Cooper Bussmann Safety Basics Electrical Hazards

5/25/2018 Cooper Bussmann Safety Basics Electrical Hazards

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SafetyBASICsTM

2004 Cooper Bussmann2004 Cooper Bussmann

BussmannAwarenessof Safety IssuesCampaign

Electrical Hazards


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Electrical Hazards

What are the hazards as you approach

electrical equipment to perform work?



Electrical Hazards

Shock

Arc flash Heat

Fire

Arc blast Pressure

Shrapnel Sound

Example of an arcing fault



I = V / Z

What happens with shock?

What happens when there is a fault?

What is the difference between a short-circuit and an arcing fault?

Basic Electrical Theory



Electric Shock

Over 30,000 non-fatal electrical shock

accidents occur each year

Over 600 people die from electrocutioneach year

Electrocution remains the fourth (4th)

highest cause of industrial fatalities Most injuries and deaths could be

avoided



Human Resistance Values

Resistance (ohms)

Condition Dry Wet

Finger touch 40,000 to 1,000,000 4,000 to 15,000

Hand holding wire 15,000 to 50,000 3,000 to 6,000

Finger-thumb grasp 10,000 to 30,000 2,000 to 5,000

Hand holding pliers 5,000 to 10,000 1,000 to 3,000

Palm touch 3,000 to 8,000 1,000 to 2,000

Hand around 1-1/2 inch pipe 1,000 to 3,000 500 to 1,500

Two hands around 1-1/2 inch pipe 500 to 1,500 250 to 750

Hand immersed 200 to 500Foot immersed 100 to 300

Human body, internal, excluding

skin

200 to 1,000

This table was compiled from data developed by Kouwenhoven and Milnor.



Electric Shock

Human body resistance (hand to hand)across the body is about 1000 W

Ohms law: I = V / R amps= 480 volts / 1000 W= 0.48 amps (480 mA)

Product safety standardsconsider 5 mAto be the safe upper limit for childrenand adults



Electric Shock

mA Affect on person

0.5 - 3 - Tingling sensations

3 - 10 - Muscle contractions and pain10 - 40 - Let-go threshold

30 - 75 - Respiratory paralysis

100 - 200 - Ventricular fibrillation200 - 500 - Heart clamps tight

1500 + - Tissue and organs start to burn



Electric Current Pathways

(A) Touch Potential (B) Step Potential (C and D) Touch / Step PotentialCurrent pass ing thro ugh the hear t and lungs is the most ser ious



Electric Shock Injury



Arc Flash

As much as 80% of all electrical injuries are

burnsresulting from an arc-flash and ignition

of flammable clothing

Arc temperature can reach 35,000F - this is

four times hotter than the surface of the sun

Fatal burns can occur at distances over 10 ft

Over 2000 people are admitted into burn

centers each year with severe electrical burns



Arc Blast

An arc fault develops a pressure wave

Sources of this blast include:

Copper expands 67,000 timesits original volume

when vaporized Heat from the arc, causes air to expand, in the

same way that thunder is created from a lightningstrike

This may result in a violent explosion of circuitcomponents and thrown shrapnel

The blast can destroy structures, knock workersfrom ladders, or across the room


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BoltedShort Circuit

A B

ArcingFault

A B

Current

Thru Air


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Electric Arc

Copper Vapor:Solid to Vapor

Expands by67,000 times

Intense Light

Hot Air-Rapid Expansion

35,000 F

Pressure Waves

Sound Waves

Molten Metal

Shrapnel


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Personnel Hazards Associated

With Arc Flash & Arc Blast

Heatburns & ignition of material

Arc temperature of 35,000oF

Molten metal, copper vapor, heated air

Second degree burn threshold:

80oC / 175

oF (0.1 sec), 2nddegree burn

Third degree burn threshold:

96oC / 205oF (0.1 sec), 3rddegree burn

Intense light

Eye damage, cataracts


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Pressures from expansion of metals &air

Eardrum rupture threshold:

720 lbs/ft2

Lung damage threshold:

1728 - 2160 lbs/ft2

Shrapnel

Flung across room or fromladder/bucket

Personnel Hazards Associated

With Arc Flash & Arc Blast


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Flash protection boundaries and

incident energy exposure calculations

both dependent upon:

Duration of arc-fault or time to clear Speed of the overcurrent protective

device

Arc-fault current magnitude

Available fault current

Current-limitation can reduce

Overcurrent Protection Role


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IEEE / PCIC & NFPA 70E

Ad Hoc Safety Subcommittee

Users

Consultants

Manufacturers

Medical experts

Following are some of the tests runAll of the devices used for this testing were

applied according to their listed ratings


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IEEE / PCIC Staged Arc Flash Test

Set-up


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22.6 KA Symmetrical

Available Fault Current

@ 480V, 3 Phase

Fault Initiated on

Line Side of 30A

Fuse

30A RK-1

Current Limiting Fuse

Size 1 Starter

Test No. 46 cycle STD640A OCPD

Non Current Limiting

with Short Time Delay

Set @ 6 cycle opening


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Test 4 Still Photo


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Test 4 Still Photo


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Test 4 Still Photo


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Test 4 Still Photo


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Test 4 Still Photo


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Test 4 Still Photo


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Test 4 Still Photo


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>225oC/437

oF

>225oC/

437oF

Results: Test No.4

T1T2

P1

T3

Sound141.5 db @ 2 ft.

50oC/122

oF

>2160 lbs/ft2

> Indicates Meter Pegged


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22.6 KA Symmetrical


@ 480V, 3 Phase

Fault Initiated on

Line Side of 30A

Fuse30A RK-1


Size 1 Starter

Test No. 3601A.

Class L



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Test 3 Still Photo


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Test 3 Still Photo


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Test 3 Still Photo


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Test 3 Still Photo


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> 175

o

C/347oF

Results: Test No.3

T1

T2

P1

Sound

133 db @ 2 ft.

62oC/143.6

oF

504 lbs/ft2

T3(No Change

From Ambient)

> Indicates Meter Pegged


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22.6 KA Symmetrical


@ 480V, 3 Phase

30A RK-1

Current Limiting

Fuse

Size 1 Starter

Test No. 1601A.

Class L

Current Limiting

Fuse

Fault Initiated on

Load Side of 30A

Fuse


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Test 1 Still Photo


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Test 1 Still Photo


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Test 1 Still Photo


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Test 1 Still Photo


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Results: Test No.1

T1

T2

P1

T3

Sound

(No Change

From Ambient)

(No Change

From Ambient)

(No Change

From Ambient)

(No ChangeFrom Ambient)

(No Change

From Ambient)


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Non-Current Limiting

Reduced Fault Current

via Current-Limitation

Test 1

Test 4

Test 3

Current-Limitation: Arc Energy

Reduction


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Summary

Shock, arc flash and arc blast are the

three recognized electrical hazards

Shock injuries result from electrical

current flowing through the bodyArcing faults can generate enormous

amounts of energy

Injuries from arcing faults are a result ofthe tremendous heat and pressure

generated


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Summary

Overcurrent protective devices have an

impact on the two most important

variables of arc flash hazards: Time (speed of the OCPD) Fault current magnitude (current-limitation

may help reduce)

Current-limitation may be able tosignificantly reduce the energy released

during arcing faults

Cooper Bussmann Safety Basics Electrical Hazards

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