AbouT Electricty

8/11/2019 AbouT Electricty

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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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*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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