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Chapter 3: Electrical Theory and Practice
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Transcript of Chapter 3: Electrical Theory and Practice
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Notes taken from Gillette’s Designing with Light
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Atoms are the smallest complete building block in nature Atoms are made up
of:Protons - positive
chargeElectrons - negative
chargeNeutrons - neutral
charge
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A stable atom # of electrons in
orbit around the nucleus = # of protons in the nucleus
Ie. Hyrdrogen
Electron
Nucleus
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Law of Charges Like charges repel and unlike charges attract
Two protons would defy attempts to be close togetherSame with electrons
An electron and proton would stick together
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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
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Electrical current The flow or movement of electrons through a
conductor
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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
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There are two types of electrical current: Direct current (DC)
The flow of electrons in one direction. AKA: Batteries
Short distances
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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
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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
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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
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Series
www.berkeleypoint.com/images/series.jpg
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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
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Parallel
www.berkeleypoint.com/images/series.jpg
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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.
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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
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Ohm’s Law I=current in amperes E=voltage in volts R=resistance in ohms
I=E/R E=IR R=E/I
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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
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Power Formula “PIE” P=power in watts I=current in amperes E=voltage in volts
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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
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Dimmer Voltage = 120VAC Dimmer can handle 20 amperes of
current What is the maximum safe load that can
be placed on this dimmer
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How many 575W instruments can you plug into a 2400W dimmer with cable that can carry 20 amperes of current?
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How many 750W instruments can you plug into a 2400W dimmer with cable that can carry 20 amperes of current?
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System Voltage = 120VAC 14 gauge cable connecting the
instruments can carry 15 amperes How many 500 watt instruments can be
loaded onto a dimmer?
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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
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Created when a large SURGE of current causes a portion of the conductor to explosively melt
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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
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Electrical cable containing hot, neutral and ground wires
Connects lighting instrument to the power source
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Plug Male portion of a connecting device
Receptacle Female portion of a connecting device
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Many hand tools do not have ground pins Instead they have an outer plastic
insulation that protects you from a short circuit
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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
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HOT = BLACK, occasionally RED GROUND = GREEN NEUTRAL = WHITE
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Greater current in system than it was designed to handle
Fuse and circuit breaker protects from overload Must have matching amperage as system
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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.jpgimages.orgill.com/200x200/4180923.jpg
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Circuit Breaker Like a switch Bimetal strip flexes to trip circuit if overloaded
cache.smarthome.com/images/7103.jpg
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1. If you don’t know what you are doing, don’t do it. Ask for help.
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2. Use tools covered with plastic or rubber insulation
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3. Use wooden or fiberglass ladders
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4. Disconnect device from circuit before you work on it.
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5. Use common senseDon’t touch bare wiresDon’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
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6. Maintain ground circuits
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7. Check cables and connectors periodically. Replace cracked, chipped or deteriorating equipment
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8. Keep cables and connectors clean.
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9. Store cables neatly with ends plugged together and tied
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10. Disconnect plug by pulling on body of plug.
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11. Ensure all elements have same electrical rating.