MElec-Ch6 - 1

Chapter 6Chapter 6

Lightning ProtectionLightning Protection

MElec-Ch6 - 2

OverviewOverview

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

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

MElec-Ch6 - 3

Characteristics of Lightning

Characteristics of Lightning

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

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

MElec-Ch6 - 4

LightningLightning

• 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

• 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

MElec-Ch6 - 5

The DischargeThe 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

• 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

MElec-Ch6 - 6

Anatomy of a Lightning Stroke

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.

MElec-Ch6 - 7

Surface DispersionSurface 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

• 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

MElec-Ch6 - 8

Basic Laws or ElectricityBasic 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

• 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

MElec-Ch6 - 9

Principles of ProtectionPrinciples of Protection

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

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

MElec-Ch6 - 10

Cone of ProtectionCone of Protection• Lightning rod protects areas within its cone

60 degree cone is 99% effective 45 degree cone is 99.9% effective

• 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

MElec-Ch6 - 11

Lightning Protection System

Lightning Protection System

• Air Terminal• Discharge Conductor• Water Terminal• Bonding

• Air Terminal• Discharge Conductor• Water Terminal• Bonding

MElec-Ch6 - 12

Air TerminalAir Terminal

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

With sharpened point Six inches above object to be protected

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

With sharpened point Six inches above object to be protected

MElec-Ch6 - 13

Discharge ConductorDischarge 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

• 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

MElec-Ch6 - 14

Water TerminalWater 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

• 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”

MElec-Ch6 - 15

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

• 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

MElec-Ch6 - 16

Powerboat ApplicationPowerboat 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

• 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

MElec-Ch6 - 17

Powerboat ApplicationPowerboat 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

• Grounded metal whip provides protection

• Grounded HF whip antenna with loading coil No protection above loading coil Unless loading coil bypassed with large

conductor

MElec-Ch6 - 18

Sailboat ApplicationSailboat Application

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

mast• Shrouds and stays grounded• Keel is ground plate

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

mast• Shrouds and stays grounded• Keel is ground plate

MElec-Ch6 - 19

Precautions for PersonnelPrecautions 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

• 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

MElec-Ch6 - 20

Precautions for Electronics

Precautions for Electronics

• Before a lightning storm

• After a lightning strike

• Before a lightning storm

• After a lightning strike

MElec-Ch6 - 21

Before Lightning StormBefore 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

• 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

MElec-Ch6 - 22

Before Lightning Storm 2Before Lightning Storm 2

• If underway, keep operational One VHF radio One GPS / chart plotter Radar, if so equipped

• Handhelds stored below

• If underway, keep operational One VHF radio One GPS / chart plotter Radar, if so equipped

• Handhelds stored below

MElec-Ch6 - 23

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

• 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

MElec-Ch6 - 24

SummarySummary• 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

• 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