-3PH-Z" marking • Grounding conductor, green, green with one or more yellow stripes, green tape, or bare • Phase X (ungrounded) conductor, black with "240VD-3PH-X" marking • Phase Y (ungrounded) conductor, black with "240VD-3PH-Y" marking • Phase Z (ungrounded) conductor, black with "240VD-3PH-Z" marking • Grounding conductor, green, green with one or more yellow stripes, green tape, or bare • Phase X (ungrounded) conductor, brown with "480VD-3PH-X" marking • Phase Y (ungrounded) conductor, orange with "480VD-3PH-Y" marking • Phase Z (ungrounded) conductor, yellow with "480VD-3PH-Z" marking] === Tbl. **7 RECOMMENDED MAXIMUM NUMBER OF CONDUCTORS IN METAL (EMT) AND PLASTIC (PVC) CONDUIT FOR CONDUCTORS WITH THWN, THHN, AND THW-2 INSULATION. VALUES SUGGESTED IN THIS Tbl. ARE LESS THAN THOSE TYPICALLY ESTABLISHED AS MAXIMUM VALUES IN THE ELECTRICAL CODE. THE RECOMMENDED MAXIMUM VALUES PROVIDED ALLOW FOR LESS CUMBERSOME INSTALLATION (E.G., PULLING CONDUCTORS THROUGH CONDUIT). Rigid conduit and tubing (e.g., rigid metal and nonmetallic conduit, IMC, EMT, ENT) are favorite raceway materials used to protect conductors in all types of buildings. Because it’s available in straight lengths, it must be bent to accommodate changes in direction. To prevent stretching of conductors as they are pulled through the conduit or tube, bends must be made no smaller than the minimum radius specified by code, about 6 to 8 times the conduit diameter. Typically, conduit and tubing can have up to four 90° bends or the equivalent (360° total) in one run. In runs requiring more bends, a pull box is added in the run to assist in pulling conductors and to allow access. Bends can be made at the factory or at the job site for small to medium conduits. Flexible conduit (e.g., flexible metal conduit, liquid tight flexible metal, and nonmetallic conduit) offers the advantage of easier installation and can be salvaged easily when circuits are rearranged. It’s used where mechanical protection is needed and easy relocation of equipment is desired. It can have up to four 90° bends or the equivalent (360° total) in one run. Again in runs requiring more bends, a pull box is added. Conduit should be supported to prevent wearing away against structure and to avoid stressing its end fittings. Rigid conduit and tubing must be supported within 3 ft of a box or other connection and at intervals of 10 ft (about 3 m). If it’s continuous, metal conduit can be used as the grounding conductor. Flexible conduit must be supported every 4 to 6 in (1.35 m) and within 12 in (300 mm) of a box, except up to 36 in (about 1 m) is allowed at usage points where flexibility is required (e.g., a pump motor or air conditioner condensing unit) and 6 ft (about 2 m) between a recessed light fixture and a box. If it’s continuous and properly bonded, IMC and EMT can be used as the grounding conductor. Rigid nonmetallic conduit and tubing (ENT) cannot be used as the grounding conductor. With a few exceptions, a grounding conductor is required for flexible conduit. The grounding conductor can be bare or insulated. Rigid nonmetallic conduit and tubing is manufactured from thermoplastics that have very high rates of thermal expansion (over 6 in for a 100°F temperature change per 100 ft/over 300 mm in a 50°C temperature change per 30 m). Provisions must be made if it’s exposed to significant temperature changes. Nonmetallic-sheathed cable (NM and NMC) is permitted in single- and multifamily dwelling units and some other buildings. It cannot be used underground, in buildings that are more than three stories above grade or in commercial garages, motion picture studios, theaters, places of assembly, elevator hoist ways, and other corrosive or hazardous locations. NM and NMC must be sup ported every 4_-6_ (1.35 m) and within 12 in (300 mm) of a box. Armored cable (AC) is for use in dry, indoor applications. It’s not allowed in commercial garages, motion picture studios, theaters, places of assembly, elevator hoistways, and other corrosive or hazardous locations. Bends in armored cable are limited to no less than five times the diameter. It must be supported every 4 to 6 in (1.35 m) and within 12 in (300 mm) of a box, except up to 24 in (600 mm) is allowed at points of usage where flexibility is required (i.e., at a pump motor). AC cannot be em bedded in masonry, concrete, or plaster. Conduit and cable should be installed away from locations where building occupants might use it as a handhold or footstep. Drain holes should be provided at the lowest point in a conduit run. Drilling and culling burrs should be carefully removed to prevent damage to conductor insulation. Box/Enclosure Requirements All electrical connections must be made in a protective enclosure such as a panelboard, junction, or device box, fixture, or appliance. Every switch, outlet, and connection must be contained in an electrical box and every lighting fixture must be mounted on a box. All wiring must begin or terminate at a panelboard or in a box that is housing a switch, luminaire connection, receptacle, conductor junction, or some similar terminal fitting. Junction boxes must be mounted so that the blank cover plate is visible and readily accessible. All electrical boxes must be adequately secured to the building structure. ===== Tbl. **8 RECOMMENDED MAXIMUM NUMBER OF CONDUCTORS TO ENTER ELECTRICAL BOXES OF SELECTED SIZES. SIMILAR Tbl.S EXIST IN THE ELECTRICAL CODE. VALUES SUGGESTED IN THIS Tbl. ARE LESS THAN THOSE TYPICALLY ESTABLISHED AS MAXIMUM VALUES IN THE ELECTRICAL CODE. THE RECOMMENDED MAXIMUM VALUES PROVIDED ALLOW FOR LESS CUMBERSOME CONNECTIONS WITHIN THE ENCLOSURE/BOX. Recommended Maximum Number of Conductors Enclosure/Box Dimensions Entering an Enclosure/Box by Gauge (AWG) Length Height Depth Enclosure/Box Type Round or 4 Octagonal (Lighting Boxes) Square (Device Boxes) Rectangular (Device Boxes) ===== There are no requirements that specify that a certain type of electrical box be installed for a specific purpose. The typical trade practice is to install octagonal and round boxes for lighting outlets and to install rectangular and square boxes for switches and receptacle outlets. Round boxes are normally in stalled overhead for lighting installations. However, almost any box can be used for any purpose. Conductors in an electrical box must have sufficient open air space to prevent overheating. Thus, the more conductors and/or the conductor size, the bigger the box must be. The capacity of a box, in cubic inches, is determined by its length, width, and depth. An increase in one or more of these dimensions increases box capacity. Some boxes are designed so they can be ganged together to increase box capacity. The size and number of conductors to be installed in a box influences selection of type of box and box size. By convention, a conductor that runs through the box is counted as one conductor and each conductor that terminates in the box counts as one. Fixture wires and conductors that don’t leave the box, such as an internal grounding wire, are not counted. One conductor is deducted for one or more grounding conductors that enter the box. Tbl.8 recommends the maximum number of conductors allowed to enter electrical boxes of selected sizes. Similar tables exist in the electrical code. These recommended values are less than those typically established as maximum values in the electrical code. They are recommended maximums because they allow for less cumbersome installation (e.g., making connections) and are based on industry experience. They allow for future expansion (adding connections). Ex. **10 Recommend the maximum number of No. 12 AWG THWN conductors that can enter a 4 in _ 4 in _ 1 1/2 in square electrical box, based on information in Tbl.8. From Tbl.8, 10 No. 12 AWG THWN conductors are the minimum number recommended. Ex. **11 Recommend the minimum square box size for six No. 8 AWG THWN conductors entering the box, based on information in Tbl.8. From Tbl.8, a 4 in _ 4 in _ 1 1/2 in square box is the minimum recommended. Prev: Conductor
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