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Electrical Safety

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  1. Electrical Safety

  2. Introduction • Electricity is essential to modern life • Some employees work with electricity directly • Some indirectly • Electricity is a serious workplace hazard • Electricity can be productive and safe

  3. Agenda • Vocabulary • Misconceptions and myths about electricity • Electrical shock and other injuries • Electrical hazards • Electrical safety for maintenance and custodial employees • Electrical safety for offices and classrooms

  4. Voltage Low voltage High voltage Current Resistance Conductor Insulator Ohm’s law Vocabulary

  5. Voltage • Electromotive force • Electrical potential energy • “Pressure” • Measured in volts (V)

  6. Low Voltage • Electrical installations and electrical equipment operating or intended to operate on systems of 600 volts, nominal, or less. • All work performed directly on or in proximity to such electrical installations, equipment, or systems.

  7. High Voltage • Electrical installations and electrical equipment operating or intended to operate on systems of more than 600 volts. • All work performed directly on or in proximity to such electrical installations, equipment, or systems. • Beyond the scope of this training.

  8. Current • The continuous movement of electrons past a given point • Measured in amperes (amps) (A) • Sometimes the symbol “I” is used

  9. Resistance • Opposition to the movement of electrons • Resistance is used for direct current • Measured in ohms (Ω) • “Impedance” is the proper term for alternating current • “Resistance” is commonly used

  10. Conductor • A person who collects tickets on trains • A person who leads a orchestra, band, or choir

  11. Conductor • A substance or thing that allows electricity (or heat) to flow by passing energy from particle to particle • Silver, copper, gold, aluminum

  12. Insulator • A barrier that wraps conductive materials to protective against electric shock • A material with little or no conductive properties • High resistance • Glass, rubber, mica, and some plastics

  13. Ohm’s Law • R = V / A • One volt will cause a current of one ampere to flow through a conductor having the resistance of one ohm • V = A * R

  14. Ohm’s Law V (Volts) A (Amps) R (Ohms)

  15. Electrical Misconceptions • Electricity tends to go to ground • After it reaches ground, it disappears • Ground serves as just one of the electrical loops that misdirected current can use to get back to the grounded power source

  16. Misconception #2 • If an electrical appliance or tool falls into a sink or tub of water, the item will short and trip the circuit breaker • This may not happen because the sink or tub may be non-conductive and therefore not part of the loop to ground

  17. Misconception #3 • AC reverse polarity is not hazardous • Many tools have switches in only one of the two conductors serving the item • The switch is supposed to be on the “hot” conductor supplying he power

  18. Myths About Electricity • Electricity takes the path of least resistance • Current will take any conductive paths, high or low resistance, in order to return to the source that provides it power • Small amounts of current will flow through paths of high resistance

  19. Myth #2 • Double insulated power tools are doubly safe and will always provide safety • Double insulated power tools can be hazardous if dropped into water • Electrical current can flow out of the power tool into the water

  20. Myth #3 • It takes high voltage to kill;120 volts AC is not dangerous • Current is the culprit that kills • Voltage is a factor in determining how much current will flow

  21. Electrical Shock • A sudden and accidental stimulation of the body’s nervous system by an electrical current • Current will flow through the body when it becomes part of an electrical circuit

  22. Electrical Shock Dynamics

  23. Other Injuries • Burns • Falls • Injuries when machinery starts suddenly

  24. Electrical Burns • Current passing through tissue generates extreme heat • Skin damage at entry and exit • Internal tissue damage • Result from arcs or flashes • Thermal burns from overheated wires or equipment or fires

  25. Falls • Initiated by a shock • Muscles contract involuntarily • Worker can lose balance and fall

  26. Machinery Injuries • Unexpected activation • Shock • Pinch • Crush • Shear

  27. Electrical Hazards • Bare conductors • Insulation failure • Equipment failure • Static electricity • Heating and overheating • Electrical explosions

  28. Bare Conductors • Live overhead wires most common • Working on rooftops • Repair of electrical systems • Capacitors

  29. Insulation Failure • Heat and elevated temperatures • Moisture and humidity • Mechanical damage • Rodents, fungi • Chemical incompatibility

  30. Equipment Failure • Older portable tools • Energized housing • Broken connections • Wrongly replaced internal wiring • Lack of grounding plug

  31. Static Electricity • Occurs when two different materials contact and then separate • High voltage, low current • Flammable liquids • Lightning

  32. Heating and Overheating • Use of electricity results in heat • Can cause accidental fires • Burns out equipment • Equipment failure and ignition • Hot surfaces

  33. Electrical Explosions • Rapid overheating from overcurrents • Caused by short circuits, power surges, or lightning • Heated contaminants in oil-filledbreakers or transformers • Capacitors subject to wrong polarity

  34. Safety for Maintenance and Custodial Employees • Qualified electrical workers • Engineered protection • Safety considerations • Safe practices • Lockout/tagout • Personal protective equipment (PPE)

  35. Qualified Electrical Workers • A person, designated by the district,who by reason of experience orinstruction has demonstratedfamiliarity with the operationto be performed and thehazards involved

  36. Engineered Protection • Insulation • Grounding • Circuit breakers • Fuses • Ground-fault circuit interrupters

  37. Insulation • Parts of electrical equipment coated with a low-conductive material • Rubber mats to stand on • Rubber gloves • Insulated shoes

  38. Grounding • Protects from shock • Safeguards against fire • Protects against damage to electrical equipment

  39. System Grounding • One conductor of the circuit is intentionally connected to earth • Protects against high voltage contact • Stabilizes voltage in a system

  40. Equipment Grounding • Equipment grounded by a permanent and continuous connection or bond • Provides a path for dangerous fault current to return to system ground • Enables protective devices to operate

  41. Circuit Breakers • Guard against overloads of current • Ensure current flow does not produce heat that causes temperature to rise to dangerous levels • Break the current path • Thermal • Magnetic

  42. Fuses • Guard against overloads of current • Ensure current flow does not produce heat that causes temperature to rise to dangerous levels • Break the current path • Melt when current exceeds a designated value

  43. Ground-Fault Circuit Interrupters • Fast-acting electrical device sensitive to very low levels of current imbalance due to flow to ground • Reduces duration of a shock • Not an overcurrent device like a circuit breaker or fuse

  44. Types of GFCI • Circuit-breaker type • Receptacle type • Permanently mounted type • Portable type • Cord connected type

  45. Circuit-Breaker Type • A direct replacement for a standard circuit breaker • Installed in a panelboard • Includes the functions of a standard circuit breaker • Can protect an entire branch circuit with multiple outlets

  46. Receptacle Type • A direct replacement for a standard receptacle • Protects one or more receptacle outlets • Protects additional non-GFCI type receptacles connected “down stream” • Very popular because of low cost

  47. Permanently Mounted Type • Mounted in an enclosure • Designed to be permanently wired to the supply • Frequently used around large commercial swimming pools or similar wet areas

  48. Portable Type • Designed to plug into existing non-GFCI protected outlets • Contain one or more receptacle outlets protected by the GFCI module • Easily transported from one location to another • Approved for outdoor use • Some are listed as rainproof

  49. Cord Connected Type • Consists of an attachment plug which incorporates the GFCI module • Protects the cord and any equipment attached to the cord • Plug has non-standard appearance and is equipped with test and reset buttons