Electrical Safety. Introduction

Transcription

1 Electrical Safety Introduction Electrical hazards 300 electrocutions every year in the U.S. Leading cause is insufficient training ALL were preventable

2 What is Electricity? How Electricity Works Created by a generator Electrical current flows through conductors or wires Pressure measured in Volts Flow measured in Amps NFPA & NEC adopts standards & regulations

3 What is Electricity? Resistance Term for the restriction of electrical flow An opposing force Measured in Ohms Affected by: Size Temperature Material used

4 What is Electricity? Conductors Readily conduct electricity Mostly metals and metal alloys Offer little resistance to flow

5 What is Electricity? Insulators Offer high resistance to electrical flow Prevent electricity from flowing to unwanted areas Made from: Rubber Porcelain Bakelite Plastics

6 Electrical Hazards Electrical Shock Occurs when the body completes electrical circuit Occurs from contact with (3 causes): Both hot and neutral or ground wires of a circuit An energized circuit while victim is grounded Energized material

7 Electrical Hazards Severity of a Shock Depends on 3 primary factors Amount of current Path of current Duration of current

8 Electrical Hazards Shock Symptoms May depend on: Voltage and resistance Type of circuit Path of entry/exit to body Range from mild to severe Severe symptoms include: Cardiac arrest Combustion Death

9 Electrical Hazards Electrical Shock Injuries Typical Injuries Electrical burns Arc burns Thermal contact burns Damage caused by heat generated by electrical flow Prevent contact with energized circuits at all times

10 Preventing Electrical Hazards Insulation Widely used safeguard against accidental exposure Federal regulations require for circuit conductors Insulation varies depending on intended use Always inspect for deterioration before use Always confirm good condition

11 Preventing Electrical Hazards Guarding Required for energized equipment operating at 50 volts or more Methods: Limit access to only qualified persons Use permanent barriers to restrict unqualified persons Locate equipment 8 feet or more above the floor In addition, post warning signs

12 Preventing Electrical Hazards Grounding Secondary method of shock prevention Earth serves as the ultimate grounding system Grounding rods should be driven 6 to 8 feet into the earth

13 Preventing Electrical Hazards Double Insulation Tools Some modern tools don t use grounding Use double insulation Always ensure tools are in good operating condition

14 Protective Devices Circuit Protection Devices Three basic types Fuses Circuit Breakers Ground Fault Circuit Interrupter-GFCI Your safety depends on your knowledge of each of these systems.

15 Protective Devices Safety Fuses: History First protective device Originally made of thin metal Designed to fail at set current flow which was measured in Amps

16 Protective Devices Safety Fuses Three basic types Plug and Type S--visible fusible link Time Delay--allows for temporary overloads Cartridge--no visible sign of overload

17 Protective Devices Safety Fuses: User Guide Used throughout industry and home equipment Designed to protect people and equipment from danger Replace fuses with the same type and amperage rating Shut off power to replace Stand on dry ground

18 Protective Devices Time Delay Fuses Used in heavy demand start-up circuits such as motors Allows for minor peak overload without tripping Can trip and reset itself

19 Protective Devices Circuit Breakers Complex mechanical device Can be reset a limited number of times Eventually wear out Should never be used as a switch

20 Protective Devices Fuses vs. Breakers Fuses carry higher risk of fire due to: being loose corroded connections improper sizing Breakers are preferred Longer-lasting Better connection Less fire risk Preferred choice

21 Protective Devices GFCI - Ground Fault Circuit Interrupters Senses current leaking to ground and stops flow Measures current change between hot and neutral wires If current differs, GFCI will trip

22 Protective Devices GFCI s: Uses/Limitations Provide ideal protection in wet conditions Required by Code in wet and damp environments Does not provide absolute shock protection

23 Job Site Hazards Overhead power lines Contact with power lines leading cause of job site electrocutions De-energize power lines if possible Use guarding or insulation

24 Job Site Hazards OSHA Standards Maintain minimum of 10 distance from overhead power lines for crane and derrick operations For line voltage of 50,00 volts or more: Each increase of 10,000 volts requires an extra 4 distance Danger of arcing requires caution

25 Job Site Hazards Underground electrical lines Buried electrical lines ranging from 24 to 50,000 volts are common Especially dangerous when no reliable drawings are available or utilities are not located and marked

26 Job Site Hazards Work Practices Underground Electrical Notify utility operators Locate & mark underground utilities/hazards Hand dig within 24 inches of all identified utilities Always use a trained spotter

27 Job Site Hazards Temporary power GFCIs or Assured Equipment Grounding required GFCIs preferred method Competent Person to inspect and test Tag Defective Equipemnt and don t use until Repaired and/or replaced Record inspection and testing results

28 Electrical Safety--Summing Up What You Need to Do Know electrical concepts and components Anticipate/prevent electrical hazards Follow work best-practices Protect yourself and your co-workers!

29 Conclusion Safety Mastery = Knowledge Professionalism Career opportunities Success!