1. Ag Eng I Electricity Unit E

2. Electricity Q. Who invented electricity? A. No one, it is based on laws of physics Benjamin Franklin is created with the discovery of electricity. He proved his theory by flying a kite in a thunder storm. Benjamin Franklin is created with the discovery of electricity. He proved his theory by flying a kite in a thunder storm.

3. Electricity It took almost one hundred years from the time of the discovery of electricity until the first electrical machine or invention was produced. Can you guess what it was? Light Bulb Light Bulb

4. Electricity Where does our electricity come from that we use at our home? In eastern NC its Progress Energy. They produce electricity for a profit just like any other business.

5. Electricity In rural communities, electric membership co-ops were formed to provide electricity to the places that the for profit companies would not go. In our school district that co-op is Four County Electric.

6. Sources of Power Power is produced by a generator. The generator is driven by some type of external power. The common sources of external power are: Fossil Fuels NuclearHydro-ElectricSolar

7. Sources of Power In our area we have power produced by Coal burning plants in Wilmington Nuclear plants at Shearon Harris and South Port.

8. If you don’t see it on your handout, then write it in. It was added because it was important.

9. Electrical Principles and Wiring Materials

10. 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: electricity flows easily n Insulator: material that provides great resistance

11. 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; electrical power n Watts = Volts x Amps n W =VA West Virginia formula

12. Ohm’s Law n Ohm: measure of electrical resistance to flow n Resistance = R n Volts = E n Amps = I n Ohm’s Law: E = IR I=E/RR=E/I

13. Electrical Safety n Two hazards: 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

14. 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 Keep heaters & lamps away from combustibles n Don’t remove back of TV (30,000v when off)

15. Electrical Safety n Keep appliances dry n Don’t use damaged switches, outlets, fixtures, extension cords n Do not remove the long ground prong from 120v three-prong plugs n Follow manufacturer’s instructions for installation and use of electrical equipment

16. Service Entrance n Power comes from power company n Transformer: drops volts from 25,000 volts to 240 volts n Service drop: wires that carry electricity from transformer to house n Entrance head: weather-proof at house n Meter: measure in kw hrs = $$$ n Service Entrance Panel (SEP): box with fuses or breakers

17. 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 - 100 watthours n Kilowatthour = 1000 watts for one hour

18. 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

19. 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

20. Wire Type and Size n Wire size is measured by gauges n No 14 (14 gauge) = 15 amp circuits n No 12 = 20 amps n No 10 = 30 amps n Copper is better conductor than aluminum n aluminum uses one size larger than copper 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

21. Voltage Drop n loss of voltage as it travels along a wire n Causes lights to 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

22. Wire Identification n Type of outer covering, individual wire covering, cable construction, and number of wires determines where cable can be used n Wire type stamped on outer surface

23. Wire Types n Type T - dry locations n Type TW - dry or wet n RHW – is rubber, heat + moisture resistant 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 SE/SEU – unarmored service entrance cabl n ASE – armored service entrance cable n USE – Underground service entrance

24. 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

25. 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

26. Definitions n Circuit Breaker – protects circuits from overload of current by tripping to break or open the circuit n Fuse – protects circuits from overload by melting a metal strip in the fuse

27. Three way switching system

28. Four way switching system

29. Def. n Hot wire – current carrying conductor under electrical pressure n Neutral wire – current carrying conductor not under pressure n Ground wire – conducting wire that transmits current to the earth to minimize the danger of electrical shock

30. Computing Electrical Costs n Watts = Volts x Amps n How many watts of electricity will a 7.5 amp motor use in 5 hrs on a 120 Volt circuit? n W = 120 x 7.5 n = 900 x 5 hrs n W = 4500 n How many kilowatts is this? n 4500/1000 = 4.5 kw

31. Calculating Volts n Volts equal watts divided by amps n V = W / A n What volt circuit is needed for a 7.5 amp electric motor that uses 900 watts in one hour? n V = 900 / 7.5 n V = 120

32. Calculating Amps n Amps = Watts / Volts n What should the amp rating of an electric motor be if it uses 1500 watts of electricity in 1 hour in a 120v circuit? n A = 1500 / 120 n A = 12.5

33. Cost of Electricty n $ = cost per kW x # of kw x hours use n Note: kilowatt is 1000 watts n If electricity costs $.12/kwh, how much would it cost to use 2 kw per hour for 10 hours? n = $.12 x 2 kw x 10 hr n = $2.40

34. Switches n Single pole- 2 terminals, one location n Threeway – 3 terminals, two locations n Fourway – four terminals and is used in combination with three way switches to control lights from three or more locations

35. Proper Wire Sizing and Protection of the Circuit

36. Fuse A one time use device that protects the circuit from overloading. If the circuit is overloaded the fuse will “blow” (the filament in the fuse will melt in two) The size of fuse used will depend on the size of wire that is being used in the circuit

37. Circuit Breaker Device that is used to keep the circuit from becoming overloaded. Overloaded circuits become hot and can catch fire. Will “trip” if overloaded The size of breaker depends on the size wire that is being used on the circuit.

38. Wire Size and Breaker Size Wire SizeBreaker Size 1415 1220 1030 840 840 655 655

39. Wire sizes AWG = American Wire Gauge – a standard for designating the size of electrical wire The larger the number, the smaller the diameter of the wire. The smaller number, the larger the diameter of the wire

40. House Wiring Most circuits in houses are either size 14 or 12. Larger appliances such as dryers and ranges use larger wire (10 or 8)

41. Wire Size Labeling NEC state that all electrical conductors have the following info stamped on the wire AWG Size Voltage Rating Insulation TypeTesting Agency Number of Conductors

42. Example of Commmon Wires n 12/2 n 12/2 wg n 12/3 wg n 14/2 n 12/2 wg n 14/3 wg

43. Single pole switch and light

44. Receptacle is always hot

45. Two threeway switches with light at end of run

46. Three way circuit with light at beginning of run

47. Three way switch with light in middle

48. Four way circuit with light at end

49. Always remember that electricity can kill you. Be certain all power is off before attempting to work with any electrical devices. Safety first.