Chapter 6 Lightning Protection 1 Overview Characteristics of

Chapter 6 Lightning Protection 1

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

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

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 4

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 5

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

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 7

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 8

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

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 10

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

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

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 13

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” 14

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 15

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 16

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 17

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

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 19

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

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 21

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

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 23

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 24