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Chapter 6

Chapter 6. Lightning Protection. Overview. Characteristics of Lightning Principles of Protection Precautions for Personnel Precautions for Electronic Equipment. Characteristics of Lightning. Static Electricity Ultra-High Voltage Generation The Discharge Surface Dispersion

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Chapter 6

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  1. Chapter 6 Lightning Protection

  2. Overview • Characteristics of Lightning • Principles of Protection • Precautions for Personnel • Precautions for Electronic Equipment

  3. Characteristics of Lightning • Static Electricity • Ultra-High Voltage Generation • The Discharge • Surface Dispersion • Basic Laws of Electricity

  4. Lightning • Static Electricity • Separation and storage of electrical charge • A spark is an extremely small lightning discharge • Ultra-High Voltage Generation • Surface of earth is normally negatively charged • Top of storm clouds are positively charged • Forces nearby earth to become positively charged • Develops a multimillion-volt potential

  5. The Discharge • Clouds send negative charged leaders down • Earth sends positive leaders up • From grounded sharp metal objects • Conducting path when leaders meet • Unidirectional (DC) current flow • Voltage potential 100 to 1,000 million volts • Current range 10,000 to 200,000 amperes • Duration from 1 microsecond to 1 second

  6. Current begins the return stroke, an intense wave of positive charge traveling upward about 60,000 miles per second. Electrons begin zigzagging downward in a forked pattern. This is the “stepped leader.” As the leader and streamer come together, a powerful electrical current begins flowing. As the stepped leader nears the ground, it draws a streamer of positive charge upward. Anatomy of a Lightning Stroke

  7. Surface Dispersion • Surface dispersion • Main portion of lightning bolt penetrates earth • Spurs find far-reaching paths along surface • Surface dispersion is deadly • Stay out of the water • Keep away from trees

  8. Basic Laws or Electricity • Lightning creates magnetically induced current in all metal items within its influence • The longer the wire, greater the current • The closer the strike, greater the current • Any impedance to current flow results in • Build up of high voltage at that location • Resulting in arc-over to reach ground • Ignites flammable material • Vaporizes metal of insufficient cross-section

  9. Principles of Protection • Cone of Protection • Lightning Protection System • Power Boat Applications • Sail Boat Applications

  10. Cone of Protection • Lightning rod protects areas within its cone • 60 degree cone is 99% effective • 45 degree cone is 99.9% effective • Less current flow from sharp pointed tip • More current flow from blunt or ball tip

  11. Lightning Protection System • Air Terminal • Discharge Conductor • Water Terminal • Bonding

  12. Air Terminal • Also known as a Lightning Rod • Traditionally ¼ inch copper rod • With sharpened point • Six inches above object to be protected

  13. Discharge Conductor • Not less than #4 AWG • Uninsulated stranded copper wire • “Straight” from Air Terminal to Water Terminal • No sharp bends (bend radius of 1 foot) • Should be run outside of hull • Electrical wiring should be at right angles #4

  14. Water Terminal • Also known as a Ground Plate • External to hull • Sailboats use metal keel • Area of one square foot • Not painted • No water film between plate and hull • Use bedding compound Size: 18” x 6” x ½”

  15. Bonding (Chapter 2) • Bonding is also for Lightning Protection • Purpose – keep all metal surfaces at zero potential • To prevent electrical shock • To prevent stray current corrosion • To prevent induced potential from lightning strike • Bonding conductor • Cross section of #6 AWG • Strap not less than #20 gauge (0.032 inch thick) • Normally #6 bare copper wire

  16. Powerboat Application • Fiberglass antennas provide NO protection • Add lightning rod on other side for protection • e.g. grounded metal whip antenna • Ground the signal mast or “Tuna Tower” • Need a ground plate • Stay within the cone of protection

  17. Powerboat Application • Grounded metal whip provides protection • Grounded HF whip antenna with loading coil • No protection above loading coil • Unless loading coil bypassed with large conductor

  18. Sailboat Application • Metal masts are grounded (bonded) • Add discharge conductor to wood mast • Shrouds and stays grounded • Keel is ground plate

  19. Precautions for Personnel • Remain inside the boat • Trust lightning protection system • Stay Out of the Water • Surface dispersion • Avoid contact with metal surfaces • Induced voltage • Handle only one metal control at a time

  20. Precautions for Electronics • Before a lightning storm • After a lightning strike

  21. Before Lightning Storm • Put a loop in cables • Signal • Power • Disconnect ALL unnecessary equipment before, NOT DURING a lightning storm • All entertainment equipment • Redundant communications and navigation equipment • Disconnect power cables, if accessible • Disconnect and ground antennas

  22. Before Lightning Storm 2 • If underway, keep operational • One VHF radio • One GPS / chart plotter • Radar, if so equipped • Handhelds stored below

  23. After Direct Lightning Strike • First, check crew – CPR Required? • Next, check hull – repair any new leaks • Then check navigation & safety equipment • Radios with test call, or with handheld • Magnetic compass • Verify with GPS • Deviation table may no longer be accurate • If fixed VHF Radio or GPS inoperative • Go to backup handheld unit

  24. Summary • Tremendous energy in lightning strike • Lightning protection • Based on cone of protection • Components • Air terminal • Discharge conductor (#4 AWG stranded) • Water terminal (1 sq ft) • Bond all metal above deck • Before lightning storm • Disconnect all unnecessary equipment • After lightning strike • First check people • Then hull • May have to go to backup electronics

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