Chapter 3: Electrical Theory and Practice

1. Chapter 3: Electrical Theory and Practice Notes taken from Gillette’s Designing with Light

2. Atomic Structure • Atoms are the smallest complete building block in nature • Atoms are made up of: • Protons - positive charge • Electrons - negative charge • Neutrons - neutral charge

3. Atomic Structure • A stable atom • # of electrons in orbit around the nucleus = # of protons in the nucleus • Ie. Hyrdrogen Electron Nucleus

4. Atomic Structure • Law of Charges • Like charges repel and unlike charges attract • Two protons would defy attempts to be close together • Same with electrons • An electron and proton would stick together

5. Atomic Structure • Valence shell: the outermost plane of orbiting electrons in the structure of an atom • Weak force holds electron in orbit • Free electrons: an electron that has broken away from its “home” atom to float free • Copper

6. Atomic Structure • Electrical current • The flow or movement of electrons through a conductor

7. Atomic Structure • Ampere: the unit of measurement of electrical current • Potential: the difference in electrical charge between two bodies; measured in volts • Volt: the unit of measurement of electrical potential

8. Electricity at work • There are two types of electrical current: • Direct current (DC) • The flow of electrons in one direction. AKA: Batteries • Short distances

9. Electricity at work • There are two types of electrical current: • Alternating current (AC) • Transmitted over long distances • The flow of electrons is reversed on a periodic basis. • Utility companies http://www.answers.com/topic/alternating-current

10. Basic Circuits • 3 parts • Source: the origin of electrical potential • battery or 120-volt wall outlet • Load: a device that converts electrical energy into another form of energy • Lamp or motor • Circuit: a conductive path through which electricity flows • Wire or cable

11. Basic Circuits Series • In a series circuit all of the electricity flows through every element of the circuit • If any of the loads don’t work then the circuit will be broken, the electricity won’t flow, and the remaining loads won’t work either

12. Basic Circuits Series www.berkeleypoint.com/images/series.jpg

13. Basic Circuits Parallel • In a parallel circuit only a portion of the electricity flows through each of the branches of the circuit • If one load on a circuit doesn’t work then the electricity will continue to flow in the rest of the circuit and the other loads will continue to work

14. Basic Circuits Parallel www.berkeleypoint.com/images/series.jpg

15. Basic Circuits The Combination Circuit • Combines the principles of the two primary circuits. • Any electrical circuit that uses a switch to control a load is an example of a combination circuit.

16. Power Calculations • Ohm’s Law • As voltage increases, current increases; as resistance increases, current decreases • Resistance • Opposition to electron flow within a conductor • Depends on chemical makeup • Measured in Ohm’s • Low-voltage systems

17. Power Calculations • Ohm’s Law • I=current in amperes • E=voltage in volts • R=resistance in ohms • I=E/R • E=IR • R=E/I

18. Power Calculations • Power Formula • Higher voltage • Watts • Unit of measurement of power required to do work • Amount of electrical energy converted or consumed • Converted into light, heat or mechanical energy

19. Power Calculations • Power Formula • “PIE” • P=power in watts • I=current in amperes • E=voltage in volts

20. Power Calculations • Power Formula • “PIE” • P=power in watts • I=current in amperes • E=voltage in volts • P=IE • West Virginia • W=power in watts • V=voltage in volts • A=current in amperes • W=VA

21. Problem #1 • Dimmer Voltage = 120VAC • Dimmer can handle 20 amperes of current • What is the maximum safe load that can be placed on this dimmer

22. Problem 1a • How many 575W instruments can you plug into a 2400W dimmer with cable that can carry 20 amperes of current?

23. Problem 1b • How many 750W instruments can you plug into a 2400W dimmer with cable that can carry 20 amperes of current?

24. Problem #2 • System Voltage = 120VAC • 14 gauge cable connecting the instruments can carry 15 amperes • How many 500 watt instruments can be loaded onto a dimmer?

25. Conductors and Insulators • Conductor • Any material with an abundance of free electrons • Water, copper, silver, gold, aluminum • Insulator • Any material with few free electrons • Air, glass, paper, rubber, most plastics

26. Short Circuit • Created when a large SURGE of current causes a portion of the conductor to explosively melt

27. Grounding • Provides a low resistance path for the electricity to follow in case of a short circuit between the hot wire and the devices metallic housing http://sol.sci.uop.edu/~jfalward/physics17/chapter8/plugwithground.jpg

28. Pigtail • Electrical cable containing hot, neutral and ground wires • Connects lighting instrument to the power source

29. Pigtail • Plug • Male portion of a connecting device • Receptacle • Female portion of a connecting device

30. Double Insulation • Many hand tools do not have ground pins • Instead they have an outer plastic insulation that protects you from a short circuit

31. System Ground • The grounding point • Usually a metal rod driven into the ground or an underground metal water pipe http://en.wikipedia.org/wiki/Image:HomeEarthRodAustralia1.jpg

32. Wiring • HOT = BLACK, occasionally RED • GROUND = GREEN • NEUTRAL = WHITE

33. Overload • Greater current in system than it was designed to handle • Fuse and circuit breaker protects from overload • Must have matching amperage as system

34. Overload • Fuse • Contains a soft metallic strip that melts when the current exceeds what the system is designed for • Must be replaced when “blown” http://www.m-99.co.uk/Car_Audio/Car_Fuses/gold_fuse.jpg images/jpegs/fuse30a.jpg images.orgill.com/200x200/4180923.jpg

35. Overload • Circuit Breaker • Like a switch • Bimetal strip flexes to trip circuit if overloaded cache.smarthome.com/images/7103.jpg

36. Electrical Hazards • 1. If you don’t know what you are doing, don’t do it. Ask for help.

37. Electrical Hazards • 2. Use tools covered with plastic or rubber insulation

38. Electrical Hazards • 3. Use wooden or fiberglass ladders

39. Electrical Hazards • 4. Disconnect device from circuit before you work on it.

40. Electrical Hazards • 5. Use common sense • Don’t touch bare wires • Don’t work in damp locations or put drink where it could spill • Don’t intentionally overload circuit • Don’t try to bypass fuse or circuit breaker

41. Electrical Hazards • 6. Maintain ground circuits

42. Electrical Hazards • 7. Check cables and connectors periodically. Replace cracked, chipped or deteriorating equipment

43. Electrical Hazards • 8. Keep cables and connectors clean.

44. Electrical Hazards • 9. Store cables neatly with ends plugged together and tied

45. Electrical Hazards • 10. Disconnect plug by pulling on body of plug.

46. Electrical Hazards • 11. Ensure all elements have same electrical rating.