- - AGRICULTURE CORE CURRICULUM - - (CLF2000) Advanced Core Cluster: AGRICULTURAL MECHANICS (CLF2650) Unit Title: ELECTRICITY ___________________________________________________________________________ (CLF2656) Topic: Simple Circuit Installation Time Year(s) 3 hours 1 / 2 / 3 / 4 ___________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the students will be able to: Learning Outcome #: (N-9) - Complete wiring of light and convenience circuits. Special Material and Equipment: Hand tools suitable for electrical wiring, cable ripper, wire stripper, 14-2 w\g cable, switch box, octagon box, single-pole switch, porcelain lamp holder, duplex receptacle, switch cover, outlet cover, wire nuts, ground clips, electrical tape References: Cooper, E. L. (1987). AGRICULTURAL MECHANICS: FUNDAMENTALS AND APPLICATIONS. Albany, NY: Delmar Publishers. Erpelding, L. H. (1971). AGRIBUSINESS ELECTRICAL LESSON PLANS. Danville, IL: Interstate Printers & Publishers. Evaluation: Quiz by instructor. TOPIC PRESENTATION: Simple Circuit Installation A. Fundamentals of Electric Circuits 1. Circuit Terms a. Simple Circuit -- A simple circuit is a complete circle of current flow. It consists of a source of electricity, one wire to carry the current from the source to where it will be used, and another wire to carry it back, plus an object of rated resistance (for example, a lamp) to use the current. b. Branch circuit--Branch circuits are circuits beginning from the service entrance panel and branching out into a variety of places for a variety of purposes. b. Open circuit--An open circuit refers to a break in the circuit circle so that the current cannot flow through it. c. Short circuit--A short circuit is a current flow around the circuit resistance and back to the source so rapidly that fuses blow, wire insulation burns, and batteries drain. d. Grounding--Grounding is the practice of providing an additional connection between a piece of electrical equipment and the earth with a conductor called a ground wire in case the current gets out of the circuit. 2. Components of a Simple Two-wire Circuit a. Wires--A simple circuit has a white wire and a black wire. 1) The white wire is known as the neutral or grounded wire because it is always connected to an underground water pipe or a ground rod through the service-entrance panel. a) It must always run direct to every 120-volt outlet. b) It must always be connected to a neutral terminal (silver-colored). c) It never has a fuse or breaker. d) It never has a switch. e) It must be electrically continuous. 2) The black wire is referred to as the "hot" wire. a) One black wire and one white wire must run to every outlet. b) Electrical potential always exists between the black wire and the white wire. b. Electrical Boxes--These are boxes made of either metal or plastic, rectangular or octagonal in shape, which have the following functions: 1) They anchor the cable or conduit so stress cannot be placed on wire connections. 2) They are nailed, screwed, or clamped to the building in order to support outlets, switches, or fixtures. 3) They contain all wire connections made outside of fixtures. c. Outlets--The most common outlet is the duplex receptacle wired so that both of its outlets are on the same circuit. 1) Outlets are wired across the black wire and the white wire. 2) The current enters the outlet on the black wire, flows from one screw through a metal strap to the other screw, and continues on to the next electrical box. 3) The two outlets in a duplex receptacle may be wired to two different circuits by breaking the metal strap between the two screws. d. Fixtures--They are bases or housings for light bulbs, fan motors, and other such electrical devices. e. Switches--They are electrical devices which provide a means to open a circuit to stop electron flow to outlets or lights and to close it again to allow current flow. 1) Switches are always wired to the black (hot) wire. 2) Their amperage and voltage ratings must match those of the circuit. 3) Their number of poles indicates how many hot wires feed through the switch. 4) Their number of throws indicates from how many locations a switch can be operated. f. Overcurrent Protection Devices--Fuses and breakers are always wired to the black (hot) wire. g. Entrance Switch--It is a switch placed ahead of the fuse in the hot wire where electricity enters the building. 3. Colors of Wires and Terminals in Structural Wiring a. Colors of Wires 1) White (sometimes natural gray) colored wire must be used only for the ground wire. 2) Additional grounding conductors may be green, green with one or more yellow stripes, or a bare wire. 3) Wiring for the "hot" wires may be any other color but it is most frequently black or red. 4) The color schemes most often used for structural wiring are: a. Two wire circuit - white and black b. Three wire circuit - white, black, and red c. Four wire circuit - white, black, red, and blue d. Five wire circuit - white, black, red, blue, and yellow b. Colors of Terminals on Electrical Equipment 1) Natural copper or brass terminals are for "hot" wires only. 2) Terminals of a whitish color (such as nickel, tin, or zinc-plated) are for grounded wires only. 3) Terminals of a green color are for grounding wires only. a. Grounding wires are those connected to the surface or shell of an appliance or tool to supply a continuous low resistance path to ground should the surface of the tool or appliance accidentally become energized B. Wiring a Convenience Circuit 1. Wiring Boxes with 12-2 G Romex Cable: a. Fasten the boxes securely to the framing. b. Drill holes in the framing through which the cable is to be pulled. c. Run the cable between the boxes and secure them with staples within 12 inches of the boxes. d. Prepare the cable for insertion into the boxes by slitting 6 to 8 inches of the outside cable covering (jacket) with a knife or cable ripper. e. Separate the wires from the ripped jacket and cut off the excess jacket material. f. Insert the ends of each cable through a knockout hole in a box leaving six inches extending from the box. g. Tighten the cable clamp to secure the cable to the box with 1/16 inch of the cable jacket extending into the box beyond the clamp. 2. Wiring a Duplex Receptacle a. Remove about 3/4 inch of insulation from the ends of the black and white wires extending from the box. Use a knife or wire stripper, but do not nick the wires. b. Make a round loop in the end of each wire with needle-nose pliers. c. Wrap the loops of the black wires around the yellow screws of the receptacle in the direction the screw turns, and then tighten the screws. d. Wrap the loops of the white wires around the white screws of the receptacle in the direction the screw turns, and then tighten the screws. e. Wrap the loop of the bare wire around the green screw of the receptacle in the direction the screw turns, and then tighten the screw. f. If a second bare wire from another cable is in the same box, secure it to the other bare wire with a special metal crimp clamp. g. Secure the receptacle with the screws provided and install the receptacle box cover. C. Wiring a Light Circuit 1. Wiring a Light Fixture Between the Source and the Switch a. Strip 5/8 inch insulation from the ends of all the wires in the octagonal junction box to prepare them for connection with wire nuts (solderless connectors). b. Strip 5/8 inch of insulation from both ends of an 8-inch length of green wire and ground it to the box with a ground clip or screw. c. Bundle the four ground wires together and twist a wire nut onto the four wire ends. d. Mark the white wire coming from the switch with black tape to identify it as a hot wire. e. Attach the black wire from the switch to the yellow terminal of the light fixture. f. Strip 5/8 inch of insulation from both ends of an 8-inch length of white wire and attach one end to the white screw of the light fixture. g. Connect the loose ends of the three white wires with a wire nut. h. Connect the ends of the remaining black wires--including the white wire wrapped in black tape--with a wire nut. 2. Wiring a Single Pole, Single Throw Switch for the Light Above a. Remove about 3/4 inch of insulation from the ends of the black and white wires running to the switch from the light. b. Make a round loop in the end of each wire with needle-nose pliers. c. Wrap black tape around the white wire to identify it as a black or hot wire. d. Wrap the loops of the black wires around the yellow screws of the receptacle in the direction the screw turns, and then tighten the screws. e. Attach the bare ground wire to the box with a ground clip (gee clip). f. Secure the switch in the box with screws provided and install the switch cover. _________________________________________________________ ACTIVITY: 1. Wire a convenience and light circuit. 2. Diagram the light circuit. _________________________________________________________ 6/26/91 OLR/tf #%&C