A Guide to Lightning and Surge Protection
to BS6651: 1999 Annex C
Bowthorpe Low Voltage Division Tel: +44(0) 1273 692 591 Fax: +44 (0) 1273 676 637 e-mail: lvsales@bowthorpe-emp.com
Contents
Page
What are surges, transients and spikes?
Who should read this guide?
Who are Bowthorpe?
What can Bowthorpe offer you?
Surges
What is a surge? Where do surges come from? Surges, transients, spikes - whose problem are they?
Lightning
6
Direct Coupling Earth Voltage Inductive Coupling
Risk Assessment within BS6651 What the insurers say!
7 8
Commercial considerations
BS6651: 1999 Annex C - Co-ordinated Protection The Co-ordinated Protection Strategy
9 10
Its cheaper than you think How do surge protectors work? Design considerations
Product Selection Guide
11-14
Network and Telecom Systems Product selection diagram Telecommunication and wireless protection systems
AC Power Systems
Questions and Answers Common Misconceptions
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What are surges, transients and spikes?
odays business environment is a world dominated by computers. Every aspect of our working lives depends on the efcient functioning of critical IT systems. For many companies, disruption of the IT system impacts heavily on the day to day health of the organisation. Should damage occur, the cost can be severe, in some cases, catastrophically so. Clearly, the responsibility to prevent such a disaster occurring can lie with several people within the company. In some cases, external bodies such as the companys insurer may be the driving force to implement an effective protection strategy. The objective of this guide is to familiarise you with the basics of surge protection, allowing you to effectively counter the threat posed by lightning and surges to the life of your business.
Who should read this guide?
This application guide is designed for
consultants designers speciers contractors end users users of electronic systems insurers IT managers nance directors facilities managers telecom managers technical and non-technical
people. It will enable you to select the appropriate surge suppression equipment to t any particular application and will provide an insight into the phenomena of surges, what causes them and how to stop them.
Who are Bowthorpe?
owthorpe is an internationally recognised, ISO9001 registered, specialist manufacturer of surge protectors for Mains Power, Voice and Data Systems. We have representatives on various international committees including the IEC SC37A sub committee, which is responsible for developing the worlds rst truly international surge protection standard, IEC 61643
What can Bowthorpe offer you?
Technical hotline Site surveys Consultancy advice Comprehensive product range State of the art technology Competitive prices Specication of individual
products and complete protection systems
Factory and laboratory visits,
witness tests
Professional CPD accredited
presentations
Training seminars
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Surges
What is a surge?
surge, also referred to as a spike, glitch or transient overvoltage, is a very short timescale deviation from the normal operating voltage of an electrical system. Typically lasting tens of micro-seconds, surges can reach values of several thousands of volts, thus making them particularly damaging for computer related equipment. Most surges occur on the mains supply, but they also pose a real threat to any system utilising copper communication cables, such as a Local Area Network (LAN) or telephone systems.
Most surges occur on the mains supply but they also pose a real threat to any system utilising copper communication cables
Surges 0 20ms Time 0 50s Time Voltage Voltage
8/20s surge (enlarged in time)
What is a surge? A surge is a short transient deviation of line voltage from the nominal operating level.
Where do surges come from?
ost surges are caused by an electrical load either within or outside a building being switched on or off. Particular causes of transients include large machines, lift motors, welding machines and large printers. Fortunately, most internally generated transients tend to be reasonably small (typically only a few hundreds of volts) and consequently their effects range from the short-term: data corruption, system crashes and lock-up, to the long-term: insiduous component degradation which is a major factor in system reliability assessments. Internally generated surges occur on a daily basis and can be easily suppressed utilising surge protectors in the form of plug adaptors, socket strips or in-line units. In some cases, Radio Frequency Interference (RFI) ltering is incorporated within these protectors. RFI, or noise, is rarely damaging to equipment but can be an annoyance if experienced regularly. Far more damaging to equipment and systems are the large spikes typically generated externally to the building and normally associated with lightning activity,
Far more damaging to equipment and systems are the large spikes
Where do surges come from?
Inside the Building
Factory equipment Ofce equipment Air conditioning and lift motors
Small surges can cause...
Spurious crashing of computer equipment Corruption of data transfer over networks Unexpected printer output Gradual component degradation leading to equipment breakdown
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electricity supply faults or switching of large loads within the power distribution network (National Grid/ Regional Electricity Companys [RECs]). Large transients, such as those caused when there is a nearby lightning strike, can reach values of 6000 Volts and
3,000 Amps inside a building. Surges of this magnitude can cause extensive damage to computer circuitry, literally blowing up sensitive components such as micro-chips and in some cases, causing re within computer or communication equipment.
Where do surges come from?
The Outside World
Lightning Transformer tap switching, power station, sub-station and distribution faults Power cross faults Low quality generators
Large spikes can lead to...
Failure of computer power circuits Failure of communication interfaces Irreversible damage to hardware
Bowthorpe supply a wide range of surge protection products to suit all needs
Surges, Transients, Spikes - whose problem are they?
Everyones (including yours!)
Since all types of transient disturbances can be transported via electrical wiring, nearly all electronic equipment, from telephones and fax machines to large and expensive computer systems, are at risk. The extent of damage sustained ranges from corrupted data communication to immediate physical destruction of hardware and, in some cases re risk or even
compromised human safety. You may even have already suffered equipment failure through surge damage without even knowing it! The cause of a computer breakdown often passes unknown with the computer being simply replaced or repaired. Component fatigue due to repeated transient attack goes unnoticed until its too late.
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Lightning
assessment which establishes the prominence of the building given its geographical location. The purpose of a structural protection system is to prevent damage to the fabric of the building, prevent risk of re and safeguard personnel from the dangers of inadvertent electrical shocks. From the perspective of structural protection for the building, a lightning strike to the surrounding area is of no consequence. However, from the point of view of surge protection of equipment within the building, nearby lightning strikes are as important as direct strikes. The reason for this is that a structural protection system is dealing with the primary effects of the lightning strike, whereas surge protection is dealing with the secondary effects of lightning. The following diagrams portray three important mechanisms by which lightning strikes can affect sensitive equipment.
Direct Coupling
y far the most prominent cause of damaging transients is nearby or even direct lightning strikes. Lightning discharge currents can be as high as 200,000 Amps in the UK, with the average discharge current being 28,000 Amps. Obviously, such massive currents would vaporise any electronic equipment or cabling in the case of a direct strike to a cable. Fortunately, this situation is rare as most equipment and cabling is located within a building. Lightning will always tend to strike the most prominent feature, which is invariably the roof of the building! The British Standard for Lightning Protection : BS6651:1999 goes into great detail on the whys and wherefores of designing and installing a structural protection system (lightning conductors) for the building. The decision as to whether to install a structural protection system is essentially based on a risk The bulk of the discharge current from a direct strike to a power conductor pylon, for example, will be conducted to earth. Some proportion of the discharge current, however, will be conducted as a surge on the cable. The magnitude of the surge current varies due to the length and type of the cable as well as the magnitude of the lightning strike. Sensitive equipment can therefore be damaged even when the lightning strike is some distance away.
Direct Coupling
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Earth Voltage
During a cloud to ground lightning strike, the strike point is raised to a very high voltage owing to the large current (up to 200kA) being conducted through the ground (which has a nite resistance). Typically this value could be in the hundreds of thousands of volts for a fraction of a second. The further away from the strike point, the lower the voltage value. Depending on local soil conditions and climate, this voltage disturbance can be signicant up to about 2km away. As a consequence of this earth voltage disturbance, any building within 2km of a lightning strike will experience a uctuation of its mains earth voltage. Because the equipment within the building may be connected to other electrical systems, such as equipment in another building, the electricity substation etc., there exists a situation where
the power and data cables entering the building may experience different earth voltages at each end. This causes a current to ow in the connected electrical wiring which is perceived by the equipment as an incoming surge.
Earth Voltage
This basic electrical phenomenon is responsible for the third mechanism of lightning associated surges. A cloud to cloud lightning strike, of which there are approximately up to 1 million a year in the UK, sets up a massive electromagnetic eld. Any cable which lies within this eld is subject to the electromagnetic forces of it. Induced currents are created, especially prevalent where there is a large network of cables above ground. Lightning strikes to nearby pylons, trees etc produce similar results.
Inductive Coupling
Inductive Coupling
A current carrying cable, by virtue of its electromagnetic eld, will induce a current ow in any nearby cable running parallel to it.
Risk Assessment within BS6651
ifferent areas of the country and the world experience higher levels of lightning activity than others, and the climate largely determines the overall trend. Many of the variable factors are built into the risk assessment procedures in BS6651. The risk assessment for structural
90 80 70 60 50 40 30 20 10 0 10 20 30 40 50 60 70
protection is essentially determining how prominent the structure is and therefore how attractive it is to a lightning strike. The risk assessment for surge protection is more complex. As well as determining how vulnerable the building is to a direct strike, the risk assessment takes into account the quantity of external cables
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National Grid Northing (km)
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National Grid Easting (km)
60 40 80 40 100 80 20
20 10 20 100 140 80 60 60 5 40 120
0.1 0.2 0.3
0.4 0.5 0.6
The lightning density map was compiled by Electricity Association Technology Limited from data accumulated over four years from its Lightning Location System.
Number of lightning ashes to the ground per km2 per year for the uk
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entering the building and the nature of the equipment within the building as this determines the Consequential Loss factor should a system be affected. Although the risk assessment procedure can be a little complicated, with care it can be a powerful tool to establish a realistic appraisal of the risk to a system.
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NOTE: This map is based on information from the World Meteorological Organisation records for 1955.
Map showing thunderstorm days per year throughout the world
Extracts from BS6651 are reproduced with the permission of BSI. Complete editions of the standards can be obtained by post from BSI Customer Services, 389 Chiswick High Road, London W4 4AL.
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What the Insurers Say!
owadays, with the ever increasing amount of information technology being used for businesses, the costs of equipment repair and replacement have become a major concern for the insurance companies. In some cases, they have provided the nances to replace computer systems worth some 100,000s that have been destroyed by lightning or other surge phenomena. Downtime and other consequential losses often cost far more to replace. Many other cases occur in domestic and small business applications where equipment worth 100s or 1,000s has been damaged. The insurance companies now recognise surge protection as being a solution to this problem. They know that a total protection system can be tted for a fraction of the equipment replacement value.
Commercial Considerations
An organisation that has taken BS6651 very much to heart is the Loss Prevention Council, or LPC. The LPC is funded by the Association of British Insurers and Lloyds of London and is involved in all aspects of loss prevention and risk control on a world-wide basis. It is, therefore, the body that the insurers refer to for guidelines when drawing up their insurance policies and assessing potential relatively new risks. BS6651: 1999 Annex C has been taken very seriously by the LPC and, in turn, the insurance companies, particularly in light of recent avoidable claims for computer hardware damage and consequential loss as a result of surges, spikes and transients. LPC statistics on claims for hardware and consequential loss have astonished insurers to such a degree that they have had to reassess premiums for any company heavily reliant on information technology. A single such claim for over 0.5 million to one insurer has certainly focused the insurance industrys attention to this subject. It is now becoming the insurers policy to either demand higher premiums or even refuse cover if the recommendations of BS6651 are not acted upon! The statistics reveal that 60-70% of commercial claims could be directly attributed to computer hardware failure and consequential loss due to surge disruption or damage. Clearly, no organisation appreciates higher insurance premiums, but, equally, no successful company can accept computer failure resulting in poor customer service.
Latest statistics on claims for hardware and consequential loss have astonished insurers to such a degree that they have had to reassess premiums for any company heavily reliant on information technology.
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BS6651: 1999 Annex C. - Co-ordinated Protection
he British Standard BS6651: 1999 is titled Code of Practice for Protection of Structures Against Lightning and outlines the general principles of applying lightning protection to buildings and structures. It was in 1992 that Appendix C (changed to Annex C in the 1999 revision) was originally incorporated within BS6651 and provided general advice on protection of electronic equipment within or on structures against lightning. BS6651: 1999 Annex C gives details on the following aspects of surge protection: Each BS6651 location category is divided into three groups which suit different exposure or lightning risk levels. These are known as the low, medium and high system exposure levels. Bowthorpe products are suitable for the high system exposure level of each category and also address the lower exposure levels. By designing our products in this way, we greatly simplify product selection. The surge ratings for each location category are the peak surge voltage and peak surge current that will normally occur at that location in the supply network. Any protection device designed for these categories must be able to withstand the respective peak surge current and voltage. The following table indicates the protection levels required for the high system exposure group of each category.
Location category Peak surge voltage Peak surge current C 20kV 10kA B 6kV 3kA A 6kV 500 A
How to assess the lightning exposure risk to equipment Routes along which surges can enter a building and where they go within the building Deciding factors for installing protection Recommended levels of protection in a co-ordinated protection system
AC Power Protection
For AC power, Annex C denes three different categories of surge protection that vary in surge handling ability, each designed for installation at particular locations within a building supply network.
Network & Telecom System Protection
Annex C also denes a location category C for communication systems which species a 10kA protection level. However, communication cable exhibits a higher electrical impedance that helps to dissipate the surge energy. In communication systems, therefore, as long as category C protection is tted, it is not normally necessary to protect against incoming surges at location categories B and A.
Category C - The supply side of the incoming distribution board Category B - The mains distribution system Category A - The load side of socket outlets
Although not conrmed in BS6651, these three categories reect with the location categories used in the American standard IEEE C62.41 (1991).
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The Co-ordinated Protection Strategy
Its cheaper than you think
By carefully selecting which parts of the computer system are most critical to your business operations, implementing total protection need not be very costly and will easily be within the reach of small and large businesses alike. A risk assessment should be performed to identify key equipment and to weigh the costs of protecting this equipment against the potential losses to the business in system downtime, maintenance and reduced performance.
How do Surge Protectors work?
Different kinds of protector use different types of components or combinations thereof to suppress surges, transients and spikes. As described earlier in this guide, a surge is a rapid uctuation in voltage occurring on a signal or AC power cable which, in many cases, will contain enough energy to cause disruption to communications and often physical damage to electronic circuitry. The suppressor components used are normally one of three basic technologies:
gas discharge tube metal oxide varistor solid-state semi-conductor.
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Design Considerations
To be effective, surge protection must survive the maximum transient overvoltages and resultant currents that occur at the different locations and only pass the residual part of the surge that will not cause damage. It is therefore necessary to know the equipment transient design level (ETDL) for the equipment to be protected. This is the maximum surge voltage level that will not impair the performance of the equipment and is also known as the immunity level. The residual part of a surge which passes through the protector is known as the let-through voltage or transient control level (TCL). For protection to be effective, the TCL must be less than the ETDL and include a reasonable safety margin Vm:
To be effective, surge protection must survive the maximum transient overvoltages and resultant currents that occur at the different locations and only pass the residual part of the surge that will not cause damage.
All work by reacting to the excess voltage caused by the surge and by changing electrical state to conduct the surge energy safely to earth. If correctly specied, they will reduce the surge voltage to below the withstand voltage of the connected equipment. In normal conditions, when the surge has passed, the components return to their standby state. The type of technology used depends on the application. Gas discharge tubes or metal oxide varistors are ideal where a high surge rating is required, for example, category C. They do, however, suffer from being slow to respond so are often used in conjunction with other components forming a hybrid circuit. Semi-conductor suppression is suited to the very sensitive devices used on computers and communication lines.
TCL+Vm <ETDL
Equipment manufacturers can normally supply the ETDL of their equipment, however, our protectors are designed to protect even the most sensitive equipment, so the end user has no need to nd out what the ETDL is. The work is already done. As an example, the typical ETDL for a computers mains input is around 1250V. A protector capable of suppressing to a TCL of 800V will leave a safety margin of 450V.
Product Selection Guide
Bowthorpe products are each designed for specic applications and BS6651 location categories. The following steps outline the product selection process.
Category C Products Modular Distribution Surge Protector - MDSP 150 & 300 Series
Distribution panel protectors for three-phase power systems featuring exceptionally high surge handling capacites of 150kA and 300kA. They are intended for high lightning exposure areas and critical systems where long life and low maintenance are required and far exceed the recommendations of BS6651. Normally open and normally closed relay contacts provide remote
AC Power Systems Step 1: Location Category C
Identify where cables enter the building or facility. These points are where large lightning and switching surges may appear and must be dealt with rst.
MDSP 150 and 300 Series
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indication of protection status. Models with Silicon Avalanche Diode Modules (SAD) with extremely low clamping and exceptionally fast response times are particularly suited to mobile telecom applications.
Category A Products Protector Plugs and Adaptors
This range of single-outlet surge suppressors and hardwired plugs are available with surge only protection and various ratings of RFI ltering. UK, French and German formats are offered and all units feature thermal protection against surges exceeding their rating, unlike most low cost products.
DSP1 and DSP3
MDSP DIN rail mount replaceable modules
General purpose, hard-wired, single and three-phase distribution panel protectors with 30kA of surge capacity. Optional relay contacts provide remote indication of protection status.
Socket Strips
These AC mains socket strips are available in UK, French and German formats with options for surge protection, RFI ltering and a choice of from four to ten socket outlets. All strips feature thermal protection.
Step 2: Location Category B
DSP1 and DSP3
Identify sub-distribution panels that supply mission-critical hardware such as mini-computers, PABX systems, network le-servers and mainframes. Install the location category B protection described below. With the increasing use of distributed networks, many users prefer to protect all sub-distribution panels with these economically priced products.
Network and Telecom Systems Step 1: Location Category C
Locate all communication cables entering the building including PSTN dial-up voice lines and leased lines, ISDN and network lines. All incoming cables that carry signals on wire conductors must be tted with appropriate category C protection from Bowthorpes extensive range of datacom, telecom and network barriers.
6651C Protector
Category B Products 6651C Protector
A compact, hard-wired, panel mounting protector for sub-distribution panels available in single and three phase models.
Spur Protector
Spur Protector
Ideal for the protection of equipment on individual ring mains, this unit can be either wired to equipment as an inline protector or can be hardwired into wall mounted conduits.
Category C Products Network Barrier & Telecom TLP Series
10kA rated barriers are available in DIN rail mounted format for datalines. For telephone PABX systems, Krone mounted units are available in 10-line and single-line variants.
Step 3: Location Category A
Plug-in mains protection products
Fileservers, mainframe computers, PABX, and other such hardware are important for providing critical services to the company and should, therefore, be tted with category A protection. Our range of plug-in devices and socket strips provide ne-tuned, backup protection for the most important equipment and will suppress surges and interference from inside the building.
Network Barrier & Telecom TLP Series
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Supply Distribution Surge Protector Sub-distribution Panel Protector
3
DIN-rail mountable dataline surge protection
Bowthorpe Low Voltage Division Tel: +44(0) 1273 692 591 Fax: +44 (0) 1273 676 637 e-mail: lvsales@bowthorpe-emp.com
SURGES ARE GENERATED OUTSIDE BUILDINGS BY LIGHTNING, POWER FAULTS, SWITCHING AND CONTACT BETWEEN POWER AND COMMUNICATIONS LINES, ETC.
WALL CONDUIT FOR MAINS AND DATALINE CABLING
SURGES ARE GENERATED INSIDE BUILDINGS BY AIR CONDITIONERS, LIFTS, PHOTOCOPIERS, DRINKS MACHINES, FACTORY MACHINERY, REFRIGERATORS ETC.
EXTERNAL DATA CABLING FACTORY UNIT
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SECURITY OFFICE
Spur and Inline Surge Protector
TRANSFORMER BACKUP GENERATOR
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POWER, SECURITY AND COMMUNICATIONS LINES
Surge Protected Adaptors with Fax/Modem Protection
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P.A.B.X. AND OTHER COMMUNICATIONS EQUIPMENT
11KV POWER (3-PHASE)
415V POWER (3-PHASE)
UNDERGROUND CONDUITS
P.S.T.N. AND I.S.D.N. COMMUNICATIONS LINES
COLOUR KEY: POWER LINES SIGNAL LINES
Service Entry Surge Protector
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Telecom surge protection
Surge Protected Socket Strips
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Surge Protected Socket Strips c/w Telecom Option
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Telecommunications and Wireless Protection Systems
Aircraft warning light
Typical steel cabin/equipment room Microwave dish TV antenna
FM broadcast or mobile telephone antenna
Transmission equipment
Digital switching equipment
DC power equipment (batteries, rectiers, inverters, converters)
Tower footing ring earth
Equipotential earth bonding
Mains power supply
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Common earth bar connected to all electronic equipment and bonded to the earth ring
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Induced surge into buried telecom cable
MDSP AC power protection
Surge protector installed on AC power supply to aircraft warning light
Telecommunications line protector installed in MDF to protect sensitive telecoms equipment
Co-axial surge protector barriers
Modular Distribution Surge Protector
FEATURES: Exceptionally high surge handling Two stage (redundant) protection Replaceable DIN rail mount modules Dual thermal/current overload fusing Status indicators with remote signalling Silicon Avalanche Diode models available for extremely low clamping and exceptionally fast response time Site wiring fault indicator APPLICATIONS: Front end of building protection for mission critical sites and applications SAD models particularly suited to mobile telecom applications.
Distribution Surge Protectors
FEATURES: High surge handling capability Two stage (redundant) protection Full protection status indicators Remote signalling version available Fast response time and low letthrough voltage APPLICATIONS: Front end of building protection Sub distribution panel protection Individual protection of critical & costly equipment such as computer systems
Telecom Line Protectors
FEATURES: Surges reduced to below normal signal voltage High surge handling capability Negligible effect on normal line operation Models available for connection to LSA-Plus termination strips Optimum performance with lightning related surges APPLICATIONS: PABX PSTN Telephone and facsimile Computer communications using voice line modems
Network & Signal Line Barrier Protectors
FEATURES: Din rail or panel mounting Low let-through voltages Fast response times High surge handling capability Negligible effect on normal line operation APPLICATIONS: LANs EPOS CCTV Ethernet Plant & Process Control Signalling and telemetry
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Questions and Answers
I didnt hear anything about surges and transients ten years ago. Why are they causing problems NOW?
Q
A
failure. These spikes are frequently caused by utility power switching and heavy industrial power users.
Todays computers use smaller and more sophisticated electronic components than ever before which are far more sensitive to transient voltages than earlier technologies. Furthermore, we can now put computers and communication equipment anywhere we want so must be aware of variations in the quality of different operating environments. Perhaps more importantly, the electricity supply companies are not required to provide computer-grade power, so it is our responsibility to ensure the power used for our computers is clean.
Is it possible for transients to affect my equipment unnoticed?
Absolutely. Small transients can be an invisible problem, they dont necessarily cause immediate equipment failure, but WILL cause micro bullet holes inside semi-conductor electronics leading to degradation. After some period of time, the hardware will fail and be replaced under the assumption that it died a natural death of age. However, its life expectancy is actually shortened by the degrading process. In other words, the useful life of computer equipment can be extended by installing surge protection.
Q A
example, different types of computer network use a variety of connector formats, signal levels and operating frequencies. Some applications are contained within one building, however, others include data and power connections between several buildings which have different protection needs.
Surge protectors continuously monitor the power or signal line for overvoltages. When the voltage rises above a certain level components inside the protector divert the excess energy to earth and limit the voltage to a safe level.
Q A Q A
How do surge protectors work?
What is thermal overload protection and why do I need it?
Bowthorpe products have thermal overload protection tted as standard. Surge protection products where protection elements are not tted with this safety feature can overheat under fault conditions and give rise to the risk of electric shock or re.
We get very little lightning in my area. Do we still need transient suppression equipment?
Lightning is only one source of transients. Repetitive, low level spikes on power and communication lines cause circuit degradation and eventual
Q A
Is there one complete solution that provides total protection?
Q A
Every system and application is different in one way or another. For
Common Misconceptions
I dont need surge protection because my building already has structural protection. WRONG! My site is surrounded by tall buildings, so is safe from lightning damage. WRONG!
Structural lightning protection and lightning
conductors do not protect the sensitive equipment within the building.
Tall buildings may attract lightning away from
your site, but, your systems will be at risk from the secondary effects caused by the electromagnetic pulse generated when lightning strikes nearby. Your site is also at risk from surges and transients present on incoming power and communication cabling.
I dont need surge protection because my system is connected to a UPS. WRONG!
Most UPSs are not designed with BS6651 in mind
and consequently any surge protection tted is likely to be limited in its surge handling capability. Any protection tted inside the UPS is specically designed to protect its own electronics, not the equipment connected to it. UPS bypass switches, when in operation, reduce any protection afforded by the UPS.
The cabling between my two buildings is underground, so doesnt need protection. WRONG!
When lightning strikes the ground, even 1 or 2
km away, the current discharged raises the ground potential in the surrounding area by 100,000s of volts depending on proximity to the strike. While the current dissipates through the ground, a difference between the building earth points stresses the cable and any connected equipment.
Lightning never strikes twice. WRONG!
A site that has been struck once is clearly
susceptible and will often suffer problems on a regular basis.
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