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Effective surge protection concepts re-quire not only equipotential bonding butalso the use of surge protective devices(SPDs) in the field of power supply sys-tems and information technology. SPDslimit interference resulting from close,distant and direct lightning strokes tosystem-compatible values thus increasingsystem availability. Standard IEC 61643-21:2000-09 [1] specifies performance re-quirements for SPDs and testing methodsfor using SPDs in telecommunicationsystems and signalling networks. Addi-tional recommendations concerning useand application of SPDs are specified inIEC 61643-22 or pre-standard CLC/TS

61643-22:2005-09 [2] and also in thenew standard series IEC 62305-1 to -4

[3-6]. These standards contain infor-mation on energy coordination of surgeprotective devices as well as specifica-tions concerning possible conducted inter-ferences, which have to be discharged bya surge protective device. The most ener-getic interference is caused by direct light-ning strokes into a cable or into surround-ing buildings.

Interference due to lightningstrike into a cable

When telecommunication cables aredirectly struck by lightning, it can be as-sumed that the cable insulation is dam-aged and the lightning current is splitequally in both directions. IEC 62305-1[3] gives examples of impulse currents,which may flow. Table 1 shows the inter-ference depending on the lightning pro-tection level (LPL). The lightning protec-tion level defines the total lightning cur-rent and varies between 100 kA (LPL IV)and 200 kA (LPL I).

Interference due to lightningstrike into a building

When estimating the lightning protec-tion level for an IT-based system, the di-rect lightning strike into a building andthe resulting interferences have to be tak-en into consideration. Within the scope ofa protective concept, actions are taken toprevent interference, which consider bothgalvanic coupling of conducted interfer-ence currents with the lightning current

curve (10/350 µs) and radiated electro-magnetic interference with the resultingimpulse current curve of the wave form(8/20 µs). The wave forms (10/350 µs) and(8/20 µs) have in fact similar pulse risecharacteristics of 10 µs and 8 µs, howe-ver, they differ in decay time to half val-ue almost by a factor of 18. Consideringall aspects, the energy content of the10/350 µs pulse is higher by a factor of

25 than the 8/20 µs pulse provided thatamplitudes are comparable. It is neces-sary to use appropriate SPDs (Fig. 1) inorder to discharge these energies withoutcausing damage. An adapted protectivedevice design has proven its worth in sev-eral protective stages corresponding tothe lightning protection zones (LPZ) con-

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Components & Periphery

Lightning and Surge Protection for Telecommunications and Signalling Networks

Nowadays it is inevitable to take actions to protect IT-basedsystems against lightning currents and overvoltages as businessoperations of almost every company depend on the reliabilityand availability of these systems. If servers, production controlsor the complete electronic data processing centre fail over aperiod of several hours, this results in severe limitations onproductivity and consequently in higher financial loss. EMC(Electromagnetic Compatibility) constitutes an important role.Lightning currents, overvoltages and electromagnetic fields aresources of interference, which have to be controlled.

Peter Zahlmann • Herbert Krämer

Dr.-Ing. Peter Zahlmann (52),

VDE, Managing Director of DEHN + SÖHNE GmbH

+ Co. KG based in Neumarkt(Oberpfalz), Germany

E-mail: peter.zahlmann@technik.dehn.de

Dipl.-Ing. (FH) Herbert Krämer (40),

Product Manager at DEHN + SÖHNE GmbH

+ Co. KG based in Neumarkt (Oberpfalz),

GermanyE-mail: herbert.kraemer@

dehn.de

Table 1: Exemplary impulse currents fortelecommunication cables according to IEC62305-1 [3]

Fig. 1: BLITZDUCTOR XT

LPL I to II III to IV

Impulsecurrent

2 kA (10/350 µs)

1 kA (10/350 µs)

cept according to IEC 62305-4 [6]. Ac-cording to this concept, the lightningelectromagnetic pulse subdivides the bu-ilding to be protected into internal light-ning protection zones of different threatvalues. Thus, areas can be differentiatedand individually adjusted to the threatvalues and the immunity of the electro-nic system. Table 2 is intended to facili-tate the selection of the appropriate SPDfor the interference to be expected. SPDsdischarging the impulse current withoutdestruction have to be used at the rele-vant LPZ interface.

The combined lightning current andsurge arrester BLITZDUCTOR XT for foursingle wires is tested according to IEC61643-21:2000-09 [1] and has a total dis-charge capacity of 10 kA (10/350 µs) and

20 kA (8/20 µs). Furthermore, this com-bined lightning current and surge arrestermeets all requirements on the dischargecapacity (please refer to Table 1 and 2).

Fig. 2 shows an example of the cascad-ed use of SPDs at the LPZ boundaries. Thefirst SPD (D1) at the entry of the buildingprotects the installation from destruction.The consecutive SPDs (C2 and C1) reducethe interference energy to an extent,which is compatible to the consecutivesystem or the device to be protected.

Energy coordinationCLC/TS 61643-22:2005-09 [3] speci-

fies basic requirements for energy coor-dination of SPDs in the field of infor-mation technology. Energy coordina-tion between two SPDs or between SPDand IT equipment (ITE) ensures that theinitial voltage protection level of theupstream SPD resulting from an over-voltage load does not exceed the initi-al surge immunity of the downstreamdevice. Thus, energy coordination is

characteristic for such installations interms of quality.

In Fig. 3 energy coordination bet-ween the elements is met, if Up < UIN

and Ip < IIN.

Immunity of IT equipment to beprotected

During testing for electromagneticcompatibility (EMC), electric and elec-tronic equipment (devices) has to showa predefined immunity against con-ducted pulse-shaped interference (sur-ges). Requirements on and proof ofimmunity are specified in IEC 61000-4-5 [8].

Since the devices are used in diffe-rent electromagnetic ambient condi-tions, they place different demandson immunity. The immunity of a de-vice depends on the test level. Toclassify the different immunities of ITequipment, the test levels are sub-divided into four different stages (Ta-ble 3). Test level 1 includes the mini-mum requirement on immunity of thetest object. For detailed informationon the test level please refer to the

documentation of the device or evencontact the manufacturer of the de-vices.

Choosing the appropriate SPDIf SPDs are used in an energy-coordi-

nated way, SPDs of the Yellow/Line pro-duct line discharge conducted interfer-ences without destruction and limit to safe values so that immunity of the ITequipment is not exceeded. For this pur-pose, the SPD has to be chosen in such away that its let-through energy is belowthe EMC test values according to IEC61000-4-5 [8] of the IT equipment. In ad-dition, the specified discharge capacityhas to correspond at least to the interfe-rence to be expected. Since energy co-ordination can only be determined by means of high measurement effort, it makes sense that surge protective devicesare marked by the manufacturer. Energycoordination is marked in an easy under-standable way by means of the symbol ofthe SPD class of the Yellow/Line surge

4 Heft 2/2007 •

Table 2: Exemplary impulse currents per cable wire according to CLC/TS 61643-22:2005-09 [2]

Table 3: Test levels for electronic equipmentaccording to IEC 61000-4-5 [8]

Fig. 3: Coordination of two SPDs according to CLC/TS 61643-22:2005-09 [2] with UIN2, UINEG

= open-circuit voltage of the generator used for resistibility verification; IIN2, IINEG = short-circuitcurrent of the generator used for resistibility verification; Up = voltage protection level; Ip = letthrough current

SPD 1 SPD 2 ITG

IIN1

UIN

1

Up1

UIN

2

IIN2Ip1

Up1

UIN

EG

IINEGIp1

Lightning protection zone (LPZ) LPZ 0/1 LPZ 1/2 LPZ 2/3

Impulse current / cablewire

0,5 kA…2,5 kA (10/350 µs)

0,25 kA…5 kA (8/20 µs)

0,25 kA…0,5 kA (8/20 µs)

Level Open-circuit test voltage±10%

kV

1 0,5 kV

2 1 kV

3 2 kV

4 4 kV

Fig. 2: Using SPDs at LPZ boundaries (CLC/TS 61643-22:2005-09 [2])

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protective devices. This symbol can befound in the data sheet and on the typelabel of each SPD of the Yellow/Line product line. 7) The symbol of the SPDclass graphically combines three impor-tant features of the SPD and may consistof an individual symbol or of a combi-nation of individual symbols. These sym-bols help to determine the discharge ca-pacity according to IEC 61643-21:2000-09 [1], the protective effect according toIEC 61000-4-5 [8] and the energy coor-dination according to CLC/TS 61643-22:2005-09 [2].

For example, an SPD with “puzzlenose” is energy-coordinated to an SPDwith “puzzle hole“. If there is a square in-cluding the letter P and a number on theright-hand side of the symbol, the SPD isenergy-coordinated to a downstream ITequipment at the corresponding test level(Fig. 4 and 5). In addition, SPDs are sub-divided according to discharge capacityinto TYPE 1 to TYPE 4, whereas TYPE 1SPDs can carry lightning currents. TYPE2 to TYPE 4 are surge arresters, the dis-charge capability of which is designed forlower energy transients. TYPE 2 SPDs candischarge overvoltages and current peaksup to 2.5 kA (8/20 µs), which may resultfrom field impact of lightning strokes.Since the discharge capacity decreaseswith increasing ordinal number, it ap-pears to be reasonable to use TYPE 3 andTYPE 4 SPDs as EMC IT equipment pro-tection for the user.

Test specifications for SPDsA protective device can be overloaded

during operation by discharges, whichexceed device specifications. Therefore,for ensuring high system availability it isimportant to test SPDs on a regular basis.IEC 62305-3 [5] generally describes main-tenance tests and test intervals of an LPS.During maintenance SPDs have to be tested for the purpose of equipotentialbonding. The frequency of maintenanceto be carried out depends on the follow-ing factors:

• Quality loss due toweather and ambientconditions

• Impact of direct light-ning strokes and pos-sible damage

• Class of LPS of the bu-ilding on siteTable 4 should be regarded as general

recommendation for lightning protectionsystems.

However, these specifications may dif-fer depending on the requirements ofoperators or specific directives.

Simplifying testing by means ofSPDs with integrated LifeCheck

As a rule, SPDs for power supply sys-tems have visual or acoustic fault indica-tion enabling faster fault detection. In themajority of cases, SPDs for IT-based sys-tems do not have an integrated displayfor faults or overloads and therefore ha-ve to be tested by means of special SPDtest devices. Frequently pluggable SPDsare used in order to avoid that the pro-tective device has to be removed for tes-ting. They consist of a fixed base part anda pluggable protective module. The test isrelatively complex as the protective mo-dule has to be removed, tested and beplugged in again. In addition, the signalcircuit is not protected during testing.

However, pluggable SPDs such as theBLITZDUCTOR XT, which have integratedLifeCheck in their protective modules, areparticularly easy to maintain. LifeCheckuses modern RFID technology (Radio Fre-quency Identification) for controlling the

protective circuit and for communication.SPDs with integrated LifeCheck enablefast and easy testing of surge protectionduring operation. Thus, SPDs can be test-ed without causing downtimes of the sys-tem. The LifeCheck control circuit is ableto detect extreme thermal or electric loadson the protective elements. This can beread out within seconds and contact-freeby means of a reader using RFID techno-logy (Fig. 6). Whenever the reader dis-plays “OK“, no overload was detected. Inthe contrary case, the module has to beexchanged as soon as possible in ordernot to endanger the availability of thecircuit protected. Since the LifeCheckcontrol circuit might activate the faultsignal already below the destruction limitof the SPD, signal interruptions can beavoided by means of exchanging themodule in time.

Space-saving SPDs are more cost-effective

SPDs have to be integratable into a sys-tem to be protected at low effort in orderto make the use of SPDs more cost-effec-tive. It is necessary to mechanically adaptthe SPD design to the installation envi-ronment. Frequently the earth cable isconnected to the in-house cable in a dis-

5• Heft 2/2007

Components & Periphery

Table 4: Inspection intervals according to IEC 62305-3 [5]

Fig. 4: Structure of the Yellow/Line SPD class symbol

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(year)

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(year)

I and II 1 2 1

III and IV 2 4 1

tribution board via supporting bar tech-nology. Equipotential bonding is carriedout in this distribution board making ittherefore particularly suitable for the in-stallation of SPDs. In practice SPDs areinstalled instead of the already existing ter-minal blocks when retrofitting the light-ning equipotential bonding. If originally6 mm double-stack terminals are used fortwo signal lines, the SPD has to have amaximum width of 3 mm per line to beprotected. If these dimensions cannot bemet, the wiring and the distribution bo-ard have to be exchanged, which resultsin considerably higher effort. Thereforethe combined lightning current and surgearrester BLITZDUCTOR XT consisting ofbase part and SPD module proves to beparticularly cost-effective. The combinedlightning current and surge arrester offerseffective protection for four active signallines over a total width of only 12 mm(Fig. 7). The universal base part, whichcan be used for any SPD module, opti-mises storage and promotes prewiringand service. If a module has to be ex-changed, the new design of the deviceenables both safe plugging and easily re-moving the SPD module without signalinterruption in the base part. The SPD issecured as soon as the modules snaps in-to the base part. This locking system is avibration-proof connection between pro-tective module and base part of the device.

Conclusion Telecommunication networks and sig-

nalling networks are endangered due toclose, remote and direct lightning effects[10]. The interference to be expected on

the cable is specified in various sets of re-gulation such as CLC/TS 61643-22:2005-09 [2] and IEC 62305-1 to -4 [3-6]. Ap-propriately dimensioned surge protectivedevices (SPDs) can protect the connectedIT equipment thus increasing systemavailability. In order to be able to assignan SPD to the IT equipment, a marking ofSPD classes for the Yellow/Line productline has been developed. This marking to-gether with the IT equipment documen-tation provides precise information aboutthe question whether SPD and IT equip-ment correspond to each other – i.e. ifthey are energy-coordinated to each other.

SPDs have to be inspected just like theIT equipment to be protected. SPDs withintegrated LifeCheck enable fast and easy testing as the SPD module does nothave to be removed from the base part ofthe SPD for testing. Furthermore Life-Check cannot only detect downtime ofthe protective circuit, but also an impend-ing overload. IT-based SPDs such asBLITZDUCTOR XT combine maximumpossible safety according to the currentstandardisation and easy handling whentesting and maintaining with a functionaland space-saving design. Thus, retrofit-ting can be as cost-effective as reinstal-lation of systems.

References[1] IEC 61643-21:2000-09 Low voltage

surge protective devices – Part 21: Surgeprotective devices connected to telecom-munications and signalling networks –Performance requirements and testingmethods. Genf/Schweiz: Bureau Centralde la Commission Electrotechnique Inter-nationale (ISBN 2-8318-5365-6)

[2]CLC/TS 61643-22:2005-09 (pre-standard) Low-voltage surge protectivedevices – Part 22: Surge protective de-vices connected to telecommunicationsand signalling networks – Selection andapplication principles. Genf/Schweiz: Bu-reau Central de la Commission Electro-technique Internationale

[3] IEC 62305-1:2006-01; Protectionagainst lightning – Part 1: General prin-ciples. Berlin Offenbach: VDE VERLAG

[4] IEC 62305-2:2006-01; Protectionagainst lightning – Part 2: Risk Manage-ment. Berlin Offenbach: VDE VERLAG

[5] IEC 62305-3:2006-01; Protectionagainst lightning – Part 3: Physical da-mage to structures and life hazard. Ber-lin Offenbach: VDE VERLAG

[6] IEC 62305-4:2006-01; Protectionagainst lightning – Part 4: Electrical andelectronic systems within structures. Ber-lin Offenbach: VDE VERLAG

[7] IEC 61643-1:1998-02; Low-voltagesurge protective devices – Part 11: Surgeprotective devices connected to low-vol-tage power systems – Requirements andtests. Berlin Offenbach: VDE VERLAG

[8] IEC 61000-4-5:2005-11; Electro-magnetic compatibility (EMC) – Part 4-5:Testing and measurement techniques –Surge immunity test Berlin Offenbach:VDE VERLAG

[9] Ackermann, G. (Hrsg.); Hönl, R.(Hrsg.) u. a.: Schutz von IT-Anlagen ge-gen Überspannungen [Protection of IT sys-tems against surges; published in German],Berlin Offenbach: VDE VERLAG, 2006

6 Heft 2/2007 •

Fig. 6: Testing SPDs by means of a portable test device and LifeCheck sensor

Fig. 7: Exchange of double-stack terminalblocks against Blitzductor XT while requiringthe same amount of space

Components & Periphery

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