Lightning ProtectionGuidelines for InstrumentationSystemsInstallation ManualPN1:007Revision B November 1995This manual supercedes the issue dated June 1991.D3P00701202PROVOX, is a mark of one or more of the Fisher-Rosemount group of companies.All other marks are the property of their respective owners.See CE Statement in Section 1 Fisher-Rosemount Systems, Inc. 1989, 1991, 1995. All rights reserved.Printed in USAThe contents of this publication are presented for informational purposes only, and while every efforthas been made to ensure their accuracy, they are not to be construed as warranties or guarantees,express or implied, regarding the products or services described herein or their use or applicability. Wereserve the right to modify or improve the designs or specifications of such products at any time withoutnotice.Your Evaluation Please . . .Name: Title and Department:Company: Years of Experience: ___ Instrumentation ___ DistributedControlTelephone: ( ) -- Education: ____High School ____Years College ____DegreeJob Responsibility:Please indicate your evaluation of PN1:007 (Revision B November 1995). Attach extra sheets if needed.1. How and when do you use this manual? VRead entire manual before attempting taskVRead selected sections before attempting taskVRead while attempting taskVAttempt task firstVRead as last resort2. How well is the manuals contentorganized? Please explain.VExcellent parallels products operation,very usableVGood representative of the productsoperation, usableVAverage usable but can be improvedVFair not very usable, should be improvedVPoor not usable, must be improvedVNo OpinionUnderstandable Applicable3. 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Please explain.VExcellent met all needs, extremely usableVGood met most of my needs, very usableVAverage usableVFair should be revised, not very usableVPoor must be revised, totally unusableVNo OpinionPlease FAX or MAIL this form to: Fisher-Rosemount Systems, Inc.Technical Documentation EditorFAX Number: (512) 834-7200 8301 Cameron Road, MD#12Attention: Technical Documentation Editor Austin, TX 78753FISHER-ROSEMOUNT USE ONLY forwarded to:V Lead Writer V Engineering V Technical Support V Marketing V Project FileDocumentation MapPN1:007Revision B November 1995iiiPROVOXInstrumentationLightning Protection Guidelines forInstrumentation SystemsThis map shows manuals used to plan the installation of a PROVOXr ProcessManagement System. The number, title, and binder location are shown for eachdocument, identifying where specific information is located. See the descriptionson the back of this map for more information.Documentation MapInstallationManualYOU ARE HEREPN1:007Lightning Protection Guidelines forInstrumentation SystemsPN1:002Planning the InstallationPN1:003AC and DC Power and Ground WiringPN1:004Signal Wiring and Highway SystemGuidelinesPN1:005Preventing Electrostatic DischargePN1:006Environmental Considerations forInstrumentation systemsPN1:008Site EvaluationDocumentation MapPN1:007Revision B November 1995ivPROVOX documentation supports each stage of system development.System Development Stages Document Type & ContentsSystem Design Configuration Engineering ManualsConfiguration data-entry help for aproduct, including theory ofoperation for improved productuse.Installation and User Manuals forConfiguration ProductsInstallation procedures, andoperating methods and proceduresfor using the configurationsoftware.Technical Reference ManualsAdvanced user information forexpanding the capability of thePROVOX system.System Managers GuideExpert users information formanaging operating systems.System Planning andInstallationInstallation ManualsSite preparation, including theenvironment, power, andgrounding. Also, product signalwiring, cable connections, andhardware installation.System Startup andOperationUser ManualsOperating methods andprocedures for a product, andsoftware installation.TutorialsStructured training for operators.Maintenance Maintenance ManualsPreventative maintenance,calibration, troubleshooting, andrepair procedures.Ordering Information To order additional manuals, contact your localsales representative, specifying the number, title, and quantity of eachdocument required.PN1:007Revision B November 1995v1 Introduction 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.1 Intended Audience 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.2 CE Statement 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.3 Manual Conventions 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.4 Notes 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.5 Related Documents 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.6 Reference Documents 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1.7 Excellence in Documentation 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Lightning Risk Determination 3 . . . . . . . . . . . . . . . . . . . . . . . .3 Lightning Protection Systems 4 . . . . . . . . . . . . . . . . . . . . . . .3.1 Lightning Rods 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.2 Conductor System 5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.3 Grounding System 6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.4 Lightning Arrestors and Surge Protectors 7 . . . . . . . . . . . . . . . . . . .4 Implementing Lightning Protection 8 . . . . . . . . . . . . . . . . . . .5 Inspection and Maintenance of LightningProtection Systems 9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Figures1 Minimum Conductor Bend Radius Requirements 5 . . . . . . . . . . . .2 Typical Lightning Protection System 6 . . . . . . . . . . . . . . . . . . . . . . .3 Type DH7091 Transient Protection Assembly and UserSupplied Mounting Plate 10 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 Cabinet Grounding and PROVOX Highway Protection in aMulti-Cabinet Grouping 11 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5 Signal and Power Grounding, and PROVOX HighwayProtection, in a Multi-Cabinet Grouping 12 . . . . . . . . . . . . . . . . . . .6 Single Cabinet (DC Cabinet Grounding System) 12 . . . . . . . . . . . . .7 Multiple Cabinet System Grounding and TransientProtection Assembly Placement 13 . . . . . . . . . . . . . . . . . . . . . . . . . .ContentsSection/Title PageLightning Protection Guidelines for Instrumentation SystemsContentsPN1:007Revision B November 1995viThis page intentionally left blank.1 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19951 IntroductionThis installation planning manual provides guidelines for protectingPROVOXr Process Management Systems from lightning damage. Adirect strike can disrupt critical processes, start fires, damage buildingsand equipment, and injure personnel. Near strikes, too, can disruptcritical processes and damage electronic circuitry, by inducing voltage inunprotected wiring. Therefore, adequate lightning protection is essentialin a modern processing plant.1.1 Intended AudienceInstallation planning manuals are intended for use by plant engineeringpersonnel, especially those charged with planning a control systeminstallation.1.2 CE StatementIf you intend to have your PROVOX system certified for compliance toappropriate European Union directives, the following CE statement isextremely important to your ability to achieve that compliance.This manual describes installation andmaintenance procedures for productswhich have been tested to be incompliance with appropriate CEdirectives. To maintain compliance,these products must be installed andmaintained according to theprocedures described in this manual.Failure to follow the procedures maycompromise compliance.2 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19951.3 Manual ConventionsThis manual uses the following conventions:J Acronyms and Abbreviations Terms are spelled out the first timethey appear in text. Thereafter, only the acronym or abbreviation isused.J Revision Control The title page lists the revision level and theprinting date of this manual. When the manual is revised, the revisionlevel and the printing date are changed.J References References to other Fisher-Rosemount Systemsmanuals include the name and catalog number for manuals.1.4 NotesNotes attract attention to essential information in this manual. The typeof information included in a note is:NoteNotes have this form and symbol. Notes containinstallation, operation, or maintenanceprocedures, practices, conditions, statements,and so forth, that alert you to importantinformation which may make your task easier orincrease your understanding.1.5 Related DocumentsThe planning manuals listed below provide further information for systeminstallation planning:J PN1:002, Planning the InstallationJ PN1:003, AC and DC Power and Ground WiringJ PN1:004, Signal Wiring and Highway System GuidelinesJ PN1:005, Preventing Electrostatic DamageJ PN1:006 Environmental Conditions for Instrumentation SystemsJ PN1:008, Site Evaluation3 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19951.6 Reference DocumentsThe documents listed below provide further information forunderstanding lightning protection systems:J Hart, William C. and Malone, Edgar W., Lightning and LightningProtection, 1st ed., Don White Consultants, Inc., Gainesville, Virginia,1979.J NFPA, NFPA-78 Lightning Protection Code 1986, Quincy,Massachusetts: National Fire Protection Association, 1986.1.7 Excellence in DocumentationOur goal is to provide documents that meet your needs. Throughsurveys and interviews, we continually evaluate our documents as partof the broad Fisher-Rosemount Systems customer-support program.Various manuals are produced for different purposes and for readerswith varying backgrounds and experience.Please assist us in the evaluation of this manual by completing thereader evaluation form located at the front of the document. In addition, ifyou have any suggestions for specific pages, return a marked-up copyalong with your survey.2 Lightning Risk DeterminationTwo factors determine the level of protection required:J Geographic locationJ Process criticalityLightning strikes occur more often in some areas than in others.Elevation, humidity, latitude, and normal weather patterns influence thefrequency of lightning strikes in a particular geographic area. Therefore,the typical lightning storm patterns at your site will influence the extent ofprotection needed.The other factor in determining appropriate lightning protection isprocess criticality. The more critical a process, the more importantlightning protection is, even though the system may be in an area of lowlightning occurrence. If any strike or near strike, no matter how unlikely,can cause loss of control of a critical process, severe financial loss,major equipment damage, or danger to personnel, a complete lightningprotection system is appropriate.4 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19953 Lightning Protection SystemsLightning protection systems provide safe conduction paths to earthground to minimize equipment damage and personal injury. A completelightning protection system includes:J Lightning rodsJ Conductor systemJ Grounding systemJ Lightning arrestors and surge protectorsLightning rods (also referred to as air terminals) intercept lightningdischarges above a building or facility. The conductor system is a safedischarge path from the lightning rods to the grounding system. Thegrounding system lets the lightning discharge or dissipate safely.Lightning arrestors and surge protectors protect power lines, datahighway cables, instrumentation wiring, and other such equipment frominduced voltages. Together, these elements minimize lightning dischargedamage.Although a lightning protection system intercepts, conducts anddissipates the main electrical discharge, it does not prevent possiblesecondary effects, such as spark-over in nearby large metal structures.NoteTo minimize secondary effects of lightning strikes,make sure that all adjacent metal structuresinterconnect with and tie to the main conductorsystem. This construction maintains the sameelectrical potential throughout all structures in thevicinity.3.1 Lightning RodsLightning rods intercept a discharge above a structure, and direct thedischarge to a safe path. In particular, lightning rods minimize thepossibility of fire. Lightning rods should be on structures, and parts ofstructures, most likely to be struck. Therefore, chimneys, ventilators,towers, and other such higher parts of buildings should have lightningrods. The parts of flat-roofed building most likely to be struck are the roofedges. A large plant site area needs a complete system of properlylocated lightning rods.5 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19953.2 Conductor SystemOnce intercepted, a lightning discharge follows a low-impedance path tothe earth (path of least resistance). Normally, the least resistant path ismetal. A conductor system consists of one or more such metal paths.Each path must be continuous from the lightning rod to the ground.Paths must not have any sharp bends or loops. This ensures that thesystem provides the most direct path to earth for lightning discharge.As illustrated in Figure 1, no bend should form an angle of less than 90degrees, and no bend should have a radius less than 10X the diameterof the RG-6U cable used for the path (approximately 3 inches (76.2 mm).A non-ferrous metal such as copper or aluminum is the preferredmaterial for the path, as it is not susceptible to the rust or corrosion of aferrous metal.RBend angle must not be less than 90CLCLRadius must not be lessthan 10X cable diameterFigure 1 Minimum Conductor Bend Radius RequirementsThe impedance of a conductor system is inversely proportional to thenumber of separate discharge paths. Therefore, increasing the numberof paths decreases the impedance. In a multi-path conductor system, thepaths (wires) should form a cage around the structure. The steelframework of a structure can substitute for separate conductors, butsmooth connection straps must span any sharp bends or otherhindrance. Figure 2 shows a typical protection system with a conductor,grounded steel framework, and connection straps.6 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 1995Optional DownConductor If SteelFramework is not usedLightning RodsIf Down ConductorIs Used, Strap toSteel Frameworkat Top and BottomGrounding RodsSteel FrameworkConnection StrapsPlant GroundingSystemFigure 2 Typical Lightning Protection SystemIn metal structures, the conductor system can use the framing instead ofseparate conductor cables. In such cases, lightning rods should beelectrically bonded to the top part of the framework, and groundterminals should be bonded to the bottom. Structures with electricallycontinuous metal exteriors may not require separate lightning rod andconductor systems, if the metal is at least 0.188 inch (4.76 mm) thick.The metal exterior itself can intercept lightning and conduct it to theground.3.3 Grounding SystemProper grounds are essential for effective lightning protection. Installationmanual, AC and DC Power and Ground Wiring, PN1:003, includes acomplete description of recommended plant grounding systems. Eachground connection, and each branch of each ground connection, shouldextend below, and at least 2 feet (0.61 m) away from, a buildingsfoundation walls. This construction minimizes wall damage.7 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19953.4 Lightning Arrestors and Surge ProtectorsNoteLightning arrestors assist in the isolation ofcoaxial type highways, but strikes can still jumpthose systems. For the fullest protection, fiberoptic links are recommended.Lightning arrestors and surge protectors minimize current induced in thewiring of an instrumentation system. Induction can occur in two ways:J A lightning discharge passing through the conductor systemgenerates a transient magnetic field, which induces current in nearbywiring.J As the grounding system dissipates a discharge in the earth, a stepdifference in potential develops in the earth itself. This differenceinduces current in underground instrumentation wiring.Protection devices use three main types of circuits:J VaristorsJ Semiconductors (avalanche diodes)J Gas discharge tubesVaristors and semiconductors provide protection from lower currentlevels. Gas discharge tubes protect the system from high current andvoltages levels. Most protection devices have a combination of thesecircuits.8 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19954 Implementing LightningProtectionWhen planning a protection system, carefully consider environmentalconditions and plant requirements. To implement the system, followthese suggestions:J Ground the building and plant site to a single ground system. If thereis a remote or separated building at the plant site, isolate the signals,power, and communications systems of the remote building.Installation manual, AC and DC Power and Ground Wiring, PN1:003,contains additional plant grounding guidelines.J Use overhead cables when possible. The air around overhead cablesacts as an insulator, so such cables are less susceptible to lightninginduced voltage than are underground cables. Also, since overheadcables are not buried, they are less susceptible to step-potentialinduction in the earth than are underground cables. Ground bothtypes of cables, including their conduits, pipe racking and cable trays.J Install surge protectors on all cables running outside of buildings by:Installing a protection device for power wiring at either thesubstation entrance (preferred), or at each piece of poweredequipment.Installing a protection device on each phone line coming into thebuilding.Installing a protection device on instrumentation wiring, if thestructures are not all grounded to a plant-wide system. Or, theequipment is not designed to handle an induced voltage surge.J For instrumentation system communication cables, install a surgeprotector in each building at the cable entry site. Systemcommunication cables are coaxial cables for data highways andcontrol I/O busses.NoteInstall protected cables in grounded conduit orcable trays.J When building a lightning protection system, use mechanically strongmaterials with physical properties which resist rust and corrosion.9 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 1995For protecting data highways and control I/O busses, Type DH7091Transient Protection Assemblies are available. Figure 3 through Figure 7show the different methods and types of application for PROVOX cabinetgrounding combinations. Refer to installation manual, AC and DC Powerand Ground Wiring, PN1:003, for additional information on cabinetgrounding.The transient protection assemblies are grounded to the source of thesignals that are being protected. For data highways, the ground islocated within the cabinet area where the communications interfaceassemblies (CIAs and CIA IIs) are located. For control I/O busses, theassemblies are grounded in the same area as the system cabinetground. The ground can be at the cabinet level or remote I/O location,and connected to the cabinet ground system at any point from thecabinet back to the PROVOX Instrumentation Ground (PIG).5 Inspection and Maintenance ofLightning Protection SystemsBuilding additions or structural repairs done without consideration for alightning protection system can reduce the systems effectiveness.Deterioration of or mechanical damage to the system itself may reduceits effectiveness in similar ways.To prevent a loss of protection, evaluate all proposed structural changesfor effects on the protection system, and ensure that no structural repairsinhibit system protection. Inspect the structure periodically, at leastannually, for deterioration and mechanical damage. Thoroughly inspectand test the lightning protection system every five years.10 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 19951.1(27.9)1.4(35.6)1.2(30.5)Protector Top View (Mounted)INCH(mm)MountingPlate3.25(82.6)2.25(57.2)3.25(82.6)2.94(74.7)0.154(3.9)1.15(20.2)0.450(11.4)2.25(57.2)Mounting Plate Top ViewTypical 4 placesProtector Side View (Mounted)DIAHoleLINEEQUIPMounting Plate End ViewFigure 3 Type DH7091 Transient Protection Assembly and UserSupplied Mounting Plate11 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 1995DC GroundPlant Earth GroundLineNeutralGroundCabinetGroundMGBPROVOXrInstrumentationGround (PIG)GroundedSteelColumnTransient Protector.See Figure 8Notes:121233Conductor used to connect the grounding electrode to the NEUTRAL Ground bond at the source of aseparately derived instrumentation power system.(PER NEC 250.6)(CSA22.1 Section 10)Conductor used to provide a low impedance ground reference for the DC Power System (Logic,Transmitter, Output) and/or a Cabinet Ground for EMI/RFI high frequency noise protection of theinstrumentation cabinets, file and wiring sheilds.Supplemental conductor used to connect the grounding electrode for the source of a separately derivedinstrumentation Power System, directly to the Plant Ground Grid System. This conductor is used to providelow impedance ground reference for EMI/RFI high frequency noise. (Per NEC 250.81/250.83) (CSA 22.1Section 10)Cabinet 1 Cabinet 2 Cabinet 3PROVOX HighwayFigure 4 Cabinet Grounding and PROVOX Highway Protection in a Multi-CabinetGrouping12 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 1995CabinetGroundStrapsLGBSCPSCPower Bus BarTo PROVOXrInstrumentationGround (PIG)PROVOX HighwayLegendPower Bus BarTransient Protector.See Figure 8Cabinet 1 Cabinet 2 Cabinet 3Figure 5 Signal and Power Grounding, and PROVOX Highway Protection, in aMulti-Cabinet GroupingSCPSCPower Bus BarTo PROVOXrInstrumentationGround (PIG)Transient Protector.See Figure 8CabinetPROVOX HighwayFigure 6 Single Cabinet (DC Cabinet Grounding System)13 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 1995System CabinetLGBDC MGB CAB. MGBMGBTo PROVOXrInstrumentationGround (PIG)A local ground bus (LGB) is required for eachcabinet grouping of 8 or less.A cabinet ground is required for each groupingof 8 or more.GROUND WIRE SIZING CHARTPRESTOFLEX Welding Cable isrecommended.LGB LGB LGBSystem Cabinet System Cabinet System CabinetUp to 25 feetUp to 50 feetUp to 200 feet1/0 AWG2/0 AWG4/0 AWGNotes:Solid Copper BarTransientProtectionAssembliesCabinet GroundBar or CableFigure 7 Multiple Cabinet System Grounding and Transient Protection AssemblyPlacement14 Lightning Protection Guidelines for Instrumentation SystemsPN1:007 Revision B November 1995This page intentionally left blank.NotesPN1:007 Revision B November 1995NotesNotesPN1:007 Revision B November 1995NotesThis page intentionally left blank.PN1:007For more information, FAX (612) 895-2244