Presentation on theme: "Electrical Principles and Wiring Materials"— Presentation transcript:
1 Electrical Principles and Wiring Materials UNIT 33
2 Principles of Electricity Electricity is a form of energy that can produce light, heat, magnetism, chemical changesResistance: tendency of a material to prevent electrical flowConductor: if electricity flows easilyInsulator: material that provides great resistance
3 CONDUCTORS SILVER-premium conductor (too expensive) COPPER-very good conductorALUMINUM-good conductor(outside)
4 Amps, Volts, WattsAmperes: measure of the rate of flow of electricity in a conductor. Watt/voltsVolts: measure of electrical pressure. Watt/amperesWatts: measure of the amount of energy or work that can be done. Volts x amperesOhms: measure of electrical resistance to flow
5 Ohm LawGeorge Simon Ohm –made several discovers relating to electrical current.Ohm law is the unit used to measure a material’s resistance to the flow of electrical current.
6 Ohm’s Law --- Formulas Ohm = R Volts = E Amps = I Ohm’s Law: E = IR I=E/RR=E/I
7 MeasurementsVoltage, amperage, and resistance can be measured by various types of meters.Voltmeter – measures voltageAmmeter – measures amperageOhmmeter – measures resistance
8 Electrical Safety Shock and Fire Never disconnect any safety device Don’t touch electrical items with wet hands or feetDon’t remove ground plug prongUse GFI in wet areasDiscontinue use of extension cord that feels warmDon’t put extension cords under carpet
9 Electrical Safety Install wiring according to NEC Blown fuse or breaker, determine causeDon’t replace fuse with larger fuseDon’t leave heat producing appliances unattendedHeaters & lamps away from combustiblesDon’t remove back of TV (30,000v when off)Electric motors lubricated, free of grease etc.
10 Electrical Safety Keep appliances dry Don’t use damaged switches, outlets, fixtures, extension cordsFollow manufacturer’s instructions (RTDM) for installation and use of electrical equipment
11 Power Generation & Distribution systems Power Plant to Step-up station(13,800 – 22,000 volts)Step-up station thru transmission lines (69,000 – 750,000 volts) to a Step-down station.Step-down station reduces to ,000 volts to home transformer.
12 Service EntranceTransformer: drops volts from 72,00-14,000 volts to 240 volts (three wires)Service drop: wires etc from transformer to houseEntrance head: weather-proof at houseMeter: $$$Service Entrance Panel (SEP): box with fuses or breakers
13 Electric Meter Kilowatthours: how electricity is sold Kilo = 1000 Watthour = use of 1 watt for one hour100 watt light bulb for 1 hour watthoursKilowatthour = 1000 watts for one hour
14 TermsAlternating current (AC) – Electrical current that alternates or changes direction several times per second. Current moves on the direction the voltage forces it.
15 TermsDirect Current (DC) – Electrical current flowing in one direction.Transformer – a device used to increase or decrease voltage.Cycle – The flow of electricity in one direction, the reverse flow of electricity in the other direction, and the start of flow in the other direction.
16 TermsSingle Phase – most common. One transformer is used between the distribution line and the meter. Has three wires, two “hot” and one neutral. Provides service for 120 volt and 240 volt systems.
17 TermsThree Phase – designed especially for large electrical loads. More expensive due to three wires and three transformers. Advantage is that the load is divided among the three phases and design for three-phase motors.
18 TermsShort circuit – direct connection between “hot” & neutral wires.
19 TermsFuse – a device used to protect circuits from an overload of current. Must be replaced.Circuit breaker – protects circuits. Can be manually reset for further use.Time-Delay fuse – a fuse having the ability to carry an overload of a short period before melting the fuse link.
20 TermsUnderwriters’ Laboratory (U.L.) – a national organization that tests all types of wiring materials and electrical devices to insure they meet minimum standards for safety and quality.
21 TermsNational Electrical Code (N.E.C.) regulates electrical wiring installations. Regulations are approved by the National Board of Fire Underwriters,
22 Branch Circuits usually begin at SEP branch out into a variety of placesonly 1 motor or;series of outlets or;series of lightsuse correct size wire and fuse or breaker
23 Types of CableNonmetallic sheathed cable: copper or aluminum wire covered with paper, rubber, or vinyl for insulationArmored cable: flexible metal sheath with individual wires inside. Wires are insulatedConduit: tubing with individually insulated wires
24 Wire Type and Size copper No 14 (14 gauge) = 15 amp circuits No 12 = 20 ampsNo 10 = 30 ampsaluminum use one size largerlower gauge number = larger wireNo 8 and larger use bundles of wirescurrent travels on outer surface of wire, so a bundle of smaller wires can carry more
25 Voltage Drop loss of voltage as it travels along a wire lights dim, motors overheatlarger wires have less voltage drop for a given amount of currentlonger wire = greater problemmust increase wire size as distance increases
26 Wire IdentificationType of outer covering, individual wire covering, cable construction, number of wiresWire type stamped on outer surface
27 Wire Types Type T – use in dry locations only Type TW – can used in dry or wet conditionTHHN – dry location with high tempsTHW and THWN - wet, high tempsXHHW - high moisture & heat resistanceUF - direct burial in soil but not concrete
28 Wire IdentificationColor coded: black, red, & blue = positive or hot wires which carry current to appliancesWhite = neutral wires carry current from appliance back to sourceGreen or Bare = ground all metal boxes and appliances
29 Wire IdentificationWire Size: 12-2 has two strands of No. 12 wire (black & white)12-2 w/g same, with one green or bare12-3 has three strands of No. 12 (black, red, white)12-3 w/g same, with green or bare