Electrical Principles and Wiring Materials Unit #31

Principles of Electricity n 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

Amps, Volts, Watts n 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

Ohm’s Law n Ohm = R n Volts = E n Amps = I n Ohm’s Law: E = IR I=E/RR=E/I

Electrical Safety n 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

Electrical Safety n 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 (30,000v when off) n Electric motors lubricated, free of grease etc.

Electrical Safety n 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

Service Entrance n 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

Electric Meter n Kilowatthours: how electricity is sold n Kilo = 1000 n Watthour = use of 1 watt for one hour n 100 watt light bulb for 1 hour watthours n Kilowatthour = 1000 watts for one hour

Branch Circuits n 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

Types of Cable n 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

Wire Type and Size n 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

Voltage Drop n 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

Wire Identification n Type of outer covering, individual wire covering, cable construction, number of wires n Wire type stamped on outer surface

Wire Types n Type T - dry locations/ n Type T - dry locations/Thermoplastic n Type TW - dry or wet/ n Type TW - dry or wet/Moisture Resistant 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

Electrical Conductors n n RRubber Insulation n n RHHeat Resistant Rubber n n RWMoisture Resistant Rubber n n RuLatex Rubber n n RuALatex Rubber with Asbestos Sub. n n These are primarily for individual wires. If we have multiple wires fastened together it is called a cable.

Wire Identification n Color coded: black, red, & blue = positive or hot wires which carry current to appliances n White = neutral wires carry current from appliance back to source n Green or Bare = ground all metal boxes and appliances n *Never touch any of these wires together unless you are instructed to do so.

Wire Identification n 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

More Electrical Safety More Electrical Safety "Shocking Statistics“ n More than a thousand people are killed in accidental electrocutions and fires caused by faulty electrical systems every year. n Thousands more are shocked and burned as the result of accidental contact with electricity every year. n An estimated $1.3 billion in property damage occurs each year due to faulty use of electricity. n From

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: n 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 volt )

Electrical Safety n Power Tools n If possible always buy grounded, 3-prong power tools (ground included) n If tools are not available purchase double-insulated power tools, (2 layers of insulation to protect against shock) n Always make sure tool are UL listed for safety UL listed UL listed n Handle tools and their electrical cords with care

Wire Protection n Always follow National Electrical Code with the local building code National Electrical Code National Electrical Code n Encase in outdoor wire in conduit n Use conduit & ground- fault circuit interrupters (GFCI) in damp locations n Keep any unprotected wire away from livestock, children etc.

In Case of Electrical Accident n 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