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ERITECH

Lightning ProtectionHandbook

Designing to the IEC 62305 Series

of Lightning Protection Standards

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Lightning Protection Consultant Handbook

ERICO is dedicated to providing a cost-eective lightning protection solution or any given application. ERICO manuactures,using the ERITECH trade name, lightning protection systems in ull accordance with more than twelve national and international

standards, as well as non-conventional systems or applications where these provide an advantageous solution or the customer.

ERICO operates in every region o the world and supports the global market with an extensive distribution network to help ensurethat our products and expertise are available or any project, regardless o size or location.

Founded in 1903 as the Electric Railway Improvement Company, ERICO developed the CADWELD exothermic welding process in1936. During the 1970s, ERICO pioneered the development and standardization o the copper bonded steel earthing electrode.

Since that time, ERICO has developed novel lightning protection solutions and introduced new manuacturing processes to improvetraditional lightning protection hardware.

NOTE IEC and national standards continue to evolve. This handbook was written with reerence to the current editions o thesestandards as o 2009.

WARNINGERICO products shall be installed and used only as indicated in ERICOs product instruction sheets and training materials. Instruction sheets are available at www.erico.comand rom your ERICO customer service representative. Improper installation, misuse, misapplication or other ailure to completely ollow ERICOs instructions and warningsmay cause product malunction, property damage, serious bodily injury and death.

WARRANTY

ERICO products are warranted to be ree rom deects in material and workmanship at the time o shipment. NO OTHER WARRANTY, WHETHER EXPRESS OR IMPLIED(INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE), SHALL EXIST IN CONNECTION WITH THE SALE OR USE OF ANY ERICOPRODUCTS. Claims or errors, shortages, deects or nonconormities ascertainable upon inspection must be made in writing within 5 days ater Buyer's receipt o products.All other claims must be made in writing to ERICO within 6 months rom the date o shipment or transport. Products claimed to be nonconorming or deective must,upon ERICO's prior written approval in accordance with its standard terms and procedures governing returns, promptly be returned to ERICO or inspection. Claims notmade as provided above and within the applicable time period will be barred. ERICO shall in no event be responsible i the products have not been stored or used inaccordance with its specications and recommended procedures. ERICO will, at its option, either repair or replace nonconorming or deective products or which it isresponsible or return the purchase price to the Buyer. THE FOREGOING STATES BUYERS EXCLUSIVE REMEDY FOR ANY BREACH OF ERICO WARRANTY AND FOR ANYCLAIM, WHETHER SOUNDING IN CONTRACT, TORT OR NEGLIGENCE, FOR LOSS OR INJURY CAUSED BY THE SALE OR USE OF ANY PRODUCT.

LIMITATION OF LIABILITYERICO excludes all liability except such liability that is directly attributable to the willul or gross negligence o ERICO's employees. Should ERICO be held liable its liabilityshall in no event exceed the total purchase price under the contract. ERICO SHALL IN NO EVENT BE RESPONSIBLE FOR ANY LOSS OF BUSINESS OR PROFITS, DOWNTIMEOR DELAY, LABOR, REPAIR OR MATERIAL COSTS OR ANY SIMILAR OR DISSIMILAR CONSEQUENTIAL LOSS OR DAMAGE INCURRED BY BUYER.

IntroductionThis handbook is written to assist in the understanding o the IEC 62305 series o lightning protection standards. This guidesimplies and summarizes the key points o the standards or typical structures, and as such, the ull standards should be

reerred to or nal verication. This handbook does not document all IEC requirements, especially those applicable to lesscommon or high risk structures such as those with thatched roos or containing explosive materials. In many situations there

are multiple methods available to achieve the same end result; this document oers ERICOs interpretation o the standardsand our recommended approach. In order to provide practical advice, inormation is included on industry accepted practices

and rom other standards.

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Key Terms and Abbreviations

Term Denition

Air-Termination

Part o the lightning protection system to intercept the lightning fash (strike). For example,

an air-terminal providing a protection angle to protected equipment, or horizontal or verticalconductor providing protection via the mesh method

British Standards (BS) Body responsible or implementation o national British standards, identied by BS prex

CENELECEuropean Committee or Electrotechnical Standardisation (essentially European standard or Norm,

identied by EN or NE prex)

Class (o LPS)Classication o lightning protection system. Class I, II, III, IV relate to the lightning protection level

and dene, or example, the dierent rolling sphere diameters to be used

Earth electrodesThose parts o the earth termination system in direct contact with the earth, such as ground rods,

buried wires, oundation earthing, etc

Earth-termination Part o the external LPS to dissipate lightning current into the earth

External lightningprotection system

Air-termination(s), down-conductor(s) and earth termination(s)

Internal lightningprotection system

Equipotential bonding and/or electrical isolation o the external LPS rom internal conductiveelements

IEC International Electrotechnical Commission, responsible or ormation o International Standards

Lightning protectionlevel (LPL)

Number assigned to represent maximum and minimum lightning parameters that should not beexceeded by natural lightning

Lightning protectionsystem (LPS)

Complete system or lightning protection o structure. Includes internal and external lightningprotection measures

Lightning protection zone(LPZ)

Zone where lightning electromagnetic environment is dened

Mesh method (MM) Method to determine position o air-termination system

Protection angle method

(PAM)Method to determine position o air-termination system

Rolling sphere method(RSM)

Method to determine position o air-termination system

Separation distance Distance between two conductive parts where no dangerous sparking (fashover) can occur

Services

Circuits and pipes, etc, entering into structure rom external environment. Typically phone,

power, TV, gas, water, sewerage systems, etc

Surge protective device

(SPD)Device or protecting electrical/electronic equipment rom transient voltage damage

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Table of Contents

1. IEC and EN Standards 6

1.1 IEC 62305 series

1.2 EN 50164 series

1.3 Normative and inormative

1.4 IEC terminology

6

6

8

8

2. Theory o the lightning fash 9

2.1 The thundercloud

2.2 Mechanics o the lightning strike

2.3 Lightning parameters

2.4 Lightning damage and risk management

10

10

11

13

3. Introduction to protection methods and risks 14

3.1 Risks 15

4. Risk management 17

4.1 Overview o risk analysis 17

5. Lightning protection zones 22

6. Design process 23

7. Material requirements 24

7.1 Copper versus aluminum

7.2 Use o dissimilar metals

7.3 PVC covered and concealed conductors

7.4 Tape, versus solid round, versus stranded

24

25

27

27

8. Natural components 28

8.1 Metallic acades, proles, rails, etc

8.2 Use o steelwork

8.3 Use o rebar in reinorced concrete

28

28

28

9. Design methods 33

9.1 Rolling sphere

9.2 Mesh method

9.3 Protection angle method

35

37

39

10. Air-terminations 43

10.1 Recommendation on positioning

10.2 Masts and antennas10.3 Protection o other items protruding above the roo

10.4 Bonding o roo top xtures

10.5 Expansion joints and roo penetrations

44

4545

48

48

11. Down-conductors 49

11.1 Down-conductors or isolated and non-isolated LPS

11.2 Down-conductor routing

11.3 Fixing o down-conductors

50

50

51

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Table of Contents (continued)

12. Bonding and separation distances 52

12.1 Bonding o services and external conductive parts

12.2 Separation distance requirements

12.3 Bonding o internal metallic items and other services

52

53

54

13. ERITECH

Isolated Down-conductor 5513.1 Telecommunications applications

13.2 Other applications

13.3 Isolated Down-conductor design

55

56

56

14. Earthing 57

14.1 Earthing resistance requirements

14.2 Type A vertical and horizontal electrodes

14.3 Type B ring electrode

14.4 Comparison o Type A and Type B arrangements

14.5 Foundation earth electrodes

14.6 Special earthing measures

14.7 General earthing advice

57

58

59

60

60

61

62

15. Inspection and testing 66

16. Special situations 67

16.1 Tall buildings 67

17. Surge protective devices or low-voltage power distribution systems 68

17.1 Surge Protection Devices and Transient Voltages

17.2 General procedure or SPD selection and installation

17.3 General inormation and terms

17.4 SPD requirements or acilities with lightning protection system17.5 SPD requirements or acilities without lightning protection system

17.6 Secondary SPD requirements

17.7 Selection and connection conguration or common power distribution system types

17.8 Other installation requirements

17.9 High risk situations

68

71

72

7377

77

79

83

86

18. Surge protective devices or telecommunications and signalling services 87

19. Other surge protective device applications 88

20. British Standard BS 6651 and EN/IEC standards 89

20.1 BS 6651-1991 compared to BS EN 62305

20.2 BS EN 62305-2 compared to IEC/EN 62305-2

89

90

21. IEC design standard and EN component standard conficts 91

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1. IEC and EN Standards

The specication o a lightning protection system should require that the design complies with the IEC 62305 series o designstandards and that materials comply with the EN 50164 series o component standards.

The International Electrotechnical Commission (IEC) is a body

responsible or implementing international standards. Its technical

committees are comprised o representatives rom variousmember national standards, where each country is entitled to onevote during the process o creation and issuing the standard. The

standards generally have an IEC prex to their number (CEI orFrench versions). IEC standards are produced in English and French

languages. For most countries the adoption o these standards isvoluntary, and oten selected content o the standard is absorbed

and introduced as improvements to that countrys own standard.

Also, within Europe, there exists the European Committee

or Electrotechnical Standardisation (CENELEC). The membercountries currently include Austria, Belgium, Cyprus, the Czech

Republic, Denmark, Estonia, Finland, France, Greece, Hungary,

Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, theNetherlands, Norway, Poland, Romania, Slovakia, Slovenia, Spain,Sweden, Switzerland and the United Kingdom. IEC and CENELEC

generally work in parallel, and CENELEC members vote to adoptnew IEC standards as CENELEC standards. The committees o

CENELEC may choose to make some alterations to the IEC version.Additionally, CENELEC produce their own standards to which

IEC have no counterpart. CENELEC documents are produced inEnglish, French and German and an approved CENELEC standard

will have an EN prex (or NE in the French language versions).

The important act with CENELEC standards is that by rule themember countries are bound to adopt all CENELEC standards as

national standards. In the process o adopting these standards,

minimum changes are permitted. In-country clauses (exceptionsor changes) can only be made under very strict circumstances.When such standards are adopted at the national level, any

conficting national standard must be withdrawn (an overlapperiod is permitted).

For the EN IEC 62305 series o lightning protection standards,each member country has introduced these at a national level by

November 2006 and has withdrawn any conficting standardsby February 2009.

At each level (International, European, National) a dierentnaming prex convention is used For example:

IEC62305-1(IECversion) EN62305-1(CENELECadoptedcopyoftheabove)

BSEN62305-1(BritishNationalStandardadoptionofthe above)

This document ocuses upon the IEC/EN standards and, or aspecic design, the applicable national standards should be

reerred to in order to ascertain i dierences exist.

Reerence in this document is given to standards being either

design or component standards. Design standards are those usedby the lightning protection designer or installer to determine

the type and placement o the lightning protection system.Component standards are those used by the manuacturer o

the lightning protection hardware (components) to ensure thehardware is o adequate specication and quality.

1.1. IEC 62305 series

The IEC 62305 series o standards are primarily design standards,

giving the user a tool kit o rules and options to provide lightningprotection or a structure. The standards cover structure protection

and equipment protection with regard to the eects o direct andindirect lightning fashes.

While the IEC 62305 series o standards introduces many newaspects, it is predominantly a European harmonization o the

various supporting country lightning protection standards.

IEC 62305 Protection Against Lightning is comprised o 4 parts

(documents):

IEC62305-1Part1:GeneralPrinciples

IEC62305-2Part2:RiskManagement IEC62305-3Part3:PhysicalDamagetoStructureand

Lie Hazard IEC62305-4Part4:ElectricalandElectronicSystems

within Structures IEC62305-5Part5:Services(Thispartwasnotintroduced)

IEC 62305 series o standards expands, updates and replaces the

earlier IEC 1024-1-1 (1993) & IEC 1024-1-2 (1998), IEC 61622(1995 & 1996), IEC 61312-1 (1995), IEC 61312-2 (1998), IEC61312-3 (2000) & IEC 61312-4 (1998).

Since the IEC 62305 series was parallel approved as a CENELECstandard, the EN version is identical to the IEC version. As a

CENELEC standard this means that the EN 62305 standards havereplaced the various country source standards, such as BS 6651,

NFC 17-100 and DIN VDE 0185.

1.2. EN 50164 series

Within Europe, the CENELEC has released the EN 50164 series

o standards. The EN 50164 series are component standards towhich the manuacturers and suppliers o lightning protectioncomponents should test their products to veriy design and quality.

The EN 50164 series currently comprises o:

EN 50164-1 Lightning protection components (LPC)

Part 1: Requirements or connection components EN 50164-2 Lightning protection components (LPC)

Part 2: Requirements or conductors and earth electrodes EN 50164-3 Lightning protection components (LPC)

Part 3: Requirements or isolating spark gaps EN 50164-4: Lightning Protection Components (LPC)

Part 4: Requirements or conductor asteners

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1. IEC and EN Standards (continued)

EN50164-5:LightningProtectionComponents(LPC)

Part5:Requirementsforearthelectrodeinspectionhousings andearthelectrodeseals

EN50164-6:LightningProtectionComponents(LPC) Part6:Requirementsforlightningstrikecounters

EN50164-7:LightningProtectionComponents(LPC) Part7:Requirementsforearthingenhancingcompounds

ThisseriesofstandardsiscurrentlybeingpublishedatIEClevelunderthenameIEC62561series.

TheEN50164seriesofstandardsaregenerallycomponent

standardstowhichthesupplieroftheequipmentshouldhavetestedtheirproducts.ERICOhascompletedanextensive

regimeoftestingtothesestandards,anddetailsareavailableuponrequest.

EN50164-1scopecoversconnectioncomponentssuchasconnectors,bondingandbridgingcomponentsandexpansion

piecesaswellastestjoints.Theintentofthisstandardisthatanymechanicalconnectionbetweenthetipoftheair-terminalandthe

bottomoftheearthelectrodeshouldbetested.Thiscoversthemoreobviousdown-conductorconnectors(cross-overconnectors,

tapeclamps,etc)anddown-conductortestlinks,tothelessobviousair-terminal(rod)toair-terminalbaseconnectionand

down-conductortoearthelectrodeconnection.

EN50164-1testingclassiestheproductsaccordingtotheir

capabilitytowithstandlightningcurrentbyanelectricaltest:

ClassHHeavyDuty(testedwith100kA10/350s),or ClassNNormalduty(testedwith50kA10/350s)

Standard Title Type

IEC 62305-1

(EN 62305-1)ProtectionagainstlightningPart1:Generalprinciples DesignStandard

IEC 62305-2

(EN 62305-2)ProtectionagainstlightningPart2:RiskManagement DesignStandard

IEC 62305-3

(EN 62305-3)ProtectionagainstlightningPart3:PhysicalDamagetoStructureandLifeHazard DesignStandard

IEC 62305-4

(EN 62305-4)ProtectionagainstlightningPart4:ElectricalandElectronicSystemswithinStructures DesignStandard

EN 50164-1 Lightningprotectioncomponents(LPC)Part1:Requirementsforconnectioncomponents ComponentStandard

EN 50164-2 Lightningprotectioncomponents(LPC)Part2:Requirementsforconductorsandearthelectrodes ComponentStandard

EN 50164-3 Lightningprotectioncomponents(LPC)Part3:Requirementsforisolatingsparkgaps ComponentStandard

EN 50164-4 Lightningprotectioncomponents(LPC)Part4:Requirementsforconductorfasteners ComponentStandard

EN 50164-5Lightningprotectioncomponents(LPC)Part5:Requirementsforearthelectrodeinspection

housingsandearthelectrodesealsComponentStandard

EN 50164-6 Lightningprotectioncomponents(LPC)Part6:Requirementsforlightningstrikecounters ComponentStandard

EN 50164-7 Lightningprotectioncomponents(LPC)Part7:Requirementsforearthingenhancingcompounds ComponentStandard

Main IEC and EN standards relating to design and testing o lightning protection systems/components.Table 1.

Andaccordingtoitsinstallationlocationbyenvironmentaltest:

Aboveground(saltmist&sulphurousatmospheretests),and Buriedinground(chlorideandsulphatesolutiontest)

EN50164-2scopecoversmetallicconductors,down-conductors(otherthannaturalconductorssuchasbuildingreinforcing

steel)andearthelectrodes.Itshouldbenotedthatthemetallicconductorrequirementalsocoverstheair-terminals(rods).The

testsincludemeasurementstoconrmcompliancewithminimum

sizerequirements,resistivityandenvironmentaltesting.Earthelectrodesaresubjectedtotestsincludingbendtests,adhesion

tests,andenvironmentaltests.Coupledearthelectrodesandthecouplingdevicearealsosubjectedtohammercompression

(impacttesting)andtherequirementsofIEC62305-1.

EN50164-3scopecoversisolatingsparkgapsusedinlightning

protectionsystems,suchasthoseusedtobondmetalworktoalightningprotectionsystemwheredirectconnectionisnot

permissibleforfunctionalreasons.

EN50164-4scopecoverstestsproceduresandrequirementsformetallicandnon-metallicfastenersusedonmost(butnotall)

wallandroofmaterialstosecureairterminationsystemsand

downconductors.Fastenersusedinexplosiveatmospheresshouldbe

subjectedtoadditionalrequirementsnotdenedinthisstandard.

EN50164-5scopecoversrequirementsandtestsforearthpits

andearthsealsmadeofsteel,plastic,concreteamongothers.Load-bearingcapacitytestsandsealqualitytestsarethekeytests

coveredinthestandard.

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1. IEC and EN Standards (continued)

Term Denition

Lightning strokeSingle electrical discharge in a lightningfash to earth. The lightning fash mayhave multiple strokes

Lightning fashElectrical discharge o atmospheric origin

between cloud and earth consisting oone or more strokes

Multiple strokeA lightning fash where more than onestroke (electrical discharge) occurs

Point o strokePoint where lightning fash strikesearth/object

Lightning current Current fowing at point o strike

Main IEC terms associated with the lightning event.Table 2.

Lightning is a common event. At any one time, there are some1700 electrical storms active throughout the world, producing in

excess o 100 fashes per second. This equates to an aggregateo some 7 to 8 million fashes per day. O these, approximately

90% are cloud-to-cloud fashes and the remaining arepredominately cloud-to-ground fashes. Tropical regions o the

world have particularly high incidences o lightning as depictedby isokeraunic thunder day maps.

Common Terminology IEC Terminology

Lightning strike Lightning fash

Discharge current Lightning current

Common non-IEC terminology.Table 3.

EN 50164-6 scope covers test procedures and requirements or

lightning strikes counters used in lightning protection systemsbut also in surge protection systems. Mechanical, electrical and

corrosion tests are described in this standard and electromagneticcompatibility is also addressed.

EN 50164-7 scope covers the requirements and tests or earth

enhancing compounds used to increase the contact surace areao earth electrodes. Rell materials are not part o this standard.Among the tests included in the standard are conductivity

tests, chemical tests (pH, solubility in acid environments), andcomposition tests (sulur).

At this time, while EN 50164-1, EN 50164-2 and EN 50164-3are CENELEC standards and thus compliance is required, the

IEC 62305 series do not ully reer to these standards. That is tosay, while you must use EN 50164-1/2/3 approved components,

IEC/EN 62305 series, or example, does not actually speciy orwhich circumstances EN 50164-1 Class H or Class N materials

are required. It is strongly recommended that Class H be used

in all applications, but with Class N devices being permitted orbonding to items not subject to the ull lightning current.

It should also be known that there are some small dierencesbetween the material requirements o the EN component

standards and the material specications in the IEC designstandards, such as minimum conductor sizes and tolerance.

Thereore it is possible or example, to have a conductor thatmeets the requirements o design standard IEC 62305-3, but not

the component standard EN 50164-2. Reer to Section 21 orurther inormation.

Manuacturers and suppliers o lightning protection components

should be able to provide test reports or each o their products

stating compliance to these standards. Importantly, theclassication (class and environment) should be stated togetherwith the scope o testing. Note that the approval is only valid or

the combinations o conductor sizes and congurations tested.For example, the approval is unlikely to be valid i the connector

is used with non-standard conductor sizes.

1.3. Normative and inormative

It should be understood that the main body o standards arenormative. That is, the requirements given are mandatory (unless

otherwise indicated in the text). At the rear o the standard,annexes provide additional support inormation and examples.

The annexes may be headed as normative or inormative. Anormative annex means any requirements are mandatory, while an

inormative annex is or inormation purposes and any containedrequirements are recommendations (i.e. non-mandatory).

To summarize earlier inormation, with the exception oCENELEC member countries, the requirements o IEC 62305

series, EN 50164 series, or a national version o one o thesedocuments is only mandatory i the country has specically

adopted the standard. Any local national standard will takeprecedence. For CENELEC member countries the standards

are mandatory with compliance being required to the nationalimplementation i existing, or otherwise the EN version.

1.4. IEC terminology

Where practical, this document uses IEC dened terms anddenitions. For example the term earthing is used in

preerence to grounding. Within the lightning protectionindustry there is oten indiscriminate use o incorrect terms

associated with the lightning event. The ollowing explains thepreerred terms.

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Header Goes Here2. Theory of the Lightning Flash

With increasingly complex and sophisticated buildings and equipment, a single lightning stroke can result in physical damage

and catastrophic ailure. It can initiate re, cause major ailures to electrical, telephone and computer services and simultaneouslycause substantial loss o revenue through down-time.

World thunder day map; note the high lightning density areas are regionalized around the equator.Figure 1.

EUROPE

AFRICA

AUSTRALIA

NORTH

AMERICA

ASIA

SOUTH

AMERICA

EQUATOR

THUNDERSTORM DAYS

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Header Goes Here

2.2. Mechanics o the lightning strike

The separation o electrical charge within a cloud allows electricpotentials to increase to a point where a neutralizing discharge

must occur. For lightning protection, we are mainly concernedabout the cloud-to-ground discharge. This is a two-staged

process, with one process being initiated rom the cloud, whilethe second is initiated rom the ground or structure.

Ionization occurs at the bottom o the cloud to orm coronadischarges. A leader initiates and begins to propagate towards

the ground. The presence o wind shear tends to blow away theionized air, halting the progression momentarily until sucient

ionization develops to cause breakdown and allow the dischargeto progress in the next discrete step. This stepped leader

progresses rapidly towards the ground and may branch intomany "ngers" in an attempt to reach ground.

As the leader approaches the ground, the electric eld rapidlyincreases, accelerating local ground ionization. At this point, the

potential dierence between the leader and the earth may beas great as 100 million volts, resulting in nal breakdown o the

air. The ground discharge begins to move up (upward leader)towards the downward leader, intercepting at some tens to

hundreds o meters above ground level.

6-12 km

1-6 km

Heavy, cold air mass Warm air mass

2.1. The thundercloud

Lightning is a natural phenomenon which develops when theupper atmosphere becomes unstable due to the convergence

o a warm, solar heated, vertical air column on the cooler upperair mass. These rising air currents carry water vapor which,

on meeting the cooler air, usually condense, giving rise toconvective storm activity. Pressure and temperature are such that

the vertical air movement becomes sel-sustaining, orming the

basis o a cumulonimbus cloud ormation with its center corecapable o rising to more than 15,000 meters.

To be capable o generating lightning, the cloud needs to be

3 to 4 km deep. The taller the cloud, the more requent thelightning. The centre column o the cumulonimbus can have

updrats exceeding 120 km/hr, creating intense turbulence withviolent wind shears and consequential danger to aircrat. This

same updrat gives rise to an electric charge separation whichultimately leads to the lightning fash. Figure 2 shows a typicalcharge distribution within a ully developed thunder cloud.

Lightning can also be produced by rontal storms where a

ront o cold air moves towards a mass o moist warm air. Thewarm air is lited, thus generating cumulonimbus clouds and

lightning in a similar mechanism to that described earlier. One

major dierentiation o this type o event is that the cold rontcan continue its movement and result in cumulonimbus cloudsspread over several kilometers width. The surace o the earth

is negatively charged and the lower atmosphere takes on anopposing positive space charge. As rain droplets carry charge

away rom the cloud to the earth, the storm cloud takes onthe characteristics o a dipole with the bottom o the cloud

negatively charged and the top o the cloud positively. It isknown rom waterall studies that ne precipitation acquires

a positive electrical charge. Larger particles acquire a negativecharge. The updrat o the cumulonimbus separates these

charges by carrying the ner or positive charges to highaltitudes. The heavier negative charges remain at the base o the

cloud giving rise to the observance that approximately 90% oall cloud-to-ground fashes occur between a negatively charged

cloud base and positively charged earth (i.e. negative lightning).

Approximately 90% o all lightning fashes are cloud-to-cloud

with the other 10% being cloud-to-ground fashes.

Ground-to-cloud fashes are extremely rare and generally only

occur rom high mountain tops or tall man-made structures they are typically positive strokes (positive lightning).Figure 2. Typical charge distribution in

cumulonimbus cloud.

Figure 3. Cumulonimbus cloudsgenerated by rontal storms.

2. Theory of the Lightning Flash (continued)

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Header Goes Here2. Theory of the Lightning Flash (continued)

Figure 4. The stepped leader progressingtowards earth.

Figure 5. Upward leader completes theionized channel.

Oncetheionizedchannelhasbeencompletedbythejunctionoftheupwardanddownwardleaders,alowimpedancepath

betweenthecloudandgroundexistsandthemainstrokecommences.Thisischaracterizedbyarapidlyincreasingelectric

currentwhoserateofriseistypically10kA/s.Peakcurrentsaveragingaround30kAaretypical,withminimumcurrents

beingafewkA.Maximumlightningcurrentsexceeding200kAhavebeenrecorded.

Itisalsopossibletohaveconsecutivestrokesdownthesame

channel.Thisoccurswhentheinitialdischargeneutralizesthelocalizedchargecellinthecloud.Nearbycloudcellsthenash

acrosstotheionizedchannelanduseittodischargetoground.Inthismanner,upto16strokeshavebeenobservedusingthe

onechannel.Thesemultiplestrokeswithintheonelightningasharesometimesreferredtoasre-strikes.

Theaverageenergyreleasedinalightningashis55kWhr,asignicantamountofenergybymoderngenerationstandards.

Thedangerofthelightningcurrentliesinthefactthatalltheenergyisexpendedinonly100to300microsecondsand

thatthepeaklightningcurrentisreachedinonly1to2microseconds.

Thedifferencebetweenpositiveandnegativelightningisthattheleaderinthecaseofpositivelightningisgenerallynot

steppedandtherearerarelymultiplestrokes.Thereistypicallyonlyonereturnstroke,afterwhichacontinuouscurrentows

todischargethecloud.

2.3. Lightning parameters

Lightningisanaturalphenomenonwhere,forthepurposeofanalysisanddesign,astatisticalapproachistaken.Data

fromInternationalCouncilofLargeElectricalSystems(CIGRE)indicatesthat:

5%ofrst,negativelightningstrokesexceed90kA(averageis33kA)

5%ofpositivelightningstrokesexceed250kA(averageis34kA)

5%ofnegativesubsequentstrokesexceedarateofcurrentriseof161kA/s

IntheIEC62305series,fourlightningprotectionlevelsareintroducedandthedesignrulesarebasedontheLPSbeing

abletoprotectagainstmaximumvalues(sizingefciency)andminimumvalues(interceptionefciency)ofcurrent.LPLI

offersthehighestprotectionlevel(greatestlevelofprotection),withLPLIVofferingthelowestlevelofprotection.

Table 4indicatesfortheselightningprotectionlevelsthe

maximumcurrentexpectedandtheprobabilitythatthismaybeexceeded.Thestandardensuresthatair-termination,conductor

andearthterminationsizearesufcienttowithstandtheexpectedmaximumcurrent.

LPL I LPL II LPL III LPL IV

Maximumpeakcurrent(kA10/350s) 200 150 100 100

Probabilitycurrentisgreater(%) 1 2 3 3

Maximum current levels (related to sizing efciency) or lightning protection levels I to IV and probability o exceedingTable 4.these levels.

Stepped leader movesprogressively from cloudto ground and can followone or several paths.

Strikin

g

dis

tance

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Minimumcurrent(kA) 3 5 10 16

Probabilitycurrentisgreaterthanminimum(%)

99 97 91 84

Rollingsphereradius(m) 20 30 45 60

Minimum current levels (related to interceptionTable 5.

efciency) or lightning protection levels I to IV.

10 s

350 s

50%

10%

90%

t

100%

(+ve)

Ground

Strikingdistance

Respondingupward leader

Downwardleader

(-ve)r = 10 Ip0.65

r20 m

44 m

91 m

200 m

I p3 kA

10 kA

30 kA

100 kA

Figure 6. Waveshape.

Figure 7. Striking Distance.

Thelowerlightningprotectionlevels(LPL II, III & IV)eachincreasetheair-terminalspacing,reducingtheirabilitytocapture

smallerlightningashes,thusreducingoverallthepercentageoflightningeventstheycanprotectagainst.

Table 5alsodetailstherollingsphereradiususedintherolling

spheredesignmethod.Therollingspheremethodisthepreferredmethodfordeterminingpositioningofair-terminals

(protectionanglemethodandmeshmethodaredescribedlater).Theradiusofthesphereisequaltothestrikingdistance(using

earlierformula)associatedwiththeminimumcurrentlevelfor

thechosenlightningprotectionlevel.Thisimaginarysphereisrolledoverthestructure.Thesurfacecontactpointstracedoutbythespheredenepossiblepointsthatmaylaunchanupward

leadertointerceptwiththedownwardleader.Allthesepointsaredeemedtorequireprotection,whilsttheuntouchedpoints

donot.Generallyalightningprotectionsystemisdesignedsuchthattherollingsphereonlytouchesthelightningprotection

systemandnotthestructure.

TofurtherexplainTable 5,alightningprotectionsystemto

provideLPLIV,designedusingtherollingspheremethod,woulduseair-terminalsplacedusingarollingsphereradiusof60m.

Whiletheactualwaveshapeofthelightningcurrentvariesfromeventtoevent,researchshowsthatastatisticalprobabilitycan

bedeterminedforoccurrenceofagivenwaveshape.ForthepurposeofsimplicationthemaximumvaluesinTable 4are

speciedusinga10/350swaveshape.AsshowninFigure 6,fora10/350seventthefronttime(alsoknownasrisetime)is

10sdurationandthetimetodecayto50%is350s.

Forair-terminalplacement,themainconsiderationisthe

minimumvalueofexpectedcurrentandtheabilityofthelightningprotectionsystemtointerceptthesesmallerashes.

Asnotedearlier,asthelightningdownwardleaderapproachesthegroundorstructure,theelectriceldincreasestothepoint

thatthegroundorstructurelaunchesanupwardleaderthatmayeventuallyinterceptthedownwardleader.Thisistermed

thestrikingdistance.Thelargertheamountofchargecarriedbythelightningleader,thegreaterwillbethedistanceatwhich

thishappens.Thelargerthechargeoftheleader,thelargertheresultinglightningcurrent.Itisgenerallyacceptedthat

thestrikingdistancerisgivenby:

r= 10I0.65

WhereIisthepeakcurrentoftheresultingstroke.

Thisformulashowsthatitismoredifcultforanair-terminal

tointerceptasmallerlightningashthanalargerash,asthesmallerashmustapproachclosertotheair-terminalbefore

theupwardleaderislaunched.Toprotectthestructureagainstsmallerlightningashes,air-terminalsmustbespacedcloser

together.Forsmallerlightningashesthereisariskthatanair-terminalmaynotbecloseenoughtointerceptthedownleader,

thusacloserstructuralpointreleasesanupwardleaderwhichinterceptstheash(i.e.thebuildingisstruck).

Foreachofthelightningprotectionlevels,aminimumcurrentleveltobeprotectedagainsthasbeendetermined(selected).

Table 5detailsthesecurrentlevels,togetherwithprobabilitypercentagesthatlightningmaybegreaterthantheselevels.For

example,LPLIpositionsterminalssuchthat99%ofalllightningashesareintercepted(allthoseof3kAorgreater).Thereisonly

a1%probabilitythatlightningmaybesmallerthanthe3kAminimum,andmaynotbecloseenoughtoanair-terminaltobe

intercepted.Itshouldbenotedthatashesoflessthan3kAarerare,andtypicallywouldnotbeexpectedtocausedamageto

thestructure.ProtectiongreaterthanLPLI(99%)wouldrequiresignicantlymorematerial,isnotcoveredbythestandardand

generallyisnotrequiredforcommercialconstruction.

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These air-terminals would be positioned such that they would

capture all lightning fashes o 16 kA or greater, thus oeringprotection to at least 84% o the lightning (the term at least is

used to indicate that the percentage o lightning captured mightbe greater, since smaller lightning fashes could be captured i

they were closer to the air-terminal). To oer a greater lightningprotection level (e.g. LPL I, II or III) a smaller rolling sphereradius would be used. This would result in a reduced spacingbetween air-terminals (more air-terminals), thus positioning the

air-terminals to capture smaller lightning fashes, and increasingthe total percentage o lightning fashes captured.

2.4. Lightning damage & risk management

No lightning protection system is 100% eective. A systemdesigned in compliance with the standard does not guarantee

immunity rom damage. Lightning protection is an issue ostatistical probabilities and risk management. A system designed

in compliance with the standard should statistically reduce therisk to below a pre-determined threshold. The IEC 62305-2 risk

management process provides a ramework or this analysis.

An eective lightning protection system needs to control a

variety o risks. While the current o the lightning fash createsa number o electrical hazards, thermal and mechanical hazards

also need to be addressed.

Risk to persons (and animals) include:

Directash

Steppotential

Touchpotential

Sideash

Secondaryeffects:

asphyxiation rom smoke or injury due to re

structural dangers such as alling masonry rompoint o strike

unsae conditions such as water ingress rom roopenetrations causing electrical or other hazards,

ailure or malunction o processes, equipment andsaety systems

Risk to structures & internal equipment include:

Fireand/orexplosiontriggeredbyheatoflightningash,its attachment point or electrical arcing o lightning

current within structures

Fireand/orexplosiontriggeredbyohmicheatingof

conductors or arcing due to melted conductors

Puncturesofstructureroongduetoplasmaheat

at lightning point o strike

Failureofinternalelectricalandelectronicsystems

Mechanicaldamageincludingdislodgedmaterialsat

point o strike

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Header Goes Here

SeparationDistance

Internal

Earth-terminationSystem

Service

entrancebox

Foundation earthing electrode

Equipotential bonding for heating,air-conditioning, and sanitation

SPD for AC services

SPD fortelephone line

Down-conductorSystem

Figure 8. External and internal lightning protection system.

3. Introduction to Protection Methods & Risks

The design o a lightning protection system needs to:

Intercept lightning fash (i.e. create a preerred pointo strike)

Conduct the lightning current to earth

Dissipate current into the earth

Create an equipotential bond to prevent hazardouspotential dierences between LPS, structure and

internal elements/circuits

3. Introduction to protection methodsand risks

The inancy o the science o lightning protection is best

attributed to Benjamin Franklin. The story o his kite fyingexperiment to prove that lightning was the same type o

electricity as that stored in a Leyden jar, is well documentedand has become a modern day legend. The rst mention o the

traditional lightning rod was published by Franklin in 1750 in

Gentlemans Magasine [sic]and then later in his treatises on thesubject published in 1751. In this he recommends the use olightning rods to ... Secure houses, etc, rom Lightning.

In 1876, Franklins research was taken urther by James ClerkMaxwell who suggested that by completely enclosing a building

with metal cladding, lightning current would be constrained tothe exterior o the building and no current would fow within

the building itsel. This concept has given rise to a relativelymore cost eective approach known as the Faraday Cage (mesh

method), in which a matrix o conductors is used to orm an

equipotential cage around the structure to be protected.

In achieving this the lightning protection system must:

Not cause thermal or mechanical damage to the structure

Not cause sparking which may cause re or explosion

Limit step and touch voltages to control the risk o injury

to occupants

Limit damage to internal electrical and electronic systems

The lightning protection system is generally considered in

two parts. The external lightning protection system intercepts,conducts and dissipates the lightning fash to earth. The

internal lightning protection system prevents dangeroussparking within the structure (using equipotential bonding

or separation distance).

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Header Goes Here3. Introduction to Protection Methods & Risks (continued)

Non-Isolated Isolated

Figure 9. Non-isolated protection concepts.

Lightning protection systems typically ollow two approaches:

Non-isolated system where potentially damaging voltage dierentials are limited by bonding the lightning protectionsystem to the structure

Isolated system where the lightning protection system is isolated rom the structure by a specied separation distance.This distance should be sucient that energy is contained on the LPS and does not spark to the structure. Isolated systems

are well suited to structures with combustible materials such as thatched roos, or telecommunication sites that want to avoidlightning currents being conducted on masts and antenna bodies

The standard provides simple geometric orms o design whichare compromises between cost, eectiveness and simplicity in

design. The design methods are:

Mesh method

Rolling sphere method (RSM)

Protection angle method (PAM)

These methods (described in Section 9) are used to determinethe optimum location o the air-terminations and the resultingdown-conductor and earthing requirements.

A risk assessment is generally undertaken to determine the levelo risk or a specic structure, in order to make a comparison

with a pre-determined value o acceptable risk. Protectionmeasures, at an appropriate lightning protection level (LPL), are

then implemented to reduce the risk to or below the acceptablerisk. The lightning protection level determines the spacing o the

mesh, radius o rolling sphere, protective angle, etc.

It should be noted that while lightning protection is typicallyimplemented as a bonded network o air-terminals and down-conductors, other methods are permitted:

To limit touch and step potential risks:

Insulation o exposed conductive parts

Physical restriction and warning signs

To limit physical damage:

Fire proong, re extinguishing systems, protected

escape routes

3.1. Risks

To understand why typical conventional l ightning protection

systems require rigorous equipotential bonding and earthing,it is important to understand how the risk o injury due to

step/touch potentials and side fashing occur.

3.1.1. Step potential

When lightning current is injected into the earth, a large voltage

gradient builds up around the earth electrode with respect toa more distant point. The earth can be imagined as a sequence

o overlapping hemispheres. The greater the distance rom theelectrode, the larger the surace area o the hemisphere and

the more parallel paths through the soil. Thus the voltage rise isgreatest near the electrode where current density is highest.

The normal step distance o a person is near to 1 meter. At thetime o discharge being close to the earth electrode means the

voltage dierential across this distance can be large enough tobe lethal depending upon circumstances such as condition o

ootwear, etc, substantial current can fow through one lowerleg to the other.

In the case o animals, a larger risk exists. The distance betweenthe ront and rear legs o larger animals can be in the order o

2 meters, and the current path fows through the more sensitiveregion o the heart.

The hazard is considered to be reduced to tolerable level i:

The probability o persons approaching, or duration opresence within 3 m o the down-conductor is very low

limiting access to the area can be a solution

Step potential is reduced by use o 5 k ohm.m insulating

barrier such as 50 mm o asphalt or 150 mm o gravel within

3 m o the electrode

An equipotential earthing system such as mesh system iscorrectly used

It is also good practice or the upper section o the conductorentering into the earth to be insulated. Heat shrink (2 mm

polyethylene) or 4 mm thick PVC protecting the rst 2-3 mo conductor/electrode is sucient to reduce step potential

hazards. Where a conductor is insulated and buried, anyinsulated portion should not be considered as contributingto the earthing requirements o Section 12.

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Header Goes Here3. Introduction to Protection Methods & Risks (continued)

Touch potential

Steppotential

3.1.2. Touch potential

Touchpotentialisduetoasimilarreasonassteppotential,but

thevoltagedifferentialbeingconsideredisthatwhichexistsbetweenthehandand(generally)feet.Theriskofelectrocution

duetotouchpotentialisgreaterthanforsteppotential,asthepassageofcurrentowsclosetotheheartregion.

Thehazardisconsideredtobereducedtotolerablelevelif:

Theprobabilityofpersonsapproaching,ordurationofpresenceisverylowlimitingaccesstotheareacanbe

asolution

Naturaldown-conductorsareusedwhereextensivemetal

frameworkorsteelworkisinterconnected

Asurfacelayerwith 5kohm.minsulatingbarriersuchas

50mmofasphaltor150mmofgravelisused

Thedown-conductorisinsulatedwithatleast100kV

1.2/50simpulseinsulation(3mmPVC)

3.1.3. Side ashing

Alldown-conductorshavearesistanceand,moreimportantly,inductance.Duringthelightningashtherapidrateof

currentrisecancausetheinductivevoltageriseoftheconductortoreachamagnitudewheresufcientvoltage

existsfortheconductortoashovertoanearbyconductiveandearthedobject.

Sideashingcanbecontrolledby:

Usinganumberofparalleldown-conductorstoreducethe

currentineach

Ensuringtheseparationdistancebetweenthetwoobjectsis

sufcientnottobreakdowntheinterveningmedium;or

Bondingtotheobjecttoeliminatethepotentialdifference

(theobjectmaycarryapartiallightningcurrent)

Thedown-conductorandbondingrequirementsofthestandard

addresstheseissues.

Figure 10. Step and touch voltage gradients.

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4. Risk Management

4. Risk management

IEC 62305-2 provides a lightning risk management procedurethat provides a tolerable limit o risk, methods to calculate the

actual risk, and then evaluates the protection methods requiredto reduce the actual risk to be equal or lower than the tolerable

risk. The main outcome rom this risk assessment is to determinei lightning protection is required and i so, to select the

appropriate lightning class. The lightning class determines the

minimum lightning protection level (LPL) that is used within thelightning protection design.

Lightning protection can be installed even when the riskmanagement process may indicate that it is not required.

A greater level o protection than that required may alsobe selected.

It should be noted that the IEC 62305-2 document is over100 pages in length and is extremely comprehensive and

complex. A ull manual analysis o all risks can take tens o

hours to complete. Thereore or most situations a reducedanalysis is conducted, preerably with an electronic tool.For this purpose, the IEC standard comes with sotware,

and additional third-party sotware is also available.

For complex or high risk structures/situations, a more

detailed analysis should be considered using the ull standard.This would include, but is not limited to:

Locations with hazardous or explosive materials

Hospitals or other structures where ailure o internal systems

may cause a lie hazard

Note that with the national implementation o the BS EN62305-2 Risk Management standard some minor adjustmentsto the procedures and values has occurred to better refect

the localized conditions and acceptable local tolerable risk.Use the national standard appropriate to the country o

installation, or select a national standard where that countryexperiences similar lightning risk (ground fash density/

thunderdays) and similar social/economic values.

4.1. Overview o risk analysis

It is beyond the scope o this document to describe the ullrisk management requirements. Conceptually the risk analysis

ollows the general process o:

Identiying the structure to be protected and its environment1.

Evaluating each loss type and associated risk (R2.1

to R3)

Comparing R3.1

to R3

to the appropriate tolerable risk RT

todetermine i protection is needed

Evaluating protection options so R4.1

to R3 R

T

Note that separate RT

gures exist or risk o losses R1

to R3.

Lightning protection is required such that R1, R

2& R

3are all

equal or lower than the respective tolerable risk (RT).

Lightning protection may also be justied upon the economic

risk R4

and the respective economic benet. A separate

procedure in IEC 62305-2 is ollowed or this analysis.

Each o the ollowing risks are broken down into individual riskcomponents (sub categories), which are then evaluated with

regard to direct and indirect lightning eects upon the structureand on the services. This requires the computation o the

number o dangerous events, which is related to the structuresize and lightning fash density.

The simplied analysis sotware considers:

Structures dimensions

Structures attributes

Environmental infuences

Eect o services entering acility

Existing protection measures

The simplied sotware is IEC 62305-2 compliant, but is

conservative in nature. That is, worst case or conservative valuesare assumed. In situations where multiple identical structures are

to be constructed, it may be appropriate to conduct a ull riskanalysis in case a small economic saving can be obtained and

applied across the many structures.

Loss Risk to Structure Risk to Services

L1 loss o human lie R1

Risk o loss o human lie

L2 loss o essential services R2 Risk o loss o essential services R

2 Risk o loss o essential services

L3 loss o cultural heritage R3 Risk o loss o cultural heritage

L4 economic loss R4 Risk o economic loss R

4 Risk o economic loss

Risk assessment losses.Table 6.

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4. Risk Management (continued)

S1

S2

S3

S4

Lightning flashto the structure

Lightning flashto the service

Lightning flashnear the service

Lightning flashnear the structure

4.1.1. Sources o damage, type o damage,type o loss and risk o loss

For those interested in a better understanding o the riskmanagement process, or a desire to manually calculate a

structures risk, the remaining sections o this chapter provide an

introduction to the topic. It should be helpul in understandingthe eect o selection o parameters in risk assessment toolsbased on IEC 62305-1/2, and i a manual assessment is to be

undertaken, help introduce the concepts o the standards whichshould be ollowed.

It is important to understand the sources o damage, types odamage and types o losses as the procedure to assess the risk

evaluates various combinations considering structure, contents,services and environment with the source and type o damage.

IEC 62305-1 introduces the concepts o sources o damage

(Figure 11) where:

S1 Lightning fash to the structure

S2 Lightning fash near the structure

S3 Lightning fash to the services

S4 Lightning fash near to the services

With the possible sources o damage due to lightning fash

dened, three possible types o damage are identied:

D1 Injury o living beings (humans and animals) due to

touch and step potential

D2 Physical damage (re, explosion, mechanical destruction,chemical release)

D3 Failure o internal electrical/electronic systems due tolightning electromagnetic impulse

Figure 11. Sources o damage

With each type o damage, our types o losses are identied:

L1 Loss o human lie

L2 Loss o essential service to the public

L3 Loss o cultural heritage

L4 Economic loss (structure and its contents, service and

loss o activity)

Care is required with the term services, as it is dependant

upon its context within the standard. This may reer to thephysical services connected to the building (water, power,

gas, uel or data/telecommunications), or services provided tothe public (e.g. inormation services). The scope o services to

the public includes any type o supplier who, due to lightningdamage, can not provide their goods or service to the public.

For example a supermarket closed due to damage to cashregister/check-out systems, or a insurance company unable to

transact business due to phone or website ailure.

Table 7summarizes the types o damage and types o loss oreach o the our sources o damage [rom IEC 62305-1 Table 3].For each o the rst three types o losses (L1, L2 & L3), the

procedure o IEC 62305-2 evaluates the risk o these respectivelosses (R

1, R

2& R

3) and compares them to tolerable levels.

For Loss L4, the economic cost o the loss, with and withoutlightning protection, is compared to the cost o the protection

measures.

Table 8details the types o damages and losses associated witha service. As the loss and calculation o the risk o loss is dierentto that o the structure, the convention L2 & L4 are used to

dierentiate these losses.

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Source o damage(Point o strike)

Type o damage Type o loss

S1Lightning fash to the structure

D1 - InjuryL1 Loss o human lie

L4 Economic loss (1)

D2 Physical damage

L1 Loss o human lie (2)

L2 Loss o serviceL3 Loss o heritage

L4 Economic loss

D3 Failure o systemsL1 Loss o human lie (2)

L2 Loss o service

L4 Economic loss

S2Lightning fash near the structure

D3 Failure o systems

L1 Loss o human lie

L2 Loss o serviceL4 Economic loss

S3Lightning fash to the services

D1 - InjuryL1 Loss o human lieL4 Economic loss (1)

D2 Physical damage

L1 Loss o human lie

L2 Loss o serviceL3 Loss o heritageL4 Economic loss


L1 Loss o human lie (2)

L2 Loss o serviceL4 Economic loss

S4Lightning fash near to the services

D3 Failure o systemsL1 Loss o human lie (2)

L2 Loss o service

L4 Economic loss

Notes:(1) Only or properties where animals may be lost(2) Only or structures with risk o explosion and or hospitals or other structures where ailure o services or internal systems endangers human lie

Damages and losses in a structure or dierent sources.Table 7.

Source o damage(Point o strike)

Type o damage Type o loss

S1Lightning fash to the structure

D2 Physical damage

L2 Loss o service

L4 Economic loss


S3

Lightning fash to the services

D2 Physical damage


S4Lightning fash near to the services


Damages and losses in a structure or dierent sources.Table 8.

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Types o lossR

T(y-1)

IEC 62305-2 BS EN 62305-2

Loss o human lie10-5

(risk o 1 in 100,000)

10-5

(risk o 1 in 100,000)

Loss o service to the public10-3

(risk o 1 in 1,000)

10-4

(risk o 1 in 10,000)

Loss o cultural heritage10-3(risk o 1 in 1,000)

10-4(risk o 1 in 10,000)

Tolerable risk RTable 9.T.

Install further protective measures in order to reduce R1, 2, 3

NO

Structure is sufficiently protected against this type of loss

For each loss, identify and calculate the riskR

1, 2, 3

3

Identify the types of loss relevant to the structure to be protected Rn

R1 risk of loss of human lifeR

2risk of loss of services to the public

R risk of loss of cultural heritage

Identify the tolerable level of risk for each lossR

T

YES

R1, 2, 3

RT

30 mm

> 30 mm > 30 mm

> 30 mm

20d

100% I imp

10%

10%*

*Assuming 10 earth pointsand perfect current share

or

Figure 19. Use more secure connections or high current density locations.

Figure 21. Overlap requirements or rebar.

Figure 20. Rebar welding requirements or connections in concrete.

d

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Header Goes Here

Figure 23. Rebar clamps and CADWELD or connection to concrete reinorcing steel.

8. Natural Components (continued)

Figure 22. LENTON termination o rebar provides good electrical connection.

Suitable or connection to air termination Suitable or connection to ground electrode

CADWELD Exothermic connections

Mechanical connection to EN50164-1

RebarClamp

to LightningProtection System

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Header Goes Here8. Natural Components (continued)

For ease o construction and installation, a grounding plateis recommended or connection o the LPS to the concrete

member. I a grounding plate is not used, then attentionshould be given to corrosion protection at the air/concrete

interace. I the rebar is brought out then 100 mm o siliconrubber or bitumen covering should be used. Interace corrosion

protection is not required or copper, PVC covered copper orstainless steel conductors.

Figure 24. Ground plates are convenient and eliminatethe need or corrosion protection.

I welding is not permitted to the rebar, then an alternative is

to use a dedicated lightning protection down-conductor that isembedded in the concrete. This conductor should be wire tied

or clamped periodically to the rebar.

General practice is to nominate specic rebars in the main

structural columns as down-conductors, and to ensure thatthese are continuous through the entire route to ground.

The connection path should be vertical.

Full interconnection should be made to horizontal elements

such as foors and walls. For structures such as data processingcentres this is more critical, and precast aade elements should

also be bonded to provide eective electromagnetic shielding.

8.3.1. Precast concrete

Precast concrete rebar is permitted to be used as above.However precast members such as foors do not normally have

external access to rebar connections. For ull interconnection,terminations should be provided or connection to columns and

other members.

8.3.2. Prestressed concrete

Prestressed reinorced concrete is most commonly used orfooring, and rarely in vertical columns hence it is not oten

used as a natural down-conductor. I it is to be used, careis recommended due to possible unacceptable mechanical

consequences resulting rom the lightning current orinterconnection to the LPS. Only cables o 10 mm diameter

or greater should be used, and several parallel cables should

be used.

Note that prestressed concrete is oten used or acades, and in

the construction process the stressing cables are oten isolatedrom the other structural members. Should a side fash occur,

there may be cracking o the acade with damage to thecorrosion protection concrete grout used around the stressing

cable. These cables are highly susceptible to corrosion. In suchsituations, both ends o the cables should be bonded to the LPS.

CorrosionProtection

Ground

Plate

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9. Design Methods

9. Design methods

The rolling sphere method, mesh method and protectionangle method are used to determine the required positioning

o the lightning protection air-terminations. While there arelimits on the application o the protection angle and mesh

methods, generally the standard considers the three methodsas equivalent.

The rolling sphere method is recommended as the most

universal method, while the mesh method is more suitable orthe protection o fat suraces. The protection angle method

can only be used with limited vertical distances. Dierentdesign methods can be applied to dierent regions o a single

lightning protection system, provided the zones aorded byeach method overlap to protect the entire structure.

Any o these methods can be used to determine placemento the air-terminations. Permitted air-terminations are:

Rods (including masts and ree standing masts)

Meshed conductors (on building surace or elevated)

Catenary wires

Natural components

detalosIdetalosinoN

Air-terminations

Meshedconductors

Only practical forspecific circumstances

Catenarywires

S

S = Separationdistance requirement

S

S S

Meshed conductors used as air-terminations should not beconused with the mesh method. While the mesh method requires

the use o surace mounted meshed conductors (a grid) to protectfat suraces, the rolling sphere and protection angle method can

also be used to determine protection provided by elevated meshedconductors to protect a variety o compound suraces.

While the standard considers the three methods to be equivalent,recent research has questioned the true eectiveness o the mesh

method. ERICO recommends the rolling sphere method as themost eective. Rod air-terminations o height in the region o

0.5 m are preerable to shorter rods or conductors on the buildingsurace. The rolling sphere method generally provides the most

optimized design and the vertical air-terminal is ar more eectiveat capturing lightning fashes than mesh conductors installed

upon, or just above structure surace. Reer to Section 10.1or urther inormation.

The radius o the rolling sphere, the mesh size and the anglesused in the protection angle method are related to the class

o the lightning protection system. Lightning protection classI, II, III & IV relate to protection level I, II, III, & IV respectively.

For example i the risk assessment determines that a lightningprotection system with lightning protection class II is required to

reduce the risk to below the tolerable level, then the design othe lightning protection system will need to be in accordance

with the requirements o lightning protection level II (or higher).The greater the level o lightning protection (LPL I being the

greatest), the larger the resulting material requirement or thelightning protection system.

Figure 25.Air-Terminations.

The Class o LPS/LPL infuences the:

Rolling sphere radius, mesh size

and protection angle

Typical distances between down-

conductors and between ringconductors

Separation distances

Minimum length o earthelectrodes

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9. Design Methods (continued)

80

70

60

50

40

30

20

10

0

0 10 20 30 40 50 602

I II IIIIV

Class oLPS

h

Class o LPSLightning protection

level (LPL)

I I (highest)

II II

III III

IV IV (lowest)

Air-terminationProtection method

Rolling sphere Mesh method Protection angle

Rod 444 44

Meshed conductors (on structure surace)

4(1)

Meshed conductors (elevated rom structure)

44 44

Catenary wires 44 44

Note:(1)Mesh method is appropriate or the evaluation o the protection o the bound at surace. Rolling sphere and protection angle methods

can be used to determine protection o adjacent areas.

Suitability o air-termination methods and design methods.Table 17.

Class o LPS (lightningprotection level)

Rolling sphere radius (m) Mesh size (m) Protection angle

I 20 5 x 5

Refer Figure 25II 30 10 x 10

III 45 15 x 15

IV 60 20 x 20

Maximum values or design methods.Table 18.

Figure 26. Protection angle graph.

Class o LPS andTable 19.lightning protection level.

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r

H < 60 m H < 60 m

r

H > 60 m

H < 120 m

H > 60 m

H < 120 m0.8 H 0.8 H

H > 120 m

120 m

H > 120 m

120 m

Figure 27. Rolling sphere protection method.


9.1. Rolling sphere

As discussed in Section 2.3, with the rolling sphere method,an imaginary sphere is rolled over the surace o the structure.

Where the sphere touches the structure, this point is vulnerableto a lightning fash and air-termination(s) are required. The air-

termination system is placed such that the sphere only touchesthe air-terminations, and not the structure.

= 2rh h22d

Equation 2

Where d= distance between two rods (m)

r= radius o the rolling sphere (m)

h = height o the rods (m)

R

Protected zone

Protection required

Figure 28. Rolling sphere protection method.

The simplicity o the rolling sphere method is that it can be

applied in scale to a building model, or or simple buildings tosectional drawings. As detailed in Section 10, air-terminationsmay be rods, meshed conductors, catenary wires or naturalcomponents.

Note that or structures less than 60 m high the risk o fashes

to the sides o the building is low, and thereore protection isnot required or the vertical sides directly below protected areas(Figure 27). In the IEC standards, or buildings above 60 m,protection is required to the sides o the upper 20% o height,reer to Section 16.1.

9.1.1. Calculations or rolling spheremethod with rod air-terminations

When rods are to be used as the air-termination or the

protection o plane suraces, the ollowing calculation(Equation 2) is useul:

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Equation 3

where p = penetration distance (m)

r= radius o the rolling sphere (m)

d= distance between the two rods (m)


Height orod (m)

Distance between air-terminations (m)

LPL Ir = 20 m

LPL IIr = 30 m

LPL IIIr = 45 m

LPL IVr = 60 m

0.5 8.8 (6.2) 10.9 (7.7) 13.3 (9.4) 15.4 (10.9)

1 12.4 (8.8) 15.3 (10.8) 18.8 (13.3) 21.8 (15.4)

1.5 15.2 (10.7) 18.7 (13.2) 23.0 (16.2) 26.6 (18.8)

2 17.4 (12.3) 21.5 (15.2) 26.5 (18.7) 30.7 (21.7)

Note: Distances in brackets provide grid distances.

When rods are to be used as the air-termination or protection

o roo top items, the ollowing calculation (Equation 3) o

sphere penetration distance is useul:

2

2

2

=d

rrp

Examples o rolling sphere protection distance.Table 20.

Distancebetween rods

D (m)

Penetration distance (m)

LPL Ir= 20 m

LPL IIr= 30 m

LPL IIIr= 45 m

LPL IVr= 60 m

1 0.01 0.00 0.00 0.00

2 0.03 0.02 0.01 0.01

3 0.06 0.04 0.03 0.02

4 0.10 0.07 0.04 0.03

5 0.16 0.10 0.07 0.05

6 0.23 0.15 0.10 0.08

7 (5 x 5 m) 0.31 0.20 0.14 0.10

8 0.40 0.27 0.18 0.13

9 0.51 0.34 0.23 0.17

10 0.64 0.42 0.28 0.21

14 (10 x 10 m) 1.27 0.83 0.55 0.41

15 1.46 0.95 0.63 0.47

20 2.68 1.72 1.13 0.84

21 (15 x 15 m) 2.98 1.90 1.24 0.93

28 (20 x 20 m) 5.72 3.47 2.34 1.66

30 6.77 4.02 2.57 1.91

Note:Figures in brackets are the mesh size o the correspondingdiagonal distance.

Rolling sphere penetration distance.Table 21.

Figure 29. Penetration distance o rolling sphere.

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Figure 30. Example o rolling sphere method.

9.1.2. Calculations o rolling sphere methodand mesh/catenary conductors

Where the rolling sphere method is to be used to evaluate theprotection provided by mesh conductors or network o catenary

wires, the preceding two calculations (Equations 2 & 3) can

be used. The distance/height o the mesh/catenary replaces therod distance/height. In Figure 29 note that the distance orpenetration or protection distance is the diagonal o the grid

(distance between points A & B).LPL Mesh Size

I 5 m x 5 m

II 10 m x 10 m

III 15 m x 15 m

IV 20 m x 20 m

Table 22. Mesh size or mesh method.

9.2. Mesh method

For protection o a plane (fat) surace, the mesh method is

considered to protect the whole bound surace i meshedconductors are:

Positioned on the edges (perimeter) o the surace

The mesh size is in accordance with Table 22

No metallic structures protrude outside the volume(Reer to Section 10.3 consider air-terminals andRSM/PAM method to protect these)

From each point, at least two separate paths exist to

ground (i.e. no dead ends), and these paths ollowthe most direct routes

Natural components may be used or part o the mesh grid,or even the entire grid. The mesh method is recommended or

fat roo suraces. It is also recommended or the protection othe sides o tall buildings against fashes to the side (reer to

Section 16.1).

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A

Figure 31. Protection via mesh method.

Figure 32. Mesh method or compound shapes.

The mesh method should not be used on curved suraces,but can be used on non-horizontal plane suraces and

compound suraces. For example on the vertical sides o tall

buildings or protection against fashes to the side, or oncompound suraces such as industrial roos. For compoundsuraces, conductors should be placed on the roo ridge

lines i the slope exceeds 1/10.

The protective area provided by the mesh method is the area

bounded by the mesh. The protection to areas adjacent tothe mesh (e.g. building sides and lower structural points) is

determined by the protection angle method or rolling sphere

method (reer to Figure 33).

The protection provided by meshed conductors not placed

in ull accordance with the mesh method, e.g., those raisedabove the building surace, should be determined with an

alternative design method, i.e., PAM or RSM, applied to theindividual conductors. I the RSM is used, Table 21 providesa simple rule o thumb or determining what minimumdistance above the building surace the mesh conductors

would be required to be raised in order to conorm to therolling sphere method. It can be seen that this distance is

0.31, 0.83, 1.24 and 1.66 m or mesh method grids spacedto requirements o LPL I, II, III and IV respectively.

Mesh

Method

ProtectionAngle

Methodh1

r

1

Rolling

SphereMethod

Protected

Volume

Protected

Volume

Figure 33. Volume protected by meshed conductorsaccording to PAM and RSM method.

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h1

h2

Protected

Notprotected

Protected

d2

2

1

d1

Figure 36. Protection angle method applied toinclined surace.

Figure 34. Protection angle method.

Figure 35. Combination protection.

9.3. Protection angle method

Air-terminations (rods/masts and catenary wires) are located

so the volume dened by the protection angle (reer toFigure 34) covers the structure to be protected. The heighto the air-termination is measured rom the top o the air-termination to the surace to be protected. The protection

angle method is limited in application to heights that areequal to or less than the corresponding rolling sphere radius.

Where the protection angle method alone is employed, multiplerods are generally required or most structures. However the

protection angle method is most commonly used to supplementthe mesh method, providing protection to items protruding rom

the plane surace.

The protection angle method can be used on inclinedsuraces, where the height o the rod is the vertical height,

but the protection angle is reerenced rom a perpendicularline rom the surace to the tip o the rod.

h

90


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Header Goes Here9. Design Methods (continued)

Height hof air-

termination(m)

Distance d (m) and protection angle (rounded down to nearest degree)


Distance Angle Distance Angle Distance Angle Distance Angle

1 2.75 70 3.27 73 4.01 76 4.70 78

2 5.49 70 6.54 73 8.02 76 9.41 78

3 7.07 67 8.71 71 10.46 74 12.99 77

4 7.52 62 9.42 67 12.31 72 13.95 745 8.32 59 10.25 64 14.52 71 16.35 73

6 8.57 55 10.82 61 14.14 67 17.43 71

7 9.29 53 11.65 59 15.72 66 18.24 69

8 9.53 50 12.32 57 16.40 64 18.85 67

9 9.65 47 12.85 55 16.93 62 20.21 66

10 10.00 45 13.27 53 17.32 60 20.50 64

11 9.90 42 14.08 52 19.05 60 19.84 61

12 10.07 40 14.30 50 19.20 58 20.78 60

13 10.16 38 14.44 48 19.27 56 21.64 59

14 9.80 35 14.50 46 19.27 54 22.40 58

15 9.74 33 15.00 45 19.91 53 23.10 57

16 9.61 31 14.92 43 20.48 52 22.85 55

17 9.04 28 15.31 42 20.99 51 23.40 54

18 8.78 26 15.65 41 21.45 50 23.89 53

19 8.86 25 15.94 40 21.86 49 25.21 53

20 7.68 21 15.07 37 21.45 47 25.60 52

21 14.70 35 21.75 46 25.93 51

22 14.84 34 22.00 45 26.22 50

23 14.94 33 22.21 44 27.41 50

24 14.42 31 22.38 43 26.65 48

25 14.43 30 22.51 42 26.81 47

26 13.82 28 21.82 40 27.88 47

27 13.17 26 22.66 40 27.96 46

28 13.06 25 21.88 38 28.00 45

29 12.91 24 21.85 37 28.00 44

30 12.73 23 21.80 36 28.97 44

31 21.71 35 28.91 43

32 21.58 34 28.81 42

33 21.43 33 28.69 4134 21.25 32 28.53 40

35 21.03 31 28.34 39

36 20.78 30 29.15 39

37 20.51 29 28.91 38

38 20.20 28 28.64 37

39 19.87 27 29.39 37

40 19.51 26 29.06 36

41 19.12 25 29.79 36

42 18.70 24 30.51 36

43 18.25 23 30.11 35

44 18.68 23 28.57 33

45 18.18 22 29.22 33

46 28.74 32

47 28.24 31

48 27.71 3049 28.29 30

50 28.87 30

51 28.27 29

52 28.82 29

53 29.38 29

54 28.71 28

55 28.02 27

56 27.31 26

57 26.58 25

58 25.82 24

59 25.04 2360 25.47 23

Table 23. Height versus horizontal distance using protection angle method.

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Header Goes Here

ss

1

1

2

2 s

ss

Catenary Wire

Taut Wire or Rod

Figure 37. Examples oprotection angle method.


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Header Goes Here

Protection overestimated bythe protection angle method

Protection underestimated bythe protection angle method

Figure 38. Origin o protection angle.

The knowledge that the protection angle method is derived

rom the rolling sphere method helps to understand acommon question about its implementation. With reerence

to Figure 34, it may not be apparent why oc2 is less thanoc1 I a second air-terminal is installed to the let o the

existing air-terminal, then oc1 and oc2 or the second terminalwould be equal. The reason that h2 is used or oc2 is an

attempt to duplicate the protection indicated by the rollingsphere method.


9.3.1. Background o the protectionangle method

While the protection angle method appears to be similar

to the historic and simple cone o protection method, theprotection angle method is actually a derivative o the rolling

sphere method. The angles or the protection angle methodare obtained rom a rolling sphere analysis as shown in

Figure 38. This is why the protection angle method is limitedto the maximum height o the equivalent rolling sphere.

Consider a 50 m structure with rod air-termination. As a45 m rolling sphere (LPL III) would touch the side o the

structure, protection to objects at the ground level can notbe protected using protection angle with LPL III. Considering

LPL IV, a 60 m rolling sphere would not touch the side o thestructure, thus protection angle LPL IV can be used with the

rod air-termination to determine what objects at the groundlevel would be protected.

The virtue o the protection angle method is its simplicity

in application, but its drawback is that it is a urthersimplication o the rolling sphere method, hence maynot be as reliable or ecient.

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Header Goes Here

Figure 40. Typical air-terminations.

Figure 41. Rod designs to reduce risk o impalement.

Figure 39.Air-terminal interconnections.

10. Air-terminations

10. Air-terminations

Air-terminations are those items specically placed to capturethe lightning fashes. Permitted air-terminations are:

Rods (including masts and ree standing masts)

Meshed conductors (on building surace or elevated)

Catenary wires

Natural components

Air-terminations are placed in accordance with the selected

design method to provide protection to the structure.Additionally:

Air-terminations should be interconnected at eachstructure level

Air-terminations should be connected to down-conductors

as per Section 11

Mesh and air-termination interconnections should be

provided with expansion joints (reer to Section 10.5)

Rod air-terminations should be located or designed

(suitable height or tip shape) to avoid the creation oan impalement hazard

In placing conductors upon the roo, several additionalconsiderations should be taken:

Install as close as practical to roo edges

Secure per requirements provided in Table 26

Select materials to reduce risk o corrosion

Do not introduce trip hazards upon roo surace

Do not locate in areas where water may pool (e.g. gutters)

Avoid penetrations into roo or xing o conductors

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Header Goes Here10. Air-terminations (continued)

h

d

d h is recommendedto be 0.25m-0.5mminimumd is recommendedto be 0.5hmaximum

Figure 43. Recommended distances or placement.

This research does not bode well or horizontal conductorsplaced on the building via the mesh or other design methods,

as the height o the conductor is the conductor thickness,

typically 2 to 8 mm. The above research concludes that theconductor would need to be installed 1 to 4 mm rom thestructure edge. Generally, this is impossible due to the need to

install clips to asten the conductor. As these are oten screwedin place, they can not be installed close to the edge.

In accordance with the design requirements o the rollingsphere method, any horizontal conductor on a building edge

(and intended to be part o the air-termination network)would need to be virtually on the exact edge to stop the

rolling sphere rom touching the edge o the structure. TheIEC standards do not give any assistance or recommendations

on this issue. BS 6651-1991 iners that 0.1 m maximumdistance is acceptable, yet this appears to be unsubstantiated.

Due to perormance concerns, ERICO would not recommendthe use o the mesh method where horizontal conductors

(or use as air-terminations) are installed directly onto thesurace to be protected. The addition o vertical air-terminations

(rods) improves the perormance o the system considerably.For non mesh method designs, raising any horizontal air

terminations at least 0.25 m above the surace improvesperormance. I the building edge uses a coping (metallic

covering), then provided that the requirements or naturalair-terminations are met, the coping eliminates the conductor

placement concern. In many cases, at the design stage o thebuilding, the use o coping, installation o metallic hand rails or

careul selection o building materials and other structural itemscan signicantly improve perormance and reduce the visual

impact o the lightning protection system.

I the horizontal conductor is not part o the air-terminationnetwork (i.e. is part o the bonding network joining air-

terminals), then placement is not as critical provided the otherair-terminations provide protection to the desired level.

10.1. Recommendation on positioning

IEC 62305-3 provides general statements on positioning o

air-terminations, such as on corners, exposed points and edges.However, no specic dimensions or tolerances are given. Oten

the question occurs rom the installers, how close is closeenough?. The strict answer is that the positioning o air-

terminations should be compliant with the design method used(i.e. rolling sphere, protection angle or mesh method). Thereore

a good design will document exact requirements to the installeror add a saety margin to design to cover normal variances. For

example, air-terminals (rods) may be required on a parapet edgeand a good design will allow sucient height so that protection

is provided regardless o whether the rods are installed on topo the parapet, or on the inside or outside edge.

While the IEC standards allow any height o air-terminal (rod)to used, research shows that or eective protection, both the

minimum height and the relationship o the height o the air-termination to distance rom the structure edge is critical.

For air-terminals o less than 0.5 m height, these need to beless than hal their height rom the edge to be most eective.

It is recommended that a minimum height o 0.25 m beselected (0.5 m preerred), and placed as close as practical to

any edge being protected (at least within 0.5 x rod height).

Figure 42.Adhesive bases, mounting blocks and standing seamsavoid need or penetrative mounting o conductor fxings.

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10. Air-terminations (continued)

10.2. Masts and antennas

Masts and fag poles, etc, on the structure can be used as parto the air-termination system where they meet the requirements

o natural components and do not contain electrical circuits.The masts should be bonded into the LPS system.

Antennas (communication and TV aerials, etc) and mastswith electrical equipment (e.g. obstruction lighting) should beprotected by an air-termination system, preerably an isolated

system where the antenna and its mast does not conductlightning currents.

Figure 44. Protection o antenna.

For simple applications such as domestic roo top TV antennasit is permissible to simply bond the mast to the air-termination

system, but damage to antenna/mast and cabling can beexpected. Class I surge protection must be installed.

I the antenna is exposed to lightning fashes, then surgeprotection (Class I) must be installed. I the antenna is protected

by an air-termination, then surge protection (Class II) shouldbe installed. The preerred location or the SPD is as close as

possible to the entry point o the cable into the structure, andwhere possible the cable should enter into the building near to,

and be connected to an equipotential bonding bar. Screenedcables should have the screen bonded to the antenna/air-

termination and the equipotential bonding bar.

The ERITECH isolated down-conductor system provides anair-terminal and isolated down-conductor that can be mounted

directly on the mast/antenna structure to reduce the risk o direct

or partial lightning currents. The isolated down-conductor hasa special construction that allows it to be mounted directly onthe mast, but provides the equivalent separation distance o

1000 mm o air. Reer to Section 13 or urther inormation.

10.3. Protection o other items protrudingabove the roo

The design o the lightning protection system should be suchthat air-terminations are positioned to provide protection against

lightning fashes to the roo and all items located upon it (vents,skylights, air-handling units, pipes, etc). However, in some cases,

protection is not required or smaller or non-conductive items.

Table 24 summarizes the requirements or determining i air-termination protection is required.

Note that the bonding requirements or these items requires

separate consideration, reer to Section 10.4.

Table 24. Roo fxtures not requiring protection.

Roo xtures do not require protection i thesedimensions are not exceeded:

Metal RooFixtures

Height above the roo level: 0.3 m

The total area o the superstructure: 1.0 m2

The length

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