Home Ele Safety

8/12/2019 Home Ele Safety

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Subpart S - Electrical(1910.301 - 399)

515

457

396

347

290

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

*

*

*

*

*

*Average number of Federal OSHA citations issued

between 2000 and 2003


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DEFINITION

A physical agency caused by the motion

of electrons, protons, and othercharged particles, manifesting itself asan attraction, repulsion, magnetic,

luminous, and heating effects, etc.


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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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ELECTRICAL HAZARDS

SHOCK. Electric shock occurs whenthe human body becomes part ofthe path through which current

flows.The direct result can beelectrocution.

The indirect result can be injuryresulting from a fall or movementinto machinery because of a shock


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ELECTRICAL HAZARDS

BURNS. Burns can result when aperson touches electrical wiring orequipment that is energized.

ARC-BLAST. Arc-blasts occur fromhigh- amperage currents arcing

through the air. This can be caused byaccidental contact with energizedcomponents or equipment failure.


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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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Arc Blast

Cause

Short Circuit caused by working on

energized equipmentDropped Tool

Occurs in milliseconds

Temp: 30,000 degrees

Air expands very violently

15 tons of pressure


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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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Double Insulated

Indicators

No ground pin

Plastic tool case Listed by NTL

Marked as double insulated

Square in a squareMarked double insulated

l i l


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1910.302 ElectricalUtilization Systems

Scope:

(a) Covers electrical installations and

utilization equipment installed or used within

or on buildings, structures, and other

premises

1910 303 General


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(a) Approval. The conductors and equipment

required or permitted by this subpart shall be

acceptable only if approved

1910.303 GeneralRequirements

1910.303(a) ApprovalAll electrical conductors and equipment

shall be approved.

UNDERWRITERS

LABORATORIES

ENCLOSED SWITCH

Issue AK 3225

LISTED

1910.303(a)

NEC Article 110-2

1910 303 (b) Examination


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1910.303 (b) Examination,installation and use

Emp loyer Obl igation:

(1) Electrical equipment shall be free from

recognized hazards that are likely to cause

death or serious physical harm to employees

1910 303 (b) Examination


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(1) Examination. Safety of equipment shalldetermined using the following

considerations:

(i) Suitability of equipmentfor an identified

purpose may be evidenced by listing or labeling for

that identified purpose

1910.303 (b) Examination,installation, and use


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1910.303 (f) ID of

Disconnecting MeansEach service, feeder, and branch circuit, at itsovercurrent device, legibly and durably marked

to indicate its purposeSwitches and circuit breakers must be clearly

labeled to indicate its circuits function

Circuit breaker for motors

1,2,3, and 4


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1910.303(g) WorkingSpace

(1) Sufficient access and working space around

all electrical equipment, provided & maintained

to provide ready and safe operation and

maintenance

(ii) Not used

for storage

(ii) If located in aisle or general open area,

working space shall be suitably guarded

1910 303(g)(1)(v)


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1910.303(g)(1)(v)Illumination

Illumination provided for

all working spaces about

service equipment,

switchboards, panel-

boards, and motor controlcenters installed indoors.

1910 303(g)(1)(vi)


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1910.303(g)(1)(vi)Headroom

The minimum

headroom of working

spaces about service

equipment,

switchboards, panel-

boards, or motorcontrol centers shall

be 6 feet 3 inches

6'3"


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G di li t 1910 303


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(g)(2)(i) or other forms of approved enclosures,

or by any of the following means: (A) By location in a room, vault, accessible only to

qualified persons

(B) By permanent, substantial partitions or screens

(C) By location on a suitable

balcony or platform as to exclude

unqualified persons

(D) By elevation of 8 feet or more

above the floor or other

working surface

Guarding live parts 1910.303

1910 303(g) G a ding li e pa ts


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1910. 303(g) Guarding live parts

(2)(iii) Entrances to rooms

and other guarded locations

containing exposed live

parts shall be marked with

conspicuous warning signs

forbidding unqualified

persons to enter


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1910.303(h)(3)(ii) Illumination

Adequate illumination for allworking spaces about

electric equipment

The lighting outlets arrangedthat persons changing lamps

or making repairs on the

lighting system will not be

endangered by live parts or

other equipment


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1910 304( )(1) Id tifi ti f


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1910.304(a)(1) Identification ofConductors

A conductor used as a

grounded conductor shall be

identifiable and distinguishable

from all other conductors.

A conductor used as an

equipment grounding conductorshall be identifiable and

distinguishable from all other

conductors


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Identification of ConductorsGrounded conductor and equipment grounding

conductors marked or color coatedSo that employees can i.d. and tell apart

Grounded conductor is an energized circuit

(conductor that is connected to earth through

the system ground) Commonly referred to as

the neutral

G di C d


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Grounding Conductors

Equipment grounding conductoracts as a

safeguard against insulation failure or faults in

the other circuit conductors

Not an energized conductorunder normalconditions.

Energized if a leak or fault in the normal

current pathDirects current back to the source

Enabling fuses or circuit breakers to operate


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Identification of Conductors

Grounded conductori.d. and distinguished

from other conductors w/ white or gray

Equipment grounding conductori.d. and

distinguished w/ green, green w/ yellow stripes,

or bare


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1910.304(a) Use and identification ofgrounded and grounding conductors

(2) No grounded conductor may be attached to

any terminal or lead so as to reverse polarity

(3) A grounding terminal on a receptacle, cord

connector, or plug may not be used for

purposes other than grounding

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