CHAPTER III Show ELECTRICAL WIRING COMPONENTS 3.1 –BASIC WIRING TOOLS When wiring or testing the electrical system in buildings, a wide variety of tools are used. The most common employed tools are the following. Screwdrivers. Intended to tighten or loose screws. They are available in a variety of sizes and shapes. Figure 3.1 shows in a) different flat-blade screwdrivers, and in b) Phillips screwdrivers are shown.
 Figure 3.1. Screwdrivers. a) flat-blade Screwdrivers, b) phillips Screwdrivers A very useful screwdriver for electrical installations is the one shown in Figure 3.2. It is basically a flat-blade screwdriver, but the blade is protected as shown to make it easier to fix the connectors and couplings.
Figure 3. 2. Special Screwdriver for electrical wiring Pliers. Each type of work require a specific type of pliers. Figure 3.3 shows a variety of the types most employed in electrical installations. Figure 3.3. Pliers. a) long-nose; b) side cutting; c) crimping tool-wire stripper; d) tongue & groove Hammers. The most commonly used hammer by electricians is the claw hammer, as shown in Figure 3.4. Typical used weights are 16 oz. and 20 oz. From the safety point of view, it is important to use non-conductive materials for the handle.
Figure 3.4. Hammers. a) curved claw, b) straight claw SawsSaws are frequently used in electricians job. The more frequently employed saws are the hacksaw and the compass saw (Figure 3.5). The hacksaw is used to cut pipes, and the compass saw is used when the electrician has to cut an irregular shape in a wood or drywall structure.
Figure 3.5. Saws. a) Hacksaw. b) Compass saw Fish tapeThe steel tape is used for passing wires through pipes. The tape is passed through the pipe until it appears on the other end. The wires are tied at the end of the tape, and then the tape is pulled from the place where it was entered into the pipe, passing at the same time the wires through the pipe (Figure 3.6).
Figure 3.6. Fish tape Measuring ToolsThe measuring tool preferred by most electricians is the steel tape as can be seen in Figure 3.7. Different lengths are available depending on the job characteristics.
Figure 3.7. Steel Tapes Several wenches are shown in Figure 3.8. The use of each type will depend on the work being realized and on the person's preferences.
Figure 3.8. Wrenches. a) pipe; b) chain; c) open end; d) box end; e) adjustable; f) socket set; g) nut driver Tubing BendersWhen it is necessary to bend rigid metallic conduits, the bend can be made using special bending tools. Bends in 1/2 –inch, ¾-inch, and 1-inch conduit can be made using hand benders, Figure 3.9. Hydraulic benders must be used to make bends in larger sizes of conduit. Figure 3.9. Tubing benders. Besides the enumerated, there are a number of tools used in electrical jobs. Some of them are showed in Figures 3.10, 3.11, and 3.12. Figure 3.10. Level
Figure 3.11. Chisel
Figure 3.12. Knife. To increase productivity and reduce the needed effort in performing tasks, almost all the described hand tools have it's electrical counterpart. The drill showed in Figure 3.13 is extremely important for the electrician's job. The cordless drill is more frequently used. Employed not only for drilling holes through walls or other parts of the structure, but also using special bits as powered screwdrivers, etc.
Figure 3.13. Cordless Drill. a) cordless drill; b) rechargeable power source 3.2 –WIRING METHODS AND MATERIALS The National Electrical Code® (NEC®) permits the use of different wiring methods. Chapter 3 on the National Electrical Code® covers this part. The selection of some specific method depends on the type of building, location, desired quality, etc. Before analyzing the different wiring methods it is useful to pay attention to the used sizes and insulations in the conductors for general wiring. 3.2.1. -CONDUCTORS FOR GENERAL WIRING The material employed in the conductor construction, according to NEC®, shall be aluminum, copper-clad aluminum or copper unless otherwise specified. Conductors shall be insulated. Table 310-13 of the NEC®-1999, lists various types of insulated conductors covered by the requirements of the code. From the table information may be obtained related to the trade name, type letter, maximum operating temperature, application, type of insulation and size. To clarify ideas, a partial reproduction of the table is presented in Figure 3.14.
Figure 3.14. Partial Reproduction of Table 310.13 (Conductor Application and Insulation) from the NEC®-1999. Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the referenced subject which is represented only by the standard in its entirety. The conductor ampacity is the maximum number of amperes allowed for that conductor under specified working conditions. The conductor used must have sufficient ampacity or capacity to carry the load being served. The limiting factor for the conductor's ampacity is the heat dissipated in the wire due to the passing current. It is calculated by P = I2R watts. The wire insulation and location as well as the metal used for its construction will determine its capacity to carry the electrical current. Allowable ampacities of insulated conductors, rated 0 through 2000 Volts, are presented in Tables 310-16 through 310-20 from NEC®-1999. Table 310-16, is partially shown for copper conductors and AWG values in Figure 3.15, is widely used in electrical wiring calculations and will be given special attention.
Figure 3.15. Partial Reproduction of Table 310-16 (Allowable Ampacities of Insulated Conductors) from NEC®-1999. Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the referenced subject which is represented only by the standard in its entirety. The conductor size is expressed using the American Wire Gauge (AWG) denomination. Note that as the size increases, the number decreases until the # 1 denomination is reached. From # 1/0, there is an increase of the number with the size. For sizes bigger than 4/0(not represented in Figure 3.15), the size is expressed in cmil. For conductors with an * sign, Section 240-3 of the NEC® does not allow (unless specifically permitted) overcurrent protection exceeding 15 amperes for #14, 20 amperes for #12, and 30 amperes for #10. This means that independently of the indicated ampacity for these conductors in Table 310-16, the number of amperes cannot exceed the specified in Section 240-3. Table 310-16 also includes temperature correction factors (not shown in Figure 3.15). These correction factors shall be applied for ambient temperatures other than 30oC (86oF). Figure 3.16 shows conductors of different sizes. All conductors are marked with the following information: the maximum rated voltage for which it is listed, letters that identify it as to type, the manufacturer’s name, and the AWG size or circular mil area. No. 14 is the smallest wire size permitted for general wiring. Figure 3.16. Sizes of Conductors 3.2.2. –ELECTRICAL RACEWAY The term raceway is defined by the NEC® as any channel for holding wires, cables, or bus bars that is designed and used for this purpose. The following will cover some of the possible methods and used materials: electrical metallic tubing, rigid metal conduit, intermediate metal conduit, flexible conduit, rigid nonmetallic conduit, electrical nonmetallic tubing, etc. Electrical metallic tubing (EMT) ( NEC®, Article358). It is a listed metallic tubing of circular cross section approved for the installation of electrical conductors when joined together with listed fittings. It's use is permitted in exposed and concealed work. There it is necessary to use corrosion protection when galvanized steel EMT extend directly from concrete encasement to soil burial. It's use is not permitted where it will be subject to severe physical damage, where protected from corrosion solely by enamel or subject to permanent moisture and for the support of fixtures or other equipment except conduit bodies no larger than the largest trade size of the tubing. The minimum permitted size is ½” and the maximum 4”. EMT shall be securely fastened in place at least every 10 feet, and at least 3 feet from any termination point (Section 358.30 (A). Figure 3.17 shows this last situation. Figure 3.17. EMT installation All cuts and ends of EMT shall be reamed to remove rough edges. The number of bends between outlets or fittings must not be greater than equivalent of four 90o bends or 360o total. The number of conductors permitted in a single pipe can be calculated knowing the useful pipe area, the area of each insulated conductor and the number of conductors. The area of insulated conductors and fixture wires is obtained from the NEC® Table 5, chapter 9. Figure 3.18 shows the areas of some conductors, extracted from this table.
Figure 3.18. Area of THHN, THWN, and THWN-2 conductors. The maximum number of conductors in a pipe shall not exceed the percentage fill specified in Table 1, Chapter 9 of NEC®, represented down.
From NEC®, table 4, chapter 9 it is possible to know the dimensions and percent area of conduits and tubing. A partial reproduction is presented in Figure 3.19.
Figure 3.19. Electrical Metallic Tubing areas Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the referenced subject which is represented only by the standard in its entirety. Example 3.1. Determine what EMT pipe size is necessary to accommodate 4 # 8, 4 # 6, 7 #10, and 6 # 12 THHN conductors. 4 x 0.0366 = 0.1464 4 x 0.0507 = 0.2028 7 x 0.0211 = 0.1477 6 x 0.0133 = 0.0798 Total area = 0.5767 As there are more than 2 conductors in the pipe, the useful pipe area is 40% of its total area. The useful pipe area shall be greater than the conductors area (0.5767). Checking for 1¼” : 1.496 x 0.4 = 0.5984 (this number may be obtained directly from Table 4). As 0.5984 > 0.5767, the selected pipe is acceptable. The bending of EMT requires an EMT bender. EMT pipes are coupled together using EMT couplings. For connection to electrical boxes there are several types of connectors used. Figure 3.20 shows some of these fittings.
Figure 3.20 EMT couplings and connectors ( NEC®, Article344). RMC is approved for use in all types of construction and atmospheric conditions. Also it is permitted as an equipment grounding conductor. The code permits its use in concrete, in direct contact with the earth or in areas subject to severe corrosive influence where protected by corrosion protection and judged suitable for the condition. The minimum size approved is ½” and the maximum 6”. The number of conductors in a conduit is given by the percentage fill from Table 1, using the conduit dimensions of Table 4, Chapter 9 of the NEC®. After the conduit is cut, it requires reaming to remove all burrs. The next step is threading the conduit with a die (Figure 3. 21).
Figure 3.21. Pipe threaders. The couplings and connectors used for the installation of rigid conduit may be threaded or threadless. The number of bends shall not be more than 360o total. Rigid conduit is supported at intervals not exceeding 10 ft or in accordance with Table 344.30(B)(2) of the NEC®. Intermediate Metal Conduit (IMC) ( NEC®, Article342). IMC is a thinner-walled rigid metal conduit that is satisfactory for use in all locations where rigid metal conduit is approved. All the fittings are interchangeable for either IMC or RMC. Galvanized IMC installed in concrete or in contact with soil does not generally require supplementary corrosion protection. The range of sizes are minimum ½”, and maximum 4”. The number of conductors in conduit, the support distance, and the number of bends follow the same rules as in previous cases. Figure 3.22 shows the minimum fastening requirements for intermediate metal conduit according to Sections 342.30(A) and 342.30(B).
Figure 3.22. Minimum fastening requirement for IMC Flexible Metal Conduit (FMC)( NEC®, Article348). Flexible metal conduit is known frequently as Greenfield. It is a raceway of circular cross section made of helically wound, formed, interlocked metal strip. The minimum permitted size is ½”, but under certain conditions, the code permits to use 3/8”. A frequent case where 3/8” flexible metal conduit is used, in lengths not in excess of 6 ft, is for connecting vibrating equipment as the garbage disposal and fluorescent lights in residential wiring,. Conduits larger than 4” are not permitted by the code. Figure 3.23 shows two places where FMC may be used.
Figure 3.23. Some places where flexible metal conduit may be used. FMC is permitted for use in wet locations under the condition of preventing water from entering enclosures or other raceways to which the conduit is connected. Often the use of FMC requires the inclusion of grounding conductors. For lengths under 6 ft and circuits not exceeding 20 amperes, it is not necessary to install the grounding conductor. The maximum distance between flexible metal conduit supports is 4 ½ ft. It shall also be fastened in place within 12” of a box or other conduit termination. The number of conductors is calculated using Table 4, Chapter 9 of the NEC®. Figure 3.24 shows some of the common used fittings.
Figure 3.24. Fittings used with flexible metallic conduit. ( NEC®, Article350). Liqidtight flexible conduit is recommended where conditions of installation, operation or maintenance require flexibility or protection from liquids or vapors penetrating the conduit. It is composed of a liquidtight, nonmetallic, sunlight-resistant jacket over an inner flexible metal core. It is used outdoors for connecting air conditioning units or indoors for connecting machinery where oil leakage may be present. Figure 3.25 shows a liquidtight conduit used in an air conditioning installation.
Figure 3.25. Installation of a liquidtight conduit. Armored Cable (AC)( NEC®, Article 320). AC is a fabricated assembly of insulated conductors in a flexible metallic enclosure. It is listed in sizes # 14 through # 1 copper and # 12 through # 1 aluminum or copper-clad aluminum for use at 600V or less. Figure 3.27 shows an example of armored cable.
Figure 3.26. Armored cable The support conditions are the same as for the FMC. It is permitted for branch circuits and feeders in both exposed and concealed work. Metal-Clad Cable (MC) (NEC®, Article 330). Type MC cable is a factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth or corrugated tube. MC cable is listed in sizes from # 18 for copper conductors and # 12 for aluminum or copper-clad aluminum conductors. Its use is permitted for up to 2000 Volts. MC cable may be used for services, feeders and branch circuits including power, lighting, control and signal circuits outdoors or indoors. MC is not supposed to be used where it will be exposed to destructive corrosive conditions or where it will be submitted to physical damage. Most applications require that MC cable be supported and secured within 12” of a box or other conduit termination and at intervals not exceeding 6 ft (Figure 3.27).
Figure 3.27. MC cable supports. Rigid Nonmetallic Conduit(NEC®, Article 352) Generally known as PVC, refers to conduit and fittings of suitable nonmetallic material that is resistant to moisture and chemical atmospheres. There exist several types of rigid nonmetallic conduit that may be used according to the specific application. It's use includes aboveground and underground installations as well as for direct burial without encasement in concrete. It is recommended for locations subject to severe corrosive influences and in wet locations. Nonmetallic conduits are not permitted in ducts, plenums and other air-handling spaces that may contribute smoke and products of combustion during a fire. Assembly of the conduit system is obtained cementing the various parts and fittings with a special solvent-type PVC cement. The bending is obtained by providing an even distribution of heat to make the conduit pliable. Nonmetallic rigid conduit shall be supported and secured within 3 ft of a box or other conduit termination and at intervals regulated by Table 352.30(B) from the NEC®, reproduced in Figure 3.28.
Figure 3.28. Support of Rigid Nonmetallic Conduit Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the referenced subject which is represented only by the standard in its entirety. Electrical nonmetallic Tubing (ENT)(NEC®, Article 362). ENT is a pliable corrugated raceway of circular cross section with integral or associated couplings, connectors and fittings listed for the installation of electric conductors. Because of the corrugation, the raceway may be bent by hand and has some degree of flexibility, but it is not intended for use in motors or other equipment to prevent transmission of vibrations. The sizes range from ½” to 2”. Figure 3.29 shows the way ENT has to be supported. It may be used in buildings not exceeding three floors above grade and for exposed work, where it is not subject to physical damage. In buildings over three floors, ENT shall be concealed within walls, floors and ceilings, providing a thermal barrier material protecting the pipe from high temperatures. Nonmetallic–sheathed Cable(NEC®, Article 334) Nonmetallic-sheathed Cable is a factory assembly of two or more insulated conductors having an outer sheath of moisture-resistant, flame retardant, nonmetallic material. It may be used for either exposed or concealed wiring. Where exposed, it cannot be subject to physical damage. There are three types of Nonmetallic –sheathed cable: NM, NMC and NMS. Each type has characteristics making it suitable for different electrical installations. Nonmetallic –sheathed cable shall be supported and secured within 12” of a box or other conduit termination and at intervals not exceeding 4 ¼ ft. figure 3.29 shows an example of Nonmetallic –sheathed cable.
Figure 3.29. Nonmetallic –sheathed cable (NEC®, Articles 376 and 378). Are sheet metal (for metallic) or flame-retardant nonmetallic troughs with hinged or removable covers for housing and protecting electric wires and cables and in which conductors are laid in place after wireway has been installed as a complete system. They are frequently are used for exposed work and it use is not permitted where subject to severe physical damage or corrosive vapor. The number of current-carrying conductors in the wireway is limited to 30 and the total cross-sectional area of all conductor will not exceed 20% of the interior cross-sectional area of the wireway. Exception No. 1 permits the number of current-carrying conductors to exceed 30, where the adjustment factor for more than three current-carrying conductors [NEC®, Table 310-15(b)(2)(a)] is applied, maintaining the cross-sectional area of all conductors less than 20% of the interior cross-sectional area of the wireway. Metallic and nonmetallic wireways shall be supported at each end and according to:
3.2.3. -ELECTRICAL BOXES Electrical boxes are available in a variety of shapes and sizes to be used according to the particular application. It is possible to find metal and plastic boxes. All metal boxes need to be grounded. Article 314 from the NEC® covers the installation and use of all boxes and conduit bodies used as outlet, junction, or pull boxes. Switch boxes are 2” x 3” in size and may be found in ranges from 1 ½ in. to 3 ½ in. Some metal boxes are gangable. That means that they have removable sides and can be mounted side by side to accommodate two or more switches or receptacles. Plastic and many metallic boxes don’t have this possibility, but they are manufactured in one-gang, two-gang, three-gang or four-gang styles. Round and octagonal metal boxes are generally used with ceiling fixtures. Metal and plastic square boxes are often used as junction boxes. When rectangular boxes are used for holding switches or receptacles, they use a flat cover with switch or receptacle shaped openings called plaster ring. Figure 3.30 shows some of the more frequently used boxes.
Figure 3.30. Types of boxes The box volume gives the number of conductors inside a box. In no case the volume of a box can be smaller than the calculated volume of the conductors filling it. The box volume is given in Table 314.16(A) for metal boxes and the volume allowance required per conductor is presented in Table 314.16(B) from the NEC®. In Figure 3.31, a partial reproduction of Table 314.16(A) is presented, and Figure 3.32 shows Table 314.16(B).
Figure 3.31. Volume of metal boxes
Figure 3.32. Volume allowance required per conductor Reprinted with permission from NFPA 70-1999, the National Electrical Code®, Copyright© 1998, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the referenced subject which is represented only by the standard in its entirety. For calculating the box size it is necessary to take into account:
Example 3.2. Select the rectangular box necessary to accommodate: 3 # 12, 2 # 10,and 2 # 8 conductors, one # 12 , and one #10 ground. 3 x 2.25 = 6.75 2 x 2.5 = 5.0 2 x 3.0 = 6.0 1 x 2.25 = 2.25 1 x 2.5 = 2.5 Total 22.5 cu. in. A (4 11/16 x 1¼) square is acceptable 3.3. REVIEW QUESTIONS 3.1. Insulated handles are important on many electrician’s tools because_________________. 3.2. Why must all joints, connections, and splices be contained in a box? 3.3. List four shapes of boxes 1. ______________ 2. ______________ 3. ______________ 4. ______________ 3.4. NEC® requires a grounding bushing wherever conduit enters a non-threaded opening on a box. a) True b) False 3.5. A #8 copper wire THWN has an ampacity of __________Amps. 3.6. What size box is needed when there are two #10 AWG conductors, six #12 AWG conductors, and four #14 AWG conductors? 3.7. What size box is needed to install four # 12 conductors, two # 14 conductors, four grounding conductors, and three cable clamps? 3.8. When a receptacle is installed in a metallic box it must always be connected to ground through the grounding hex screw. a) True b) False 3.9. As the AWG number becomes smaller, the wire size becomes a) Larger b) Smaller 3.10. When using a #12 THWN copper wire in a branch circuit, the over-current protection shall not exceed ___________Amps. 3.11. The maximum number of conductors # 12 that can be allocated in a 4 x 1¼ square box is ____________. 3.12. The allowable ampacity for a # 2/0 THHN copper wire is __________Amps. National Electrical Code® and NEC® are registered trademarks of the National Fire Protection Association, Inc., Quincy, MA 02269 |
What percent of a metal Wireway cross section may be occupied by splices taps and conductors at any point?
Pos Terkait
Copyright © 2024 ketiadaan Inc.
