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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
Chapter 6

Lightning Protection

overview
Overview
  • Characteristics of Lightning
  • Principles of Protection
  • Precautions for Personnel
  • Precautions for Electronic Equipment
characteristics of lightning
Characteristics of Lightning
  • Static Electricity
  • Ultra-High Voltage Generation
  • The Discharge
  • Surface Dispersion
  • Basic Laws of Electricity
lightning
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
the discharge
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
anatomy of a lightning stroke

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
surface dispersion
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
basic laws or electricity
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
principles of protection
Principles of Protection
  • Cone of Protection
  • Lightning Protection System
  • Power Boat Applications
  • Sail Boat Applications
cone of protection
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
lightning protection system
Lightning Protection System
  • Air Terminal
  • Discharge Conductor
  • Water Terminal
  • Bonding
air terminal
Air Terminal
  • Also known as a Lightning Rod
  • Traditionally ¼ inch copper rod
    • With sharpened point
    • Six inches above object to be protected
discharge conductor
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

water terminal
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”

bonding chapter 2
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
powerboat application
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
powerboat application17
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
sailboat application
Sailboat Application
  • Metal masts are grounded (bonded)
  • Add discharge conductor to wood mast
  • Shrouds and stays grounded
  • Keel is ground plate
precautions for personnel
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
precautions for electronics
Precautions for Electronics
  • Before a lightning storm
  • After a lightning strike
before lightning storm
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
before lightning storm 2
Before Lightning Storm 2
  • If underway, keep operational
    • One VHF radio
    • One GPS / chart plotter
    • Radar, if so equipped
  • Handhelds stored below
after direct lightning strike
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
summary
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