Electrical Workplace Safety

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Ellectrical safety including arc flash

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Electrical Workplace Safety

  1. 1. Electrical Safe Work Practices <ul><li>Including NFPA 70E </li></ul>
  2. 2. Electricity - The Dangers <ul><li>About 5 workers are electrocuted every week </li></ul><ul><li>Causes 12% of young worker workplace deaths </li></ul><ul><li>Takes very little electricity to cause harm </li></ul><ul><li>Significant risk of causing fires </li></ul>
  3. 3. Introduction <ul><li>There are four main types of electrical injuries: </li></ul><ul><ul><li>Electrocution (death due to electrical shock) </li></ul></ul><ul><ul><li>Electrical shock </li></ul></ul><ul><ul><li>Burns </li></ul></ul><ul><ul><li>Falls </li></ul></ul>
  4. 4. Electricity – How it Works <ul><li>Electricity is the flow of energy from one place to another </li></ul><ul><li>Requires a source of power: usually a generating station </li></ul><ul><li>A flow of electrons (current) travels through a conductor </li></ul><ul><li>Travels in a closed circuit </li></ul>
  5. 5. Electrical Terminology <ul><li>Current – the movement of electrical charge </li></ul><ul><li>Resistance – opposition to current flow </li></ul><ul><li>Voltage – a measure of electrical force </li></ul><ul><li>Conductors – substances, such as metals, that have little resistance to electricity </li></ul><ul><li>Insulators – substances, such as wood, rubber, glass, and bakelite, that have high resistance to electricity </li></ul><ul><li>Grounding – a conductive connection to the earth which acts as a protective measure </li></ul>
  6. 6. Electrical Shock <ul><li>Received when current passes through the body </li></ul><ul><li>Severity of the shock depends on: </li></ul><ul><ul><li>Path of current through the body </li></ul></ul><ul><ul><li>Amount of current flowing through the body </li></ul></ul><ul><ul><li>Length of time the body is in the circuit </li></ul></ul><ul><li>LOW VOLTAGE DOES NOT MEAN LOW HAZARD </li></ul>
  7. 7. Dangers of Electrical Shock <ul><li>Currents above 10 mA* can paralyze or “freeze” muscles </li></ul><ul><li>Currents greater than 75 mA* can cause ventricular fibrillation (rapid, ineffective heartbeat) </li></ul><ul><li>Will cause death in a few minutes unless a defibrillator is used </li></ul><ul><li>75 mA is not much current – a small power drill uses 30 times as much </li></ul>* mA = milliampere = 1/1,000 of an ampere Defibrillator in use
  8. 8. How is an electrical shock received? <ul><li>When two wires have different potential differences (voltages), current will flow if they are connected together </li></ul><ul><ul><li>In most household wiring, the black wires are at 110 volts relative to ground </li></ul></ul><ul><ul><li>The white wires are at zero volts because they are connected to ground </li></ul></ul><ul><li>If you come into contact with an energized (live) black wire, and you are also in contact with the white grounded wire, current will pass through your body and YOU WILL RECEIVE A SHOCK </li></ul>
  9. 9. How is an electrical shock received? (cont’d) <ul><li>If you are in contact with an energized wire or any energized electrical component, and also with any grounded object, YOU WILL RECEIVE A SHOCK </li></ul><ul><li>You can even receive a shock when you are not in contact with a ground </li></ul><ul><ul><li>If you contact both wires of a 240-volt cable, YOU WILL RECEIVE A SHOCK and possibly be electrocuted </li></ul></ul>
  10. 10. Electrical Burns <ul><li>Most common shock-related, nonfatal injury </li></ul><ul><li>Occurs when you touch electrical wiring or equipment that is improperly used or maintained and which may produce Arc Flash </li></ul><ul><li>Typically occurs on the hands </li></ul><ul><li>Very serious injury that needs immediate attention </li></ul><ul><li>More on Arc Flash later! </li></ul>
  11. 11. Falls <ul><li>Electric shock can also cause indirect or secondary injuries </li></ul><ul><li>Workers in elevated locations who experience a shock can fall, resulting in serious injury or death </li></ul>
  12. 12. Electrical Hazards and How to Control Them <ul><li>Electrical accidents are caused by a combination of three factors: </li></ul><ul><ul><li>Unsafe equipment and/or installation, </li></ul></ul><ul><ul><li>Workplaces made unsafe by the environment, and </li></ul></ul><ul><ul><li>Unsafe work practices. </li></ul></ul>
  13. 13. Overload Hazards <ul><li>If too many devices are connected into a circuit, the current will heat the wires to a very high temperature, which may cause a fire </li></ul><ul><li>If the wire insulation melts, arcing may occur and cause a fire in the area where the overload exists, even inside a wall </li></ul>IR picture of overloaded panel
  14. 14. Hazard – Overloaded Circuits <ul><li>Hazards may result from: </li></ul><ul><li>Too many devices plugged into a circuit, causing heated wires and possibly a fire </li></ul><ul><li>Damaged tools overheating </li></ul><ul><li>Lack of overcurrent protection </li></ul>
  15. 15. Control- Electrical Protective Devices <ul><li>Automatically opens circuit if excess current from overload or ground-fault is detected – shutting off electricity </li></ul><ul><li>Include fuses, circuit breakers, and ground-fault circuit-interrupters (GFCI’s) </li></ul><ul><li>Fuses and circuit breakers are overcurrent devices </li></ul><ul><ul><li>When there is too much current: </li></ul></ul><ul><ul><ul><li>Fuses melt </li></ul></ul></ul><ul><ul><ul><li>Circuit breakers trip open </li></ul></ul></ul>
  16. 16. Grounding Hazards <ul><li>Some of the most frequently violated OSHA standards </li></ul><ul><li>Metal parts of an electrical wiring system that we touch (switch plates, ceiling light fixtures, conduit, etc.) should be at zero volts relative to ground </li></ul><ul><li>Housings of motors, appliances or tools that are plugged into improperly grounded circuits may become energized </li></ul><ul><li>If you come into contact with an improperly grounded electrical device, YOU WILL BE SHOCKED </li></ul>
  17. 17. Grounding <ul><li>Grounding creates a low-resistance path from a tool to the earth to disperse unwanted current. </li></ul><ul><li>When a short or lightning occurs, energy flows to the ground, protecting you from electrical shock, injury and death. </li></ul>
  18. 18. Hazard – Improper Grounding <ul><li>Tools plugged into improperly grounded circuits may become energized </li></ul><ul><li>Broken wire or plug on extension cord </li></ul><ul><li>Some of the most frequently violated OSHA standards </li></ul>
  19. 19. Control – Ground Tools & Equipment <ul><li>Ground power supply systems, electrical circuits, and electrical equipment </li></ul><ul><li>Frequently inspect electrical systems to insure path to ground is continuous </li></ul><ul><li>Inspect electrical equipment before use </li></ul><ul><li>Don’t remove ground prongs from tools or extension cords </li></ul><ul><li>Ground exposed metal parts of equipment </li></ul>
  20. 20. Ground fault video
  21. 21. Control – Use GFCI (ground-fault circuit interrupter) <ul><li>Protects you from shock </li></ul><ul><li>Detects difference in current between the black and white wires </li></ul><ul><li>If ground fault detected, GFCI shuts off electricity in 1/40 th of a second </li></ul><ul><li>Use GFCI’s on all 120-volt, single-phase, 15- and 20-ampere receptacles, or have an assured equipment grounding conductor program. </li></ul>
  22. 22. Control - Assured Equipment Grounding Conductor Program <ul><li>Program must cover: </li></ul><ul><ul><li>All cord sets </li></ul></ul><ul><ul><li>Receptacles not part of a building or structure </li></ul></ul><ul><ul><li>Equipment connected by plug and cord </li></ul></ul><ul><li>Program requirements include: </li></ul><ul><ul><li>Specific procedures adopted by the employer </li></ul></ul><ul><ul><li>Competent person to implement the program </li></ul></ul><ul><ul><li>Visual inspection for damage of equipment connected by cord and plug </li></ul></ul>
  23. 23. Hazard – Exposed Electrical Parts <ul><li>Cover removed from wiring or breaker box </li></ul>
  24. 24. Control – Isolate Electrical Parts <ul><li>Use guards or barriers </li></ul><ul><li>Replace covers </li></ul>Guard live parts of electric equipment operating at 50 volts or more against accidental contact
  25. 25. Control – Isolate Electrical Parts - Cabinets, Boxes & Fittings <ul><li>Conductors going into them must be protected, and unused openings must be closed </li></ul>
  26. 26. Guarding of Live Parts <ul><li>Must enclose or guard electric equipment in locations where it would be exposed to physical damage </li></ul><ul><li>Violation shown here is physical damage to conduit </li></ul>
  27. 27. Cabinets, Boxes, and Fittings <ul><li>Junction boxes, pull boxes and fittings must have approved covers </li></ul><ul><li>Unused openings in cabinets, boxes and fittings must be closed (no missing knockouts) </li></ul><ul><li>Photo shows violations of these two requirements </li></ul>
  28. 28. Guarding of Live Parts <ul><li>Must guard live parts of electric equipment operating at 50 volts or more against accidental contact by: </li></ul><ul><ul><li>Approved cabinets/enclosures, or </li></ul></ul><ul><ul><li>Location or permanent partitions making them accessible only to qualified persons, or </li></ul></ul><ul><ul><li>Elevation of 8 ft. or more above the floor or working surface </li></ul></ul><ul><li>Mark entrances to guarded locations with conspicuous warning signs </li></ul>
  29. 29. Hazard - Overhead Power Lines <ul><li>Usually not insulated </li></ul><ul><li>Examples of equipment that can contact power lines: </li></ul><ul><ul><li>Crane </li></ul></ul><ul><ul><li>Ladder </li></ul></ul><ul><ul><li>Scaffold </li></ul></ul><ul><ul><li>Backhoe </li></ul></ul><ul><ul><li>Scissors lift </li></ul></ul><ul><ul><li>Raised dump truck bed </li></ul></ul><ul><ul><li>Aluminum paint roller </li></ul></ul>
  30. 30. Control - Overhead Power Lines <ul><li>Stay at least 10 feet away </li></ul><ul><li>Post warning signs </li></ul><ul><li>Assume that lines are energized </li></ul><ul><li>Use wood or fiberglass ladders, not metal </li></ul><ul><li>Power line workers need special training & PPE </li></ul>
  31. 31. Hand-Held Electric Tools <ul><li>Hand-held electric tools pose a potential danger because they make continuous good contact with the hand </li></ul><ul><li>To protect you from shock, burns, and electrocution, tools must: </li></ul><ul><ul><li>Have a three-wire cord with ground and be plugged into a grounded receptacle, or </li></ul></ul><ul><ul><li>Be double insulated, or </li></ul></ul><ul><ul><li>Be powered by a low-voltage isolation transformer </li></ul></ul>
  32. 32. Tool Safety Tips <ul><li>Use gloves and appropriate footwear </li></ul><ul><li>Store in dry place when not using </li></ul><ul><li>Don’t use in wet/damp conditions </li></ul><ul><li>Keep working areas well lit </li></ul><ul><li>Ensure not a tripping hazard </li></ul><ul><li>Don’t carry a tool by the cord </li></ul><ul><li>Don’t yank the cord to disconnect it </li></ul><ul><li>Keep cords away from heat, oil, & sharp edges </li></ul><ul><li>Disconnect when not in use and when changing accessories such as blades & bits </li></ul><ul><li>Remove damaged tools from use </li></ul>
  33. 33. <ul><li>More vulnerable than fixed wiring </li></ul><ul><li>Do not use if one of the recognized wiring methods can be used instead </li></ul><ul><li>Flexible cords can be damaged by: </li></ul><ul><ul><li>Aging </li></ul></ul><ul><ul><li>Door or window edges </li></ul></ul><ul><ul><li>Staples or fastenings </li></ul></ul><ul><ul><li>Abrasion from adjacent materials </li></ul></ul><ul><ul><li>Activities in the area </li></ul></ul><ul><li>Improper use of flexible cords can cause shocks, burns or fire </li></ul>Use of Flexible Cords
  34. 34. Flexible cord <ul><li>DO NOT use flexible wiring where frequent inspection would be difficult or where damage would be likely. </li></ul><ul><li>Flexible cords must not be . . . </li></ul><ul><ul><li>run through holes in walls, ceilings, or floors; </li></ul></ul><ul><ul><li>run through doorways, windows, or similar openings (unless physically protected); </li></ul></ul><ul><ul><li>hidden in walls, ceilings, floors, conduit or other raceways. </li></ul></ul>
  35. 35. Hazard - Inadequate Wiring <ul><li>Hazard - wire too small for the current </li></ul><ul><li>Example - portable tool with an extension cord that has a wire too small for the tool </li></ul><ul><ul><li>The tool will draw more current than the cord can handle, causing overheating and a possible fire without tripping the circuit breaker </li></ul></ul><ul><ul><li>The circuit breaker could be the right size for the circuit but not for the smaller-wire extension cord </li></ul></ul>Wire gauge measures wires ranging in size from number 36 to 0 American wire gauge (AWG) Wire Gauge WIRE
  36. 36. Control – Use the Correct Wire <ul><li>Wire used depends on operation, building materials, electrical load, and environmental factors </li></ul><ul><li>Use fixed cords rather than flexible cords </li></ul><ul><li>Use the correct extension cord </li></ul>Must be 3-wire type and designed for hard or extra-hard use
  37. 37. Hazard – Defective Cords & Wires <ul><li>Plastic or rubber covering is missing </li></ul><ul><li>Damaged extension cords & tools </li></ul>
  38. 38. Hazard – Damaged Cords <ul><li>Cords can be damaged by: </li></ul><ul><ul><li>Aging </li></ul></ul><ul><ul><li>Door or window edges </li></ul></ul><ul><ul><li>Staples or fastenings </li></ul></ul><ul><ul><li>Abrasion from adjacent materials </li></ul></ul><ul><ul><li>Activity in the area </li></ul></ul><ul><li>Improper use can cause shocks, burns or fire </li></ul>
  39. 39. Control – Cords & Wires <ul><li>Insulate live wires </li></ul><ul><li>Check before use </li></ul><ul><li>Use only cords that are 3-wire type </li></ul><ul><li>Use only cords marked for hard or extra-hard usage </li></ul><ul><li>Use only cords, connection devices, and fittings equipped with strain relief </li></ul><ul><li>Remove cords by pulling on the plugs, not the cords </li></ul><ul><li>Cords not marked for hard or extra-hard use, or which have been modified, must be taken out of service immediately </li></ul>
  40. 40. Avoid Wet Conditions <ul><li>If you touch a live wire or other electrical component while standing in even a small puddle of water you’ll get a shock. </li></ul><ul><li>Damaged insulation, equipment, or tools can expose you to live electrical parts. </li></ul><ul><li>Improperly grounded metal switch plates & ceiling lights are especially hazardous in wet conditions. </li></ul><ul><li>Wet clothing, high humidity, and perspiration increase your chances of being electrocuted. </li></ul>
  41. 41. Clues that Electrical Hazards Exist <ul><li>Tripped circuit breakers or blown fuses </li></ul><ul><li>Warm tools, wires, cords, connections, or junction boxes </li></ul><ul><li>GFCI that shuts off a circuit </li></ul><ul><li>Worn or frayed insulation around wire or connection </li></ul>
  42. 42. Training <ul><li>Deenergizing electric equipment before inspecting or making repairs </li></ul><ul><li>Using electric tools that are in good repair </li></ul><ul><li>Using good judgment when working near energized lines </li></ul><ul><li>Using appropriate protective equipment </li></ul>Train employees working with electric equipment in safe work practices, including:
  43. 43. Recent Changes <ul><li>Attention to Personnel Protection (PPE) </li></ul><ul><li>Recognition of Unsafe Work Practices </li></ul><ul><li>Impact to Business and Medical Costs </li></ul><ul><li>Changes to NFPA 70E & NEC </li></ul><ul><li>IEEE Standard for Arc Flash Analysis </li></ul><ul><li>Requirements of OSHA 1910, Subpart S applies when contractors are connecting to existing circuits </li></ul>
  44. 44. What Does OSHA Say? NEC & NFPA must be followed! <ul><li>29 CFR 1910.333 </li></ul><ul><ul><li>Live electrical parts that an employee may be exposed shall be de-energized unless additional or greater hazards are introduced. (NFPA 70E 130.1) </li></ul></ul><ul><li>29 CFR 1910.335 </li></ul><ul><ul><li>Employees working in areas where potential electrical hazards (including shock and arc flash) exist shall be provided with and shall use personal protective equipment. Written permit also required. </li></ul></ul><ul><ul><li>(NEC 110.16 & NFPA 130.1(A)(1)) </li></ul></ul>
  45. 45. Lockout and Tagging of Circuits <ul><li>Apply locks to power source after de-energizing </li></ul><ul><li>Tag deactivated controls </li></ul><ul><li>Tag de-energized equipment and circuits at all points where they can be energized </li></ul><ul><li>Tags must identify equipment or circuits being worked on </li></ul>
  46. 46. Industry Standards and Regulations <ul><li>OSHA 29 CFR 1910 & 1926 </li></ul><ul><ul><ul><li>OSHA & Code inspectors enforce NEC 110.16 & NFPA 70E </li></ul></ul></ul><ul><li>NFPA 70E-2004 </li></ul><ul><ul><ul><li>Requires de-energizing circuit unless infeasible </li></ul></ul></ul><ul><ul><ul><li>When circuit worked on is energized, permit required </li></ul></ul></ul><ul><ul><ul><li>Requires shock and arc flash boundaries </li></ul></ul></ul><ul><ul><ul><li>Requires specific personal protective equipment </li></ul></ul></ul><ul><li>NEC 110.16-2005 </li></ul><ul><ul><ul><li>Requires NFPA 70E markings warning of ARC Flash </li></ul></ul></ul>
  47. 47. NEC 2005 <ul><li>110.16 Flash Protection. Switchboards, panel boards, industrial control panels, and motor control centers in other than dwelling occupancies, that are likely to require examination, adjustment, servicing, or maintenance while energized, shall be field marked to warn qualified persons of potential electric arc flash hazards. The marking shall be located so as to be clearly visible to qualified persons before examination, adjustment, servicing, or maintenance of the equipment. </li></ul>
  48. 48. Sample NEC Warning Article 110.16
  49. 49. Energized Electrical Work Written Permit REQUIRED ELEMENTS* <ul><li>A description of the circuit and equipment to be worked on and their location </li></ul><ul><li>Justification for why the work must be performed in an energized condition (130.1) </li></ul><ul><li>A description of the safe work practices to be employed </li></ul><ul><li>Results of the shock hazard analysis </li></ul><ul><li>Determination of shock protection boundaries [130.2(B) and Table 130.2(C)] </li></ul><ul><li>Results of the flash hazard analysis (130.3) </li></ul><ul><li>The Flash Protection Boundary [130.3(A)] </li></ul><ul><li>The necessary personal protective equipment to safely perform the assigned task [130.3(B), 130.7(C)(9), and Table 130.7(C)(9)(a)] </li></ul><ul><li>Means employed to restrict the access of unqualified persons from the work area [110.8(A)(2)] </li></ul><ul><li>Evidence of completion of a job briefing, including a discussion of any job-specific hazards [110.7(G)] </li></ul><ul><li>Energized work approval (authorizing or responsible management, safety officer, or owner, etc.) signature! </li></ul>*requirements are found in referenced sections of NFPA 2004
  50. 50. Exemptions to Work Permit <ul><ul><li>Work performed on or near live parts by qualified persons related to tasks such as testing, troubleshooting, voltage measuring, etc., shall be permitted to be performed without an energized electrical work permit, provided appropriate safe work practices and personal protective equipment in accordance with NFPA 70E Chapter 1 are provided and used. </li></ul></ul>
  51. 51. Why is ARC-FLASH Protection such an issue? <ul><li>As much as 80% of all electrical injuries are burns resulting from an arc-flash and ignition of flammable clothing. </li></ul><ul><li>OSHA estimates between 5 and 10 persons per day are electrically burned severe enough to require treatment at special burn centers! </li></ul><ul><li>Arc temperature can reach 35,000°F - this is four times hotter than the surface of the sun </li></ul><ul><li>Fatal burns can occur at distances over 10 ft . </li></ul>
  52. 52. ARC EXPOSURE ENERGY BASICS <ul><li>Exposure Energy is Expressed in cal/cm 2 /0.1sec </li></ul><ul><ul><li>The calorie (symbol: cal) is the amount of heat (energy) required to raise the temperature of one gram of water by 1 °C . </li></ul></ul><ul><li>1 cal/cm 2 Equals the Exposure on the tip of a finger by a Cigarette Lighter in One Second </li></ul><ul><li>An Exposure Energy of Only One or Two cal/cm 2 Will Cause a 2nd Degree Burn on Human Skin </li></ul>
  53. 53. ARC Flash Analysis <ul><li>OSHA 1910.132, .145,.303,.335, 1926.95, .403, .404, .405 </li></ul><ul><li>Where work will be performed within the flash protection boundary, the flash hazard analysis shall determine, and the employer shall document, the incident energy exposure to the worker which shall determine the level of Flame resistant (FR) clothing and PPE to be used by the employee based upon the incident energy exposure associated with the specific task. </li></ul><ul><li>As an alternative, PPE requirements of NFPA 70E Part II 3-3.9 may be used in lieu of a detailed flash hazard analysis. </li></ul>
  54. 54. Hazard Risk Category Classification <ul><li>NFPA 70E – Hazard Risk 0 </li></ul><ul><ul><ul><ul><li>This hazard risk category poses minimal risk. </li></ul></ul></ul></ul><ul><li>NFPA 70E – Hazard Risk 1 </li></ul><ul><ul><ul><ul><li>This hazard risk category poses some risk. </li></ul></ul></ul></ul><ul><li>NFPA 70E – Hazard Risk 2 </li></ul><ul><ul><ul><ul><li>This hazard risk category involves tasks that pose a moderate risk. </li></ul></ul></ul></ul><ul><li>NFPA 70E – Hazard Risk 3 </li></ul><ul><ul><ul><ul><li>This hazard risk category involves tasks that pose a high risk. </li></ul></ul></ul></ul><ul><li>NFPA 70E – Hazard Risk 4 </li></ul><ul><ul><ul><ul><li>This hazard risk category represents tasks that pose the greatest risk. </li></ul></ul></ul></ul>
  55. 55. Hazard Risk Category Tables Table 130.7(C)(9)
  56. 56. PPE Matrix based upon Hazard Risk Category Table 130.7(C)(10)
  57. 57. Preventing Electrical Hazards - PPE <ul><ul><ul><li>Proper foot protection (not tennis shoes) </li></ul></ul></ul><ul><ul><ul><li>Rubber insulating gloves, hoods, sleeves, matting, and blankets </li></ul></ul></ul><ul><ul><ul><li>Hard hat (insulated - nonconductive) </li></ul></ul></ul><ul><ul><ul><li>FR clothing </li></ul></ul></ul>
  58. 58. What are the shock approach and flash protection boundaries?
  59. 59. Flash Protection Boundary (FPB) <ul><li>The safe approach distance from energized equipment or parts </li></ul><ul><li>4 feet for low voltage ( < 600V ) systems </li></ul><ul><li>FPB to be calculated which may decrease the boundary distance </li></ul><ul><li>crossing into FPB requires wearing the appropriate PPE </li></ul><ul><li>A qualified person must accompany unqualified persons </li></ul><ul><li>Defined as the distance at which the worker is exposed to 1.2 cal/cm2 for 0.1 second </li></ul><ul><li>IEEE Std 1584 - 2002 details the procedure and needed equations for arc flash calculations. The equations are used to calculate the incident energy and flash boundary. The IEEE procedure is valid for voltages ranging from 208V volts to 15kV with gap ranges between 3 mm. and 153 mm . </li></ul>
  60. 60. Limited Approach Boundary <ul><li>A shock protection boundary to be crossed by only qualified persons </li></ul><ul><li>Unqualified persons must be escorted by a qualified person </li></ul><ul><li>Minimum distance from energized item allowed for unqualified personnel </li></ul><ul><li>Determined by NFPA 70E Table 130.2(C) based on voltage of equipment </li></ul><ul><li>Qualified persons must use the appropriate PPE </li></ul><ul><li>Qualified persons must be trained to perform the required work </li></ul>
  61. 61. Restricted Approach Boundary <ul><li>A shock protection boundary to be crossed by only qualified persons </li></ul><ul><li>Requires use of shock protection techniques & equipment when crossed </li></ul><ul><li>Qualified persons must use the appropriate PPE </li></ul><ul><li>Qualified persons must be trained to perform the required work </li></ul><ul><li>Must have a written approved plan for the work that they will perform </li></ul><ul><li>Must plan the work to keep all parts of the body out of the Prohibited Space </li></ul><ul><li>Determined by NFPA 70E Table 130.2(C) based on voltage of equipment </li></ul>
  62. 62. Prohibited Approach Boundary <ul><li>Considered the same as making contact with exposed energized parts therefore must do the following: </li></ul><ul><li>Have specified training to work on energized conductors or parts </li></ul><ul><li>Have a documented plan justifying the need to work that close </li></ul><ul><li>Perform a risk analysis </li></ul><ul><li>Have (2) and (3) approved by authorized management </li></ul><ul><li>Use appropriate personal protective equipment rated for the voltage and energy level involved </li></ul>
  63. 63. Approach Boundaries Table 130.2(C) 3 ft. 1 in. 3 ft. 7 in. 10 ft.0 in. 11 ft. 0 in. 138 – 145 kV 2 ft. 8 in. 3 ft. 3 in. 8 ft.0 in. 10 ft. 8 in. 72.6 – 121 kV 2 ft. 1 in. 3 ft. 3 in. 8 ft.0 in. 10 ft. 0 in. 46.1 – 72.5 kV 1 ft. 5 in. 2 ft. 10 in. 8 ft.0 in. 10 ft. 0 in. 36.1 – 46 kV 0 ft. 10 in. 2 ft. 7 in. 6 ft.0 in. 10 ft. 0 in. 15.1 – 36 kV 0 ft. 7 in. 2 ft. 2 in. 5 ft.0 in. 10 ft. 0 in. 751V - 15 kV 0 ft. 1 in. 1 ft. 0 in. 3 ft.6 in. 10 ft. 0 in. 301 - 750 Avoid contact Avoid contact 3 ft.6 in. 10 ft. 0 in. 51 - 300 Not specified Not specified Not specified Not specified 0 - 50 Includes Inadvertent Movement Adder Exposed Fixed Circuit Part Exposed Moveable Conductor Phase-to-Phase Prohibited Approach Boundary Restricted Approach Boundary Limited Approach Boundary Nominal System Voltage Range
  64. 64. Preventing Electrical Hazards - Summary <ul><li>Plan your work with others </li></ul><ul><li>Plan to avoid falls </li></ul><ul><li>Plan to lock-out and tag-out equipment </li></ul><ul><li>Follow NFPA 70E </li></ul><ul><li>Remove jewelry </li></ul><ul><li>Avoid wet conditions and overhead power lines </li></ul>
  65. 65. Safe Distance Equations <ul><li>The short-circuit symmetrical ampacity from a bolted 3-phase fault at the transformer terminals is calculated with the following formula: </li></ul><ul><li>I SC = {[MVA Base x 10 6 ] ÷ [1.732 x V]} x {100 ÷ %Z} </li></ul><ul><li>where I SC is in amperes, V is in volts, and % Z is based on the transformer MVA . </li></ul><ul><li>A typical value for the maximum power (in MW) in a 3-phase arc can be calculated using the following formula: </li></ul><ul><li>P = [ Maximum bolted fault MVA bf ] x 0.707 2 </li></ul><ul><li>The Flash Protection Boundary distance is calculated in accordance with the following formula: </li></ul>
  66. 66. Methods of Reducing Hazard Risk <ul><li>Specifying Current Limiting Fuses on Low Voltage Switchgear Breakers </li></ul><ul><li>Specifying ARC Resistance Medium Voltage Switchgear </li></ul><ul><li>Remote Control of Switchgear Breakers </li></ul><ul><li>High Resistance Grounding on Low Voltage and Medium Voltage (15kV and below) Systems </li></ul>

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