MElec-Ch6 - 1

1
Chapter 6

• Lightning Protection

2
Overview

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

3
Characteristics of Lightning

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

4
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

5
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

6
Anatomy of a Lightning Stroke
7
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

8
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

9
Principles of Protection

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

10
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

11
Lightning Protection System

• Air Terminal
• Discharge Conductor
• Water Terminal
• Bonding

12
Air Terminal

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

13
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
14
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
15
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

16
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

17
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

18
Sailboat Application

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

19
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

20
Precautions for Electronics

• Before a lightning storm
• After a lightning strike

21
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

22
Before Lightning Storm 2

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

23
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

24
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