7ba53ca448b6760d68857d8f2c99984e.ppt
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Electrical Principles and Wiring Materials Unit #31
Principles of Electricity is a form of energy that can produce light, heat, magnetism, chemical changes n Resistance: tendency of a material to prevent electrical flow n Conductor: if electricity flows easily n Insulator: material that provides great resistance n
Amps, Volts, Watts Amperes: measure of the rate of flow of electricity in a conductor n Volts: measure of electrical pressure n Watts: measure of the amount of energy or work that can be done n Ohms: measure of electrical resistance to flow n
Ohm’s Law Ohm = R n Volts = E n Amps = I n Ohm’s Law: E = IR n I=E/R R=E/I
Electrical Safety Shock and Fire n Never disconnect any safety device n Don’t touch electrical items with wet hands or feet n Don’t remove ground plug prong n Use GFI in wet areas n Discontinue use of extension cord that feels warm n Don’t put extension cords under carpet n
Electrical Safety Install wiring according to NEC n Blown fuse or breaker, determine cause n Don’t replace fuse with larger fuse n Don’t leave heat producing appliances unattended n Heaters & lamps away from combustibles n Don’t remove back of TV (30, 000 v when off) n Electric motors lubricated, free of grease etc. n
Electrical Safety Keep appliances dry n Don’t use damaged switches, outlets, fixtures, extension cords n Follow manufacturer’s instructions for installation and use of electrical equipment n
Service Entrance Power from power company n Transformer: drops volts from 25, 000 volts to 240 volts n Service drop: wires etc from transformer to house n Entrance head: weather-proof at house n Meter: $$$ n Service Entrance Panel (SEP): box with fuses or breakers n
Electric Meter Kilowatthours: how electricity is sold n Kilo = 1000 n Watthour = use of 1 watt for one hour n n 100 watt light bulb for 1 hour - 100 watthours n Kilowatthour = 1000 watts for one hour
Branch Circuits usually begin at SEP n branch out into a variety of places n only 1 motor or; n series of outlets or; n series of lights n use correct size wire and fuse or breaker n
Types of Cable Nonmetallic sheathed cable: copper or alluminum wire covered with paper, rubber, or vinyl for insulation n Armored cable: flexible metal sheath with individual wires inside. Wires are insulated n Conduit: tubing with individually insulated wires n
Wire Type and Size copper n No 14 (14 gauge) = 15 amp circuits n No 12 = 20 amps n No 10 = 30 amps n aluminum use one size larger n lower gauge number = larger wire n No 8 and larger use bundles of wires n current travels on outer surface of wire, so a bundle of smaller wires can carry more n
Voltage Drop loss of voltage as it travels along a wire n lights dim, motors overheat n larger wires have less voltage drop for a given amount of current n longer wire = greater problem n must increase wire size as distance increases n
Wire Identification Type of outer covering, individual wire covering, cable construction, number of wires n Wire type stamped on outer surface n
Wire Types Type T - dry locations/Thermoplastic locations/ n Type TW - dry or wet/Moisture Resistant wet/ Thermoplastic n THHN - dry, high temps n THW and THWN - wet, high temps n XHHW - high moisture & heat resistance n UF - direct burial in soil but not concrete n
Electrical Conductors n n n R Rubber Insulation RH Heat Resistant Rubber RW Moisture Resistant Rubber Ru Latex Rubber Ru. A Latex Rubber with Asbestos Sub. These are primarily for individual wires. If we have multiple wires fastened together it is called a cable.
Wire Identification n n Color coded: black, red, & blue = positive or hot wires which carry current to appliances White = neutral wires carry current from appliance back to source Green or Bare = ground all metal boxes and appliances *Never touch any of these wires together unless you are instructed to do so.
Wire Identification Wire Size: 12 -2 has two strands of No. 12 wire (black & white) n 12 -2 w/g same, with one green or bare n 12 -3 has three strands of No. 12 (black, red, white) n 12 -3 w/g same, with green or bare n
More Electrical Safety "Shocking Statistics“ n n More than a thousand people are killed in accidental electrocutions and fires caused by faulty electrical systems every year. Thousands more are shocked and burned as the result of accidental contact with electricity every year. An estimated $1. 3 billion in property damage occurs each year due to faulty use of electricity. From http: //www. safeelectricity. org/results. asp? ID=115
Electrical Safety n Proper use of extension cords n Stay away from wet areas, sharp objects heat & oil n Check cords periodically for nicks and cuts n Always use the correct wire gauge and cord length for its intended use: Up to 35’ use # 14 gauge wire n 36’ to 75’ use # 12 gauge wire n 76’ to 100’ use #10 gauge wire (All cords are on 110 -120 volt ) n
Electrical Safety Power Tools If possible always buy grounded, 3 -prong power tools (ground included) If tools are not available purchase double-insulated power tools, (2 layers of insulation to protect against shock) Always make sure tool are UL listed for safety Handle tools and their electrical cords with care n n n
Wire Protection n n Always follow National Electrical Code with the local building code Encase in outdoor wire in conduit Use conduit & groundfault circuit interrupters (GFCI) in damp locations Keep any unprotected wire away from livestock, children etc.
In Case of Electrical Accident Always use fire extinguisher in case of fire n Immediately turn off electrical power source n Apply CPR if necessary n Find help as quickly as possible n