Transcript WATKINS - Chabot College

Engineering 43
Electrical
Safety
Bruce Mayer, PE
Licensed Electrical & Mechanical Engineer
[email protected]
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Electrical Circuits
 Electrical Power
source
 Electrical
Components
Interconnected
with Wires
 Electrical user
Engineering-43: Engineering Circuit Analysis
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Rules of Electricity
 Electricity Travels In
A Completed Circuit
 Electricity Always
Travels In The Path
Of Least Resistance
 Electricity Tries To
Travel To Earth
Ground
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
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Electricity and People
 A Person Usually
Offers Low Resistance
For The Electricity
 The Person Forms A
Completed Circuit
When Touching The
Ground
 Electricity Always Tries
To Travel To Ground
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Conditions for Electrical Shock
 Source of Electrical
Potential (Voltage)
• Relative to EARTH GND
– Most Electricity Will Flow
Into the DIRT
 An Electrical Conductor
(a Person)
 Completed Connection
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Volts and Amperes
 Voltage = Amps X Ohms
(Ω = Resistance)
 Ω’s Converts Volts To Amps
 Typical Industrial Voltages
• 115 Volts AC
 60 milliAmps (mA) Shock
• 230 Volts AC
 120 mA Shock
• 460 Volts AC
 240 mA Shock
Engineering-43: Engineering Circuit Analysis
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Effects on the Human Body
 1 mA: Can Be Felt By The Body
 2-10 mA: Minor shock, May result in a fall
 10-25 mA: Loss of Muscle Control, May
Not Be Able To Let Go Of The Current
 25-75 mA: Painful, May
Lead to Collapse or Death
 75-300 mA: If Lasts for more than
¼ Second, Almost Always FATAL
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Body’s Resistance
 Skin Offers Most Of The Body’s
Electrical Resistance
 Increased Resistance
• Thick and Callused Skin (Foot or Hand)
• Dry skin
 Decreased resistance
• Thin Skin (Inner Forearm)
• Wet or Sweaty Skin
• Broken or Abraded Skin (Scratches)
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Resistance Varies
 Different levels of electrical resistance
for each person
 Ranges from 500 ohms to
many thousands of ohms
 The greater the body’s
resistance, the less
chance of harm
 A similar voltage shock
can be minor to one
person and deadly to another.
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Additional Resistance
 Gloves
 Shoes
 Mats
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Bruce Mayer, PE
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Hazard Control
 Electrical Systems Are Inherently Safe
 Injuries Typically Occur When:
• Procedures Are Inappropriate
• Procedures Are Not Followed Or Ignored
• Safety Systems Are Circumvented
1866 - Werner Siemens (1816-1892)
perfects the dynamo, a generator in
which part of the generator's working
current is used to power the field
windings, eliminating both the need for
permanent magnets and one of the
basic limits to generating electric power
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
General Electrical Hazards
 High-voltage overhead
power lines
 Damaged insulation on wires
 Digging or trenching near
buried lines
 Broken switches or plugs
 Overloaded circuits
 Overheated appliances or tools
 Static electricity
 Flammable materials
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Portable Power Tools
 Inspect Portable Corded Power Tools
 Never Use Damaged Equipment
• Tag it out of service
• Have it repaired or replaced
 Never Use Portable Power Equipment
In Wet Or Damp Areas
 Stop Using Power Tools If They
Become Hot Or Start Sparking
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Extension Cords
 Inspect And Check
For Capacity
 For Temporary Work
only
 Do Not Use As A Rope
To Pull Or Lift Objects
 Should NOT Be
Fastened With Staples
or Hung Over Hooks
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WHY?
Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Electrical Cord Inspection




Deformed or Missing Pins
Damaged Outer Jacket Or Insulation
Evidence of Internal Damage
If Damaged, Take Out Of Service Until
Repaired
NEVER remove or bypass the
ground pin on a three-pronged
plug in order to insert it into a
non-grounded outlet.
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Bruce Mayer, PE
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Circuit Protection
 Energize or De-energize With
Appropriate Switches, Breakers, etc.
 Do Not Energize Or
De-energize With
Fuses, Terminal Lugs,
Or Cable Splice Connections
 If Circuit Protection
Device Is Tripped - inspect
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Grounding Equipment
 Most Electrical
Equipment Is Designed
With A Grounding System
 Do Not Use Equipment
With Damaged
Grounding Connectors
 Do Not Use Adapters
That Interrupt The
Grounding Connection
SP-1001 Ground
Monitor/Ground Point
• Verifies electrical ground
• Ground point for wrist
straps
• Ground point for ground
cords with banana plugs
• Provides surge protection
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Ground Fault Circuit Interrupters
 GFCIs Reduce The
Likelihood Of Fatal Shocks
 Detect Small Amount Of
Earth Current And
Automatically Switch Off Power
 Used With Extension
Cords And Portable Tools
 Standard Fuses and Circuit Breakers
Protect EQUIPMENT, NOT PEOPLE
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
What To Do In An Electrical Storm
 NOTE: Lightning surges from the clouds
to the ground along the best conductor
around, which is usually the HIGHEST
object: DON'T BE THAT CONDUCTOR!
 If you are OUTSIDE in a storm, do this:
• Seek SHELTER, preferably a house.
• Get in your VEHICLE.
• If in the open, seek LOW ground;
Sit or Lie DOWN
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Electrical Storm → DON’Ts
 Do NOT Associate Yourself with an
Electrical Conductor or be the Highest Point
• On a golf course, don't continue to play,
and never hold a metal club in your hand.
• Don't swim. If you are in the water, get out!
• If you are in a boat, get to land!
• Stay away from metal objects
that are lightning conductors.
• Don't stand under a tree. Instead of providing
shelter, a wet tree can attract lightning.
• Never stand out in the open during a storm.
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt
Summary
 Electricity Will Try To Reach
Ground Even If It Means
Going THROUGH A PERSON
 Even the “Small” Voltage From Your
Home Can Cause Serious Injury
 Always Inspect Power Tools And Cords
And Do Not Use Them If Damaged
 Do Not Attempt To Repair Electrical
Equipment Unless Trained & Qualified
Engineering-43: Engineering Circuit Analysis
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Bruce Mayer, PE
[email protected] • ENGR-43_Lec-01a_Electrical_Safety.ppt