K3L Bab#7 Electrical Safety

7/27/2019 K3L Bab#7 Electrical Safety

1/12

1

7BabBab

Electrical Safety

Outline of talk

2

Electrical Terminology

How does electricity work?

Electrical quantity

Working with electricity

Electrical safety devices

Reference :

Charles A. Wentz, Safety, Health and Environmental Protection, MGH, 1998.

Electrical Terminology Electricity: Negatively Charged Particles Moving Over

A Conductor

Current: Movement Of Electrons Along A Conductor

V = IR , V :voltage(V), I: current(A)

R : resistance ()

R = L/A , : resistivity(m), L: conductor

length (m),A: cross-sectional area (m2)

3

FluidsFluids ElectricityElectricity

PressurePressure VoltageVoltage

FlowFlow CurrentCurrent

FrictionFriction ResistanceResistance


2/12

2

Ground Or Grounding: The Draining Or Passage Of

Electricity Into The Earth

Alternating Current: Current That Alternates

Direction Through A Conductor

Direct Current: Current That Flows In The Same

Direction Through A Conductor

Static Electricity: Electrical Charge Resulting From

Friction Between Two Objects Or From Objects

Striking

4

Shock: Condition When The Body Becomes

A Part Of A Circuit

Polarity: The Flow Of Electrons In The

Proper Direction (From The Source To The

Device Or Negative To The Positive ThroughA Device

5

HOW DOES ELECTRICITY WORK?

Like Charges Attract; Unlike Charges Repel

Electricity: Negatively Charged Particles

(Electrons) Moving Over A Conductor

Conductor: A Material With A Relatively Low

Resistance To The Flow Of Electrons

Insulator: Material That Has A High Resistance

To The Flow Of Electrons

6


3/12

3

Electrical Quantities

Volts: A Measurement Of Electrical Pressure

Watts: A Unit Of Electrical Power

Amperes: A Measurement Of The Volume Of

Electrical Current

Ohms: Measure Of The Resistance To The Flow

Of Electrons

7

8

WORKING WITH

ELECTRICITY

REQUIRES GOOD

SAFETY HABITS

ELECTRICITY SAFETYWORK PRACTICES

Know Where The Hazards Are

Properly Maintain Equipment

No Exposed Parts Or Energized Surfaces

Use Barriers And Devices Where Appropriate

No Conductors To Walk On Or Trip On

No Jewelry, Or Other Metal Objects AroundElectricity

9


4/12

4

ELECTRICAL SAFETY

DEVICES

Insulation

Ground Fault Circuit Interrupters (GFCIs)

Double-Insulated Devices

Grounding (Circuit And Equipment)

Guarding

Fuses And Circuit Breakers

Personal Protective Equipment

10

Testing is required Because

Accidents are Unacceptable

11

No one should be injured because

We did not follow the rules.

ELECTRICITY SAFETY

EQUIPMENT TEST

12

T h e r e a r e t w o s e t s o f t e s t s :

T h e r e a r e t w o s e t s o f t e s t s : T h e r e a r e t w o s e t s o f t e s t s :

T h e r e a r e t w o s e t s o f t e s t s :

* D C l e a k a g e : * D C l e a k a g e : * D C l e a k a g e : * D C l e a k a g e :

U s e a m u l t i - m e t e r o n t h e h i g h e s t o h m s

r a n g e t o m e a s u r e t h e r e s i s t a n c e b e t w e e n t h e H o t / N e u t r a l

p r o n g s o f t h e w a l l p l u g ( s h o r t e d t o g e t h e r a n d w i t h t h e p o w e r

s w i t c h o n w h e r e o n e e x i s t s ) t o A L L e x p o s e d m e t a l p a r t s o f

t h e e q u i p m e n t i n c l u d i n g m e t a l l i c t r i m , k n o b s , c o n n e c t o r

s h e l l s a n d s h i e l d s , V H F a n d U H F a n t e n n a c o n n e c t i o n s , e t c .

T h i s r e s i s t a n c e m u s t n o t b e l e s s t h a n 1 M o h m .

T h i s r e s i s t a n c e m u s t n o t b e l e s s t h a n 1 M o h m .T h i s r e s i s t a n c e m u s t n o t b e l e s s t h a n 1 M o h m .

T h i s r e s i s t a n c e m u s t n o t b e l e s s t h a n 1 M o h m .


5/12

5

13

* A C l e a k a g e :

* A C l e a k a g e : * A C l e a k a g e :

* A C l e a k a g e :

C o n n e c t a 1 . 5 K o h m , 1 0 W a t t r e s i s t o r i n p a r a l l e l

w i t h a 0 . 1 5 u F , 1 5 0 V c a p a c i t o r .

W i t h y o u r m u l t i - m e t e r s e t o n A C V a c r o s s t h i s

c o m b i n a t i o n a n d t h e e q u i p m e n t p o w e r e d u p , t o u c h

b e t w e e n a k n o w n e a r t h g r o u n d a n d e a c h e x p o s e d m e t a l

p a r t o f t h e e q u i p m e n t a s a b o v e .

W A R N I N G : T a k e c a r e n o t t o t o u c h a n y t h i n g u n t i l y o u

h a v e c o n f i r m e d t h a t t h e l e a k a g e i s a c c e p t a b l e - y o u

c o u l d h a v e a s h o c k i n g e x p e r i e n c e !

T h e p o t e n t i a l m e a s u r e d f o r a n y e x p o s e d m e t a l s u r f a c e m u s t n o t

T h e p o t e n t i a l m e a s u r e d f o r a n y e x p o s e d m e t a l s u r f a c e m u s t n o t T h e p o t e n t i a l m e a s u r e d f o r a n y e x p o s e d m e t a l s u r f a c e m u s t n o t

T h e p o t e n t i a l m e a s u r e d f o r a n y e x p o s e d m e t a l s u r f a c e m u s t n o t

e x c e e d 0 . 7 5 V .

e x c e e d 0 . 7 5 V .e x c e e d 0 . 7 5 V .

e x c e e d 0 . 7 5 V .

Values Exceeded

14

If the equipment fails either of theseIf the equipment fails either of theseIf the equipment fails either of theseIf the equipment fails either of these

tests,tests,tests,tests,

The fault MUST be found andThe fault MUST be found andThe fault MUST be found andThe fault MUST be found and

corrected before putting it back incorrected before putting it back incorrected before putting it back incorrected before putting it back in

serviceserviceserviceservice

(Even if you are doing this for your in(Even if you are doing this for your in(Even if you are doing this for your in(Even if you are doing this for your in----

laws!).laws!).laws!).laws!).

WORKING SAFELY WITH CORDS

Inspect Cords Before Each Use

Be Sure Plug And Receptacle Have Proper

Mating Configuration

To Unplug, Never Pull On The Cord, Pull On

The Plug

Dont Use Nails, Staples, Screws, Etc, To Attach

Or Fasten A Cord Or Plug

15


6/12

6


Two Conductor Cords Are Illegal Damaged Cords Should Never Be Used

Ensure Enough Slack To Prevent Strain On

Plug Or Receptacle

A Plug-Receptacle Should Have At Least 8

Ounces Of Contact Tension

16


Cords Should Be Kept Clean And Free Of Kinks

And Insulation Breaks

Cords Crossing Vehicular Or Personnel

Passageways Should Be Protected, Sign

Posted, And Used Temporarily Or In An

Emergency

Cords Should Be Of Continuous Length And

Without Splices

17

What can be the result of unsafe

electrical practices?

18


7/12

7

UNSAFE ELECTRICAL PRACTICES CAN

CAUSE:

SHOCK

FIBRILATION

FIRE

DEATH

INCONVIENCE

19

ELECTRICAL CURRENT EFFECTS ON THE

HUMAN BODY

20

Current (mA) Effect on humans

3000

700

10070

50

30

20107

3

1

Heart stops

Major burns to body tissue

Burns to body tissue

Ventricular fibrillation of the heartRisk of death

Severe breathing

Severe shock

Difficult breathingMuscle contractionsPainful electrical shock

Mild shock

Threshold of sensation

ELECTRICAL SHOCK EFFECTS BASED ON THETYPE OF CURRENT

21

Shock effects 60 Hz AC (mA) DC (mA)

Threshold of sensation

Threshold of muscle decontrolLife threatening from heart and respiration failureThreshold of heart fibrillation

1

6-925100

5

7080

100


8/12

8

WHAT CAUSES SHOCKS?

Touching Both Wires Of An Electrical Circuit

Touching One Energized Wire And A GroundConductor

Touching The Case Of A Faulted Or Short

Circuited Appliance Or Machine

22

PRINCIPAL SOURCES OF ELECTRICAL SHOCK

23

A bare, live, energized conductor

A poorly insulated, live energized conductor

Failure of electrical equipment

Discharge of static electricity

Lightning strike

HOW IS THE SERIOUSNESS OF AN ELECTRICALSHOCK DETERMINED?

The Voltage (Pressure) On Circuit

Skin Resistance And Internal Resistance

Amount Of Current Flowing Through The

Body, A Function Of Volts And Amps

Path The Current Takes

Bodys Reaction To The Shock

Length Of Time Electricity Is Applied

24


9/12

9

ELECTRICAL RESISTANCE OF THE BODY

25

Part of body Resistance ()

Dry skin

Dry finger of each hand on two electrodes

Moist finger of each hand on two electrodes

Wet (salt solution) finger of each hand on two electrodes

Tight grip of both dry hand on two electrodesWet skin

Tight grip of both Wet (salt solution) hand on two electrodes

Internal body from hand to foot

Internal body from ear to ear

100,600-600,000

100,000

40,000

16,000

1,2001,000

700

400-600

100

EFFECTS OF ELECTRICAL SHOCK

Volts Divided By Resistance in Ohms = Current In Amps

120 Volts Divided By 100,000 Ohms = 0.0012 Amps Or1.2 Milliamps

1.2 Milliamps Is Perception Threshold

10-20 Milliamps Is Painful; Let-Go Threshold; Can Kill In

Time 100 Milliamps Can Kill In A Second; Cant Let Go

200 Milliamps Kills; Causes Heart Fibrillation; BurnsHuman Flesh

26

IF ELECTROCUTION OCCURS

DO NOT Touch The Victim Or The Conductor

Shut Off The Current At The Control Box

If Shutoff Not Immediately Available, Use Non-

Conducting Material To Free Victim

Call For Help

If Necessary And You Know How, Begin CPR

In Dealing With Electricity, Never Exceed Your

Expertise

27


10/12

10

28

Fibrillation and resuscitation

Fibrillation is the fine, rapid, erratic, movements that replace the normal

contraction, as seen at left, of the vetricular muscle of the heart

Fibrillation can be stopped by application of another controlledelectrical

shock, known as defibrillation, often seen in movies and on TV...

A stopped heart can often be resuscitated with CPR

techniques (cardiopulmonary resuscitation),

but seldom a fibrillating heart.

29

Electrical shorts can cause Fires

30

Letter-shaped symbol markingsare also used to indicateextinguisher suitability accordingto class of fire.

Extinguishers suitable for Class Afires should be identified by atriangle containing the letter "A."If colored, the triangle should be

green.


11/12

11

31

CURRENT

KILLS

(not voltage)

Current effects on human body, current through chest

(A, amps)

0.20 no fibrillation, but severe burning, no breathing

32

Effects of different current levels

through human body

Current passing through victim is determined by resistance.

Dry skin resistance is typically ~500,000 ohms.

Wet skin resistance falls to ~1000 ohms.

Internal resistance of body is only 100 to 500 ohms.

Most household electrical injuries occur in the bathroom as a

consequence.Our skin, when dry, normally protects us from electrocution if we make

inadvertent contact with 115V household voltages. Not so when wet...

33

Anything That has Energy (Electrical or

Kinetic) has the Potential To be a safety

hazard.

REMINDER!


12/12

BEST ADVICE

Treat Electricity With

The Respect It Demands,

And It Will Serve You

Efficiently And Effectively

34

Documents

K3L Bab#7 Electrical Safety