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AboutElectricity
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2
Subpart S - Electrical(1910.301 - 399)
515
457
396
347
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303(g)(2)(i)
305(b)(1)
304(f)(4)
305(b)(2)
305(g)(1)(iii)
Live parts
Grounding path
Electrical box covers
Conductors entering cabinets/boxes/fittings protected from abrasion
Standard:1910.
Use of flexible cords and cables
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*
*
*
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*Average number of Federal OSHA citations issued
between 2000 and 2003
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ELEMENTS & ATOMS
Every known substancesolid, liquid orgas is composed of elements
An atom is the smallest particle of anelement that retains all the propertiesof that element
Each element has its own kind of atom
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ATOMS
Inner part composed of protons & neutrons
Outer part composed of electrons
Protons = positive charge
Neutrons = no charge
Electrons = negative charge
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ATOMS
Each element has a definite number ofelectrons ----and the same number of
protons
They are oppositely charged andtherefore attract each other. This tendsto hold the electrons in orbit around theatom.
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ELECTRICALLY BALANCEDATOM
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FREE ELECTRONS
Some atoms are easily moved out of orbit
The ability to move or flow is the basis ofcurrent electricity
If channeled in a given direction, a flow ofelectrons occurs --- when flowed through aconductor it is dynamic electricity
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ELECTICAL MATERIALS
CONDUCTORcontains many free
electrons --- gold, copper, silver,aluminum
INSULATORcontains few freeelectrons-Usually non-metallic such aswood, rubber, glass, etc
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GENERATING ELECTRICITY
Friction, pressure, heat, light, chemicalreaction, and magnetism
Magnetism is most practical & inexpensivemethod
Electricity is produced when a magnet ismoved past a piece of wire, or wire is
moved through a magnetic field
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VOLTAGE, CURRENT, &RESISTANCE
VOLTAGEunit of measurement of electromotiveforce (EMF)
CURRENT - Continuous movement of electrons past agiven point. (measured in amperes)
RESISTANCEOpposition to movement of electrons.Makes it possible to generate heat, control current
flow, & supply correct voltage to devices
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OHMS LAW
George Simon Ohm
Formulated a mathematical relationship between:
Current
Voltage
Resistance
Resistance = Impedance
Resistance = DC
Impedance = AC
InterchangeableMost Branch circuits
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DIRECT CURRENT
Always flows in one direction
Used to charge batteries, run somemotors, operate magnetic lifting devicesand welding equipment.
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ALTERNATING CURRRENT
More common in electrical work
Changes rapidly in both direction andvalue
Power companies produce powercheaper with alternating current
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Arc Flash and Arc Blasts
Arc Flash:
80%-Burns due toignition of clothing
Temperature-35,000F
Fatal Burns-10 ft.
2000 peoplehospitalized withburns
Molten metal
Arc Blast:
Pressure Wave
Heat Molten metal
Destruction ofstructures and life
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ELECTRICAL HAZARDS
ARC-BLAST. The three primaryhazards associated with an arc-
blast are:Thermal radiation.
Pressure Wave.
Projectiles.
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ELECTRICAL HAZARDS
EXPLOSIONS. Explosions occurwhen electricity provides a source
of ignition for an explosive mixturein the atmosphere.
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ELECTRICAL HAZARDS
FIRES. Electricity is one of themost common causes of fires both
in the home and in the workplace.Defective or misused electricalequipment is a major cause.
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EFFECTS ON THEHUMAN BODY
Depends on:
Current and Voltage
Resistance
Path through body
Duration of shock
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Effects of AC Electricity
More than 3 mA- Painful shock- causeindirect accident
More than 10 mA- Muscle contractionNo Let Go danger
More than 30 mA- Lung paralysis,
usually temporary
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Effects of AC Electricity
More than 50 mA- Ventricularfibrillation, usually fatal
100 mA to 4 A- Certain ventricularfibrillation, fatal
Over 4 A- Heart paralysis, severe burns
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Effects
Protection
Circuit Breakers
Fuses 15 or 20 amps
Property/equipment protection
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Conductors
American Wire Gauge 12 gauge20 amps (Safely)
14 gauge15 amps 10 gauge30 amps
What determines amount of ampsthrough a circuit? How much the equipment draws
How much stuff plugged in
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Protective Devices
Fuses
Circuit Breakers
Trip or break circuit breakers if conductorsexceed their ampacity
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Summary
Current (I)
Voltage (E or v)
Resistance (R) (Ohms)
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Electrocution Triangle
Electricity (levels)
Time
Path
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Wires
Black = hot = Ungrounded Conductor
White = neutral = Grounded Conductor
(connected to groundingelectrode/Grounding rod)
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How to check
Wiring Checks
Testers
Different types
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Instruments
Normal 3 light Tester
Wont check resistance to ground
Others - Check what the 3 light testerwill
Also checks resistance for ground
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