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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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Header Goes Here2. Theory of the Lightning Flash (continued)
LPL I LPL II LPL III LPL IV
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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Header Goes Here2. Theory of the Lightning Flash (continued)
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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4. Risk Management (continued)
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
D3 Failure o systems
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
D3 Failure o systems
S3
Lightning fash to the services
D2 Physical damage
D3 Failure o systems
S4Lightning fash near to the services
D3 Failure o systems
Damages and losses in a structure or dierent sources.Table 8.
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4. Risk Management (continued)
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. Design Methods (continued)
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)
9. Design Methods (continued)
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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9. Design Methods (continued)
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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9. Design Methods (continued)
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
9. Design Methods (continued)
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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)
LPL I LPL II LPL III LPL IV
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.
9. Design Methods (continued)
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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. Design Methods (continued)
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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