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Chapter 6

Lightning Protection

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

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Characteristics of Lightning

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

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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

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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

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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.

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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

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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

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Principles of Protection

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

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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

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Lightning Protection System

• Air Terminal• Discharge Conductor• Water Terminal• Bonding

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Air Terminal• Also known as a Lightning Rod• Traditionally ¼ inch copper rod

With sharpened point Six inches above object to be protected

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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

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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”

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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

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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

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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

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Sailboat Application• Metal masts are grounded (bonded)• Add discharge conductor to wood

mast• Shrouds and stays grounded• Keel is ground plate

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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

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Precautions for Electronics

• Before a lightning storm

• After a lightning strike

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Before Lightning Storm• Put a loop in cables

Signal Power

• Disconnect ALL unnecessary equipmentbefore, NOT DURING a lightning storm All entertainment equipment Redundant communications and navigation

equipment Disconnect power cables, if accessible Disconnect and ground antennas

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Before Lightning Storm 2• If underway, keep operational

One VHF radio One GPS / chart plotter Radar, if so equipped

• Handhelds stored below

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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

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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