xi Chapter 3 Tools 33 Copyright Goodheart-Willcox Co., Inc. 3.1.2 Sawing Tools Sawing tools are needed to cut materials and remove obstructions. The requirements of the specifi c task determine whether a handsaw or power saw is used. Be sure the selected saw is appropriate for the task. Keep your saws well maintained. Follow the tool care instructions in the owner’s manual. Always work with a sharp blade. At the very least, a dull blade forces you to work more slowly. A dull blade can also bind in the mate- rial, making cutting more dangerous. Force is required to propel the saw through the cut, but be careful not to use too much force. Let the blade do the cutting and do not rush it. Trying to rush through the cut by forcing the saw puts added pressure on the blade and could cause the blade to break. Always wear gloves and safety glasses when sawing. This protects your hands and eyes from any loose particles. Figure 3-3 summarizes these safety rules for cutting tools. Many different types of saws are used by electricians. These include both handsaws and power saws. The following are some of the more commonly used saws and some of their uses (Figure 3-4): • Handsaw—Used to trim studding or modify joists to accommodate panels, boxes, and fi xtures. A fi ne-tooth handsaw can be used to cut PVC conduit. SAFETY NOTE Never use a hammer that has a loose or dam- aged head. • Keyhole saw—Handy for making neat, accurate openings in drywall for receptacle boxes. • Reciprocating saw—Used for heavy-duty sawing into wooden and metal structural members. • Band saw—Needed to cut through heavy- gage metal framing and structural steel. They are also used to cut conduit and metal supports. • Hacksaw—This saw can be used to cut conduit and metal obstructions. • Hole saw—This cylindrical saw is mounted on an auger with a pilot drill. The auger is then fi tted into an electric drill. The saw is used to cut holes in wood and other materials. 3.1.3 Fastening Tools The most popular fastening tools are screw- drivers and wrenches. Screwdrivers are used to install and tighten screws in terminal blocks and devices, such as receptacles, fi xtures, boxes, box covers, and panels. They should be insu- lated when used for electrical work. Screwdrivers are designed to install and remove screws. Do not use a screwdriver for chiseling or prying. Never strike a with a hammer. Wrenches are another versatile tool used by electricians to fasten items. There are numerous types and styles available. Most wrenches are CAUTION Hole saws are operated at diff erent speeds for diff erent materials. Be sure to check the manu- facturer’s information for the correct speed. CAUTION The size of the screwdriver should be appropri- ate for the Using the wrong screw- driver can cause damage to the screwhead and the screwdriver.(uncoated) Goodheart-Willcox Publisher Figure 3-3. Summary of basic cutting tool safety rules. Cutting Tool Safety • Wear gloves and safety glasses when using cutting tools. • Use the correct size and type of cutting tool for its designed purpose. • Never force a cutting tool past reasonable pressure. • Keep cutting edges sharp. b d fi fi fi h h d fi remove screws. Do not use a screwdr sscrewdriverwcre o ol u e nu renc e app ssize ize whea b d fi A fi fi h h d fi s o e r e s w Chapter 6 Conductors 99 Copyright Goodheart-Willcox Co., Inc.. SAMPLE PROBLEM 6-5 Problem: Determine the voltage drop on a 20-amp circuit having a length (one-way) of 170 ′screw. , 10 AWG THW stranded copper conductors, and a single-phase, 120-volt power supply. Solution: From Table 8 of Chapter 9, the resistance for 10 AWG stranded copper conductor is 1.24 ohm/kFT. 18 18 16 16 14 14 12 12 10 10 8 8 1 7 1 7 1 7 1 7 1 7 1 7 — 0.39 — 0.49 — 0.62 — 0.78 — 0.98 — 1.23 1.02 1.16 1.29 1.46 1.63 1.85 2.05 2.32 2.588 2.95 3.264 3.71 0.040 0.046 0.051 0.058 0.064 0.073 0.081 0.092 0.102 0.116 0.128 0.146 0.001 0.002 0.002 0.003 0.003 0.004 0.005 0.006 0.008 0.011 0.013 0.017 7.77 7.95 4.89 4.99 3.07 3.14 1.93 1.98 1.21 1.24 0.764 0.778 8.08 8.45 5.08 5.29 3.19 3.26 2.01 2.05 1.26 1.29 0.786 0.809 42.0 42.8 26.4 26.9 16.6 16.9 10.45 10.69 6.561 6.679 4.125 4.204 12.8 13.1 8.05 8.21 5.06 5.17 3.18 3.25 2.00 2.04 1.26 1.28 26.5 27.7 16.7 17.3 10.4 10.7 6.57 6.73 4.148 4.226 2.579 2.653 25.5 26.1 16.0 16.4 10.1 10.3 6.34 6.50 3.984 4.070 2.506 2.551 0.823 1.06 1.31 1.68 2.08 2.68 3.31 4.25 5.26 6.76 8.37 10.76 — 0.015 — 0.019 — 0.024 — 0.030 — 0.038 — 0.049 1620 1620 2580 2580 4110 4110 6530 6530 10380 10380 16510 16510 0.823 0.823 1.31 1.31 2.08 2.08 3.31 3.31 5.261 5.261 8.367 8.367 Table 8 Conductor Properties Area ohm/ km ohm/ kFT ohm/ kFT ohm/ km ohm/ kFT Uncoated Area Diameter Diameter Stranding Copper Aluminum Overall Conductors Direct-Current Resistance at 75°C (167°F) Coated ohm/ km Circular mils Quantity mm in. mm2 in.2 mm2 Size (AWG or kcmil) mm in. Copyright © 2019 NFPA Using the equation presented in the previous discussion: VD = 2 × L × I × R ______ 1000 = 2 × 170′ × 20 A × 1.24 ohm/kFT _______________ 1000 = 8.4 V To determine the voltage drop as a percentage of the total voltage, divide the voltage drop by the total voltage: 8.4 V ___ 120 V = 0.07 = 7% The Code recommends a maximum 3% voltage drop. It would be advisable rewire this circuit using a No. 6 AWG copper conductor, which would reduce the voltage drop to an acceptable VD = 2 × 170′ × 20 A × 0.491 ohm/kFT ________________ 1000 = 3.3 V Checking the voltage drop as a percentage of the total voltage: 3.3 V ___ 120 V = = This is acceptable.. Safety Notes alert you to potentially danger- ous materials and practices. Cautions alert you to practices that could potentially damage equip- ment or instruments. Sample Problems present practical, real-world example problems followed by clearly explained solutions. End-of-Chapter Content End-of-chapter material provides an opportuni- ty for review and application of concepts. A con- cise Summary provides an additional review tool that reinforces key learning objectives. This helps you focus on important concepts present- ed in the text. Know and Understand questions enable you to demonstrate knowledge, identifi - cation, and comprehension of chapter material. Apply and Analyze questions extend learning and help you analyze and apply knowledge. Critical Thinking questions develop higher- order thinking and problem-solving, personal, and workplace skills. Know the Code questions help you gain knowledge of and become com- fortable with the NEC. t-W - Will lcoox Co ., Inc 0.07 7% commends mm a maxim um 3% volta ge drop . It w ould b e advi sable tto to rew ire th is cir cuit u sin g a o pp pper conductor, w h ich wo u ld red uce t h e vol ta ge d rop to an a ac cepta ble llevel:l:e ev 2 2 × 170 ′ × 20 A × 0.491 o m/ k T _______________F_ 1000 3.3 V e volta ge dro p as a percentage o f the total volta ge: 00.0275 . 02 75 22.75%7. 5% table 136 Modern Commercial Wiring Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. Summaryh • Electrical service is the system of conductors extending from the utility pole or equipment to a facility’s service equipment. These service conductors must be run either overhead (service drop) or underground (service lateral). • The Code has minimum vertical clearance requirements for service drops. • Service conductors must have an ampacity rating equal to or greater than the intended load. • All buildings must have a means of disconnecting all power feeders from the service-entrance conductors. Depending on voltage, these disconnects will require a certain amount of workspace clearance. • The power utility company provides numerous voltage levels that can be changed by transformers to meet specifi c needs. Know and Understand Answer the following questions using the informa- tion provided in this chapter. 1. True or False? A facility’s service equipment is considered part of the service. 2. What is the minimum vertical clearance below service-drop conductors above a fl at roof that is not subject to vehicular traffi c? A. 6′ B. 8′ C. 12′ D. 18′ 3. What is the minimum vertical clearance below service-drop conductors passing over a parking lot? A. 6′ B. 8′ C. 12′ D. 18′ 4. True or False? A service drop is run underground. 5. True or False? The maximum height above grade for the handle for a service disconnect is 8′. 6. True or False? A maximum of six service disconnects may be installed for each service. 7. Which article in the Code contains the requirements for workspace clearances around large (over 600-volt) services? A. Article 440 B. Article 220 C. Article 110 D. All of the above. Apply and Analyze 1. What is the importance of a drip loop? 2. What are the support requirements for service-entrance cable between the service head and the meter? Critical Thinking 1. Why are you prohibited from placing service equipment in bathrooms, storerooms, closets, or damp cellars? Know the Code Refer to the National Electrical Code to answer the following questions. 1. What is the minimum size for overhead service-drop conductors and service- lateral conductors? 2. Which Code section specifi es minimum burial depth of service-lateral conductors? 3. Which Code section prohibits service conductors passing through one building to serve another building or structure? 4. Ungrounded service conductors must have overcurrent protection. Where is this overcurrent protection located? 5. For aboveground service-entrance conductors exceeding 1000 volts, which Code sections list the approved wiring methods?