Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege.edu

1. Engineering 43 ElectricalSafety Bruce Mayer, PE Licensed Electrical & Mechanical EngineerBMayer@ChabotCollege.edu

2. Electrical Circuits • Electrical Power source • Electrical Components Interconnected with Wires • Electrical user

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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)

9. Resistance Varies • Different levels of electrical resistance for each person • Ranges from 500 ohms tomany thousands of ohms • The greater the body’sresistance, the lesschance of harm • A similar voltage shockcan be minor to oneperson and deadly to another.

10. Additional Resistance • Gloves • Shoes • Mats

11. 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

12. 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

13. 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

14. 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 WHY?

15. 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.

16. 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

17. 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

18. 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

19. 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

20. 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.

21. 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