lightning protection slide

Harger Lightning & Grounding © 2005

Lightning Protection System DesignLightning Protection System DesignHarger Lightning & Grounding

2005


Lightning Protection System Lightning Protection System DesignDesign

I. What is Lightning/Lightning Protection?II. Basic Principles of Lightning ProtectionIII. Applicable Codes/Standards IV. Lightning Protection Design BasicsV. “Zone of Protection”VI. Basic ComponentsVII. “ Typical ” Roof Top Detail VIII. Inspections


I. What is Lightning?

Consider Lightning a Gigantic Electrical Spark traveling betweenConsider Lightning a Gigantic Electrical Spark traveling betweenCloud to Cloud or Cloud to Earth containing an average Charge ofCloud to Cloud or Cloud to Earth containing an average Charge of30 to 50 Million Volts and a Current of 18,000 Amps.30 to 50 Million Volts and a Current of 18,000 Amps.



Lightning Damage Can Be Traced ToLightning Damage Can Be Traced To

Inadequate (or no) direct strike protection


Risks Posed from a Direct Strike



Risks Posed from an Indirect StrikeRisks Posed from an Indirect Strike



What is Lightning Protection?What is Lightning Protection?

NFPA 780 NFPA 780 --

A Complete System of Air Terminals, Conductors, Ground Terminals, Interconnecting Conductors, Surge Suppression Devices, and other Connectors or Fittings required to complete the System.


What is What is notnot Lightning Protection?Lightning Protection?

Early Streamer Emission – ESERadioactivePulsed VoltageSparking – Controlled Leader Trigger (CLT)

Lightning EliminationDissipation Array Systems (DAS)Charge Transfer Systems (CTS)


Non Conventional Lightning Protection SystemsNon Conventional Lightning Protection Systems

These systems are not allowed by:

US National Fire Protection Association (NFPA)IEEEIECUS MilitaryUnderwriters Laboratory (UL)


II. Basic Principles of Lightning ProtectionII. Basic Principles of Lightning Protection

Intercept the Lightning DischargeSafely Conduct the Lightning CurrentsDissipate the Lightning Currents in the EarthMinimize the Effects of Lightning Currents

Proper Bonding & routing of down-conductorsSurge Suppression

Protect incoming power circuitsProtect incoming telephone/data circuits


III. Applicable Codes/StandardsIII. Applicable Codes/Standards

NFPA 780NFPA 780UL 96AUL 96AUL 96UL 96


NFPA 780NFPA 780

Standard for the Installation of Lightning Protection Systems (2004)Most Active Standard AvailableNot a Code, (not enforced)


UL 96 & 96AUL 96 & 96A

UL96A - Installation Standard“Master Label”Independent Third Party Testing

UL96 - Manufacturing Standard for Listed LP Components


UL Master Label ProgramUL Master Label Program

Must be UL Listed to be Eligible

Materials must be UL Listed

System will be subjected to Inspection by UL


UL Master Label ProgramUL Master Label Program


IV. Lightning Protection Design Basics


NFPA 780NFPA 780Standard for the Installation of Lightning Protection SystemsStandard for the Installation of Lightning Protection Systems

2004 Edition2004 Edition

Chapter 3 Protection for Ordinary Structures

3-6 Strike Termination Devices. Strike termination devices shall be provided for all parts of a structure that are likely to be damaged by direct lightning flashes. Metal parts of a structure that are exposed to direct lightning flashes and that have a metal thickness of 3/16 in. (4.8 mm) or greater shall only require connection to the lightning protection system. Such connections shall provide a minimum of two paths to ground. Strike termination devices shall not be required for those parts of a structure located within a zone of protection.



ContinuedContinued……

3-6.1 Air Terminal Height. The tip of an air terminal shall be not less than 10 in. (254mm) above the object or area it is to protect. (See figure 3-6.1.)

Figure 3-6.1 Air terminal height.A: 10 in. (254 mm). See 3-6.1.

24 in. (600 mm). See 3-6.2.




3-6.2 Air Terminal Support. Air terminals shall be secured against overturning by attachment to the object to be protected or by means of braces that shall be permanently and rigidly attached to the building. An air terminal exceeding 24 in. (600 mm) in height shall be supported at a point not less than one-half its height.




3-8.1 Strike termination devices shall be placed at or within 2 ft (0.6m) of ridge ends on pitched roofs or at edges and outside corners of flat or gently sloping roofs.

Strike termination devices shall be placed on ridges of pitched roofs and around the perimeter of flat or gently sloping roofs at intervals not exceeding 20 ft (6m).




3-8.1 Strike termination devices 24 in. (600mm) or more above the object or area to be protected shall be permitted to be placed at intervals not exceeding 25 ft (7.6m).




3-8.1.2 Flat or Gently Sloping Roof Area. Flat or gently sloping roofs that exceed 50 ft (15m) in width or length shall have additional strike termination devices located at intervals not to exceed 50 ft (15m) on the flat or gently sloping areas.


Down Conductor PlacementDown Conductor Placement

Minimum of two per structureOne per every 100’ of perimeterAverage spacing will not exceed 100’




3-9.5 Conductor Bends. No bend of a conductor shall form an included angle of less than 90 degrees, nor shall it have a radius of bend less than 8 in. (203mm).




3-13 Ground Terminals.Each down conductor shall terminate at a ground terminal dedicated to the lightning protection system. The design, size, depth, and number of ground terminals used shall comply with 3-13.1 through 3-13.4.




Connections to Building SteelConnections to Building Steel

Clean to base metalBonding plates 8 in2

minimum contact areaWeldedBrazed


V. Zone of ProtectionV. Zone of Protection

A Zone of Protection is the space adjacent to a lightning protection system that is substantially immune to direct lightning discharges. This can be determined using the Rolling Sphere Method.


Rolling Sphere MethodRolling Sphere Method

3-7.3 Rolling Sphere Model.3-7.3.1 The zone of protection shall include the space not intruded by a rolling sphere having a radius of 150 ft (46 m). When the sphere is tangent to earth and resting against a strike termination device, all space in the vertical plane between the two points of contact and under the sphere are in the zone of protection.


Rolling Sphere Method

A zone of protection is also formed when such a sphere is resting on two or more strike termination devices and shall include the space in the vertical plane under the sphere and between those devices, as shown in Figure 3-7.3.1.

All possible placements of the sphere must be considered when determining the zone of protection using the rolling sphere model.


Rolling Sphere MethodRolling Sphere Method


Rolling Sphere Formula

d = eh1(300 – h1) - e h2(300 – h2)

where:

d = horizontal distance (ft)h1 = height of the higher roof (ft)h2 = height of the lower roof (top of the object) (ft)

h2

h1

d


Rolling Sphere Formula

Use of this formula is based on a 150 ft.(46-m) striking distance. For the formula to be valid, the sphere must be tangent to either the lower roof or in contact with the earth, and in contact with the vertical side of the higher portion of the structure. In addition, the difference in height between the upper and lower roof or earth must be 150’ or less.

For Example...For Example...

d

h2

h1

h1= 100’

h2 = 50’

d = 20’

Is the lower roof in the zone of protection?


For Example...For Example...

d = 100(300 – 100) - 50(300 – 50)

-20000 12500d =

d = 141.42 - 111.80

d = 29.62’



Rolling Sphere FormulaRolling Sphere Formula


VII. Basic Components

Air TerminalsLightning ConductorsGround TerminalsConnectors/FittingsSurge Suppression Devices


Types of Air Terminals

Plain Air TerminalsSafety Air TerminalsFlexible Air Terminals


Types of Lightning ConductorsTypes of Lightning Conductors

UL Listed Lightning Conductors

Copper Aluminum

Class I Class II

Structural Steel Framework


Types of Ground TerminalsTypes of Ground Terminals

Ground Rods

Plain/Sectional Copper-Clad Steel, Copper, Galvanized Steel, Stainless Steel

Enhanced Ground Rods


Types of Ground TerminalsTypes of Ground TerminalsContinued...Continued...

Ground PlatesGround MeshConcrete Encased Electrodes

Reinforcing SteelCopper Conductors


Connectors/FittingsConnectors/FittingsFunctionsFunctions

Bonds Conductors to Strike Terminals and Ground Terminals Bond Metal Bodies to Provide a Path to GroundAlleviates Potential Differences between System and Metal Bodies Helps Prevent Flashover Potentials


Surge Suppression DevicesSurge Suppression Devices

Helps Prevent Surge Currentsfrom Entering the Structure via Electrical, Data, Phone, Cable Lines, etc.

Integral Part of TotalProtection Package

UL96A & NFPA SurgeSuppression Requirements vague

Roof Top Detail

VIII.


Details


IX. Inspection and MaintenanceIX. Inspection and Maintenance

Inspection after Installation - UL Master Label

Ongoing Inspection -NFPA 780 Appendix B Recommends Periodic (Annual) Inspections

Thank You


lightning protection slide

Documents

lightning dischargesafely

lightning currentsdissipate

notnot lightning protection

lightninglightning protection

ul listedsystem

basic componentsvii

gigantic electrical

applicable codesstandardsnfpa