Lightning Protection Chapter 6 PowerPoint slides by Stf/C Harl Porter, SN Marine Electronics 107Harl@sc.rr.com Rear Commander for Electro-Mechanical Systems is R/C Gene Danko, SN

Overview Characteristics of Lightning Principles of Protection Precautions for Personnel Precautions for Electronic Equipment Major sections in this chapter

Characteristics of Lightning Static Electricity Ultra-High Voltage Generation The Discharge Surface Dispersion Basic Laws of Electricity Topics in this section

Lightning Static Electricity Ultra-High Voltage Generation 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 (No notes)

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 (No notes)

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. Copied from page 132 of The Weather Book by USA Today. USPS has their permission to use their Art Work in our classes.

Surface Dispersion Surface dispersion Surface dispersion is deadly 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 Know that are no trees in water Are not a safe place during a lightning storm If lightning hits tree, it may explode Also get surface dispersion around tree as tree is not always a good ground

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 (No notes)

Principles of Protection Cone of Protection Lightning Protection System Power Boat Applications Sail Boat Applications Topics in this section

Cone of Protection Lightning rod protects areas within its cone 60 degree cone is 99% effective 45 degree cone is 99.9% effective Fig 6-1 Less current flow from sharp pointed tip More current flow from blunt or ball tip

Lightning Protection System Air Terminal Discharge Conductor Water Terminal Bonding Topics in this section

Air Terminal Also known as a Lightning Rod Traditionally ¼ inch copper rod With sharpened point Six inches above object to be protected Blunt object will have more intense discharge

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 Split bolt for joining cables together #8 AWG solid copper wire at top #4 AWG solid copper wire in middle #4 AWG stranded tinned copper wire at bottom Lower left is Split-bolt connector With South Carolina Quarter #4

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 Note size of commercial water terminal Need one square foot in sea water and four square feet in fresh water If have water between plate and hull, may turn to steam during a lightning strike and “blast” a hole in hull Size: 18” x 6” x ½”

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 (No notes)

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 (No notes)

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 Fig 6-2

Sailboat Application Metal masts are grounded (bonded) Add discharge conductor to wood mast Shrouds and stays grounded Keel is ground plate Fig 6-3

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 (No notes)

Precautions for Electronics Before a lightning storm After a lightning strike Topics in this section

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 (No notes)

Before Lightning Storm 2 If underway, keep operational One VHF radio One GPS / chart plotter Radar, if so equipped Handhelds stored below Want handhelds off and stored well inside cone of protection Fixed equipment may be damaged by a 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 People first Boat second Then electronics

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 (No notes)