DEHN - Lighting Protection Guide

6.1 Equipotential bonding for metalinstallations

Equipotential bonding according to IEC 60364-4-41 and IEC 60364-5-54

Equipotential bonding is required for all newlyinstalled electrical power consumer’s installations.Equipotential bonding according to IEC 60364series removes potential differences, i.e. preventshazardous touch voltages between the protectiveconductor of the low voltage electrical power con-sumer’s installations and metal, water, gas andheating pipes, for example.

According to IEC 60364-4-41, equipotential bond-ing consists of themain equipotential bonding (in future: protectiveequipotential bonding)and the supplementary equipotential bonding (in future:supplementary protective equipotential bonding)Every building must be given a main equipotentialbonding in accordance with the standards statedabove (Figure 6.1.1).The supplementary equipotential bonding isintended for those cases where the conditions fordisconnection from supply cannot be met, or forspecial areas which conform to the IEC 60364 seriesPart 7.

www.dehn.de LIGHTNING PROTECTION GUIDE 147

6. Internal lightning protection

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Foundation earth electrode

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Fig. 6.1.1 Principle of lightning equipotential bonding consisting of lightning and main equipotential bonding (in future: protective equipoten-tial bonding)

www.dehn.de148 LIGHTNING PROTECTION GUIDE

Main equipotential bondingThe following extraneous conductive parts have tobe directly integrated into the main equipotentialbonding:

⇒ main equipotential bonding conductor inaccordance with IEC 60364-4-41 (in future:earthing conductor)

⇒ foundation earth electrodes or lightning pro-tection earth electrodes

⇒ central heating system

⇒ metal water supply pipe

⇒ conductive parts of the building structure (e.g.lift rails, steel skeleton, ventilation and air con-ditioning ducting)

⇒ metal drain pipe

⇒ internal gas pipe

⇒ earthing conductor for antennas (in Germanyin DIN VDE 0855-300)

⇒ earthing conductor for telecommunicationsystems (in Germany in DIN VDE 0800-2)

⇒ protective conductors of the electrical installa-tion in accordance with IEC 60364 series (PENconductor for TN systems and PE conductorsfor TT systems or IT systems)

⇒ metal shields of electrical and electronic con-ductors

⇒ metal cable sheaths of high-voltage currentcables up to 1000 V

⇒ earth termination systems for high-voltagecurrent installations above 1 kV according toHD 637 S1, if no intolerably high earthing volt-age can be dragged.

Normative definition in IEC 60050-826 of an extra-neous conductive component:A conductive unit not forming part of the electri-cal installation, but being able to introduce electricpotential including the earth potential.Note: Extraneous conductive components alsoinclude conductive floors and walls, if an electricpotential including the earth potential can beintroduced via them.The following installation components have to beintegrated indirectly into the main equipotentialbonding via isolating spark gaps:

⇒ installations with cathodic corrosion protec-tion and stray current protection measures inaccordance with EN 50162

⇒ earth-termination systems of high-voltage cur-rent installations above 1 kV in accordancewith HD 637 S1, if intolerably high earthingpotentials can be transferred

⇒ railway earth for electric a.c. and d.c. railwaysin accordance with EN 50122-1 (railway lines ofthe Deutsche Bahn may only be connectedupon written approval)

⇒ measuring earth for laboratories, if they areseparate from the protective conductors

Figure 6.1.1 shows the terminals and the respectivecomponents of the main equipotential bonding.

Design of the earth-termination system forequipotential bondingThe electrical low-voltage consumer’s installationrequiring certain earthing resistances (disconnec-tion conditions of the protective elements) and thefoundation earth electrode providing good earth-ing resistances at cost-effective installation, thefoundation earth electrode is an optimal andeffective complement of the equipotential bond-ing. The design of a foundation earth electrode isgoverned in Germany by DIN 18014, which, forexample requires terminal lugs for the earthingbusbar. More exact descriptions and designs of thefoundation earth electrode can be found in Chap-ter 5.5.

If a foundation earth electrode is used as lightningprotection earth electrode, additional require-ments may have to be considered; they can be tak-en from Chapter 5.5.

Equipotential bonding conductors (in future: pro-tective bonding conductors)Equipotential bonding conductors should, as longas they fulfil a protective function, be labelled thesame as protective conductors, i.e. green/yellow.Equipotential bonding conductors do not carryoperating currents and can therefore be eitherbare or insulated.The decisive factor for the design of the mainequipotential bonding conductors in accordancewith IEC 60364-5-54 and HD 60364-5-54 is the crosssection of the main protective conductor. The mainprotective conductor is the one coming from thesource of current or from the service entrance boxor the main distribution board.


In any case, the minimum cross section of the mainequipotential bonding conductor is at least 6 mm2

Cu. 25 mm2 Cu has been defined as a possible max-imum.The supplementary equipotential bonding (Table6.1.1) must have a minimum cross section of 2.5mm2 Cu for a protected installation, and 4 mm2 Cufor an unprotected installation.

For earth conductors of antennas (according to IEC60728-11 (EN 60728-11)), the minimum cross sec-tion is 16 mm2 Cu, 25 mm2 Al or 50 mm2 steel.

Equipotential bonding barsEquipotential bonding bars are a central compo-nent of equipotential bonding which must clampall the connecting conductors and cross sectionsoccurring in practice to have high contact stability;it must be able to carry current safely and have suf-ficient corrosion resistance.DIN VDE 0618-1: 1989-08 (German standard) con-tains details of the requirements on equipotentialbonding bars for the main equipotential bonding.It defines the following connection possibilities asa minimum:

⇒ 1 x flat conductor 4 x 30 mm or round conduc-tor Ø 10 mm

⇒ 1 x 50 mm2

⇒ 6 x 6 mm2 to 25 mm2

⇒ 1 x 2.5 mm2 to 6 mm2

These requirements on an equipotential bondingbar are met by K12 (Figure 6.1.2).

This standard also includes the requirements forthe inspection of clamping units of cross sectionsabove 16 mm2 with regard to the lightning currentampacity. Reference is made therein to the testingof the lightning protection units in accordancewith EN 50164-1.If the requirements in the previously mentionedstandard are met, then this component can also beused for lightning equipotential bonding in accor-dance with IEC 62305-1 to 4 (EN 62305-1 to 4).

Terminals for equipotential bondingTerminals for equipotential bonding must providea good and permanent contact.

Main equipotential bonding Supplementary equipotential bonding

Normal 0.5 x cross section of thelargest protective conduc-tor of the installation

between two bodies 1xcross section of the small-er protective conductor

between a body and anextraneous conductivepart

0.5 x cross section of theprotective conductor

Minimum 6 mm2 with mechanicalprotection

2.5 mm2 Cu or equivalentconductivity

without mechanicalprotection

4 mm2 Cu or equivalentconductivity

Possible limit 25 mm2 Cu or equivalentconductivity

− −

Table 6.1.1 Cross sections for equipotential bonding conductors

Fig. 6.1.2 K12 Equipotential bonding bar, Part No. 563 200


Integrating pipes into the equipotential bondingIn order to integrate pipes into the equipotentialbonding, earthing pipe clamps corresponding tothe diameters of the pipes are used (Figures 6.1.3and 6.1.4).Pipe earthing clamps made of stainless steel, whichcan be universally adapted to the diameter of thepipe, offer enormous advantages for mounting(Figure 6.1.5).These pipe earthing clamps can be used to clamppipes that are made of different materials (e.g.steel, copper and stainless steel). These compo-nents allow also a straight-through connection.Figure 6.1.6 shows equipotential bonding of heat-ing pipes with straight-through connection.

Test and inspection of the equipotential bondingBefore commissioning the electrical consumer’sinstallation, the connections must be inspected toensure their faultless condition and effectiveness.A low-impedance conductance to the various partsof the installation and to the equipotential bond-ing is recommended. A guide value of < 1 Ω for theconnections at equipotential bonding is consid-ered to be sufficient.

Supplementary equipotential bonding

If the disconnection conditions of the respectivesystem configuration can not be met for an instal-lation or a part of it, a supplementary local equipo-tential bonding is required. The reason behind isto interconnect all simultaneously accessible partsas well as the stationary operating equipment andalso extraneous conductive parts. The aim is tokeep any touch voltage which may occur as low aspossible.

Moreover, the supplementary equipotential bond-ing must be used for installations or parts of instal-lations of IT systems with insulation monitoring.

The supplementary equipotential bonding is alsorequired if the environmental conditions in specialinstallations or parts of installations mean a partic-ular risk.

The IEC 60364 series Part 7 draws attention to thesupplementary equipotential bonding for opera-tional facilities, rooms and installations of a partic-ular type.

These are , for example,

⇒ IEC 60364-7-701 Rooms with bathtub or show-er

⇒ IEC 60364-7-702 Swimming pools and otherbasins

⇒ IEC 60364-7-705 For agricultural and horticul-tural premises

The difference to the main equipotential bondingis the fact that the cross sections of the conductorscan be chosen to be smaller (Table 6.1.1), and alsothis supplementary equipotential bonding can belimited to a particular location.

Fig. 6.1.3 Pipe earthing clamp,Part No. 408 014



Fig. 6.1.6 Equipotential bonding with straight-through connection


6.2 Equipotential bonding for lowvoltage consumer’s installations

Equipotential bonding for low voltage consumer’sinstallations as part of the internal lightning pro-tection, represents an extension of the main equi-potential bonding (in future: protective equipo-tential bonding) according to IEC 60364-4-41 (Fig-ure 6.1.1).In addition to all conductive systems, this also inte-grates the supply conductors of the low voltageconsumer’s installation into the equipotentialbonding. The special feature of this equipotentialbonding is the fact that a tie-up to the equipoten-tial bonding is only possible via suitable surge pro-tective devices. The demands on such surge protec-tive devices are described more detailed in AnnexE subclause 6.2.1.2 of IEC 62305-3 (EN 62305-3) aswell as in subclause 7 and Annexes C and D of IEC62305-4 (EN 62305-4).Analogous to the equipotential bonding with met-al installations (see Chapter 6.1), the equipotentialbonding for the low voltage consumer’s installa-tion shall also be carried out immediately at thepoint of entry into the object. The requirementsgoverning the installation of the surge protectivedevices in the unmetered area of the low voltageconsumer’s installation (main distribution system)are described in the directive of the VDN (Associa-tion of German Network Operators) “Surge pro-tective devices Type 1. Directive for the use ofsurge protective equipment Type 1 (up to nowClass B) in main distribution systems” (see sub-clauses 7.5.2 and 8.1) (Figures 6.2.1 and 6.2.2).

6.3 Equipotential bonding for infor-mation technology installations

Lightning equipotential bonding requires that allmetal conductive components such as cable linesand shields at the entrance to the building shall beincorporated into the equipotential bonding so asto cause as little impedance as possible. Examplesof such components include antenna lines, (Figure6.3.1) telecommunication lines with metal conduc-tors, and also fibre optic systems with metal ele-ments. The lines are connected with the help ofelements capable of carrying lightning current(arresters and shielding terminals). A convenientinstallation site is the point where cabling going

Fig. 6.2.1 DEHNbloc NH lightning current arrester installed in a bus-bar terminal field of a meter installation (refer to Fig. 6.2.2)

Fig. 6.2.2 DEHNventil ZP combined arrester directly snapped on thebusbars in the terminal field of the meter cabinet


outside the building transfers to cabling inside thebuilding. Both the arresters and the shielding ter-minals must be chosen to be appropriate to thelightning current parameters to be expected.In order to minimise induction loops within build-ings, the following additional steps are recom-mended:

⇒ cables and metal pipes shall enter the buildingat the same point

⇒ power lines and data lines shall be laid spatial-ly close but shielded

⇒ avoiding of unnecessarily long cables by layinglines directly

Antenna installations:For reasons connected with radio engineering,antenna installations are generally mounted in anexposed location. Therefore they are more affect-ed by surges, especially in the event of a directlightning strike. In Germany they must be integrat-

ed into the equipotential bonding in accordancewith DIN VDE 0855 Part 300 (German standard)and must reduce the risk of being affectedthrough their design, (cable structure, connectorsand fittings) or suitable additional measures.Antenna elements that are connected to an anten-na feeder and cannot be connected directly to theequipotential bonding, as this would affect theirfunctioning, should be protected by arresters.

Expressed simply, it can be assumed that 50 % ofthe direct lightning current flows away via theshields of all antenna lines. If an antenna installa-tion is dimensioned for lightning currents up to100 kA (10/350 μs) (Lightning Protection Level III(LPL III)), the lightning current splits so that 50 kAflow through the earth conductor and 50 kA viathe shields of all antenna cables. Antenna installa-tions not capable of carrying lightning currentsmust therefore be equipped with air-terminationsystems in whose protection area the antennas are

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Fig. 6.3.1 Lightning equipotential bonding with isolated air-termina-tion system, type DEHNconductor, for professional anten-na systems according to IEC 62305-3 (EN 62305-3)


located. Choosing a suitable cable, the respectivepartial lightning current share must be determinedfor each antenna line involved in down conduct-ing. The required cable dielectric strength can bedetermined from the coupling resistance, thelength of the antenna line and the amplitude ofthe lightning current.

According to the current standard IEC 62305-3 (EN62305-3), antenna installations mounted on build-ings can be protected by means of

⇒ air-termination rods

⇒ elevated wires

⇒ or spanned cables

In each case the separation distance s must bemaintained in the areas protected against light-ning strikes.The electrical isolation of the lightning protectionsystem from conductive components of the build-ing structure (metal structural parts, reinforce-ment etc.), and the isolation from electric lines inthe building, prevent partial lightning currentsfrom penetrating into control and supply lines andhence protect sensitive electrical and electronicdevices from being affected or destroyed (Figure6.3.1 and Figure 6.3.2).

Fibre optic installations:Fibre optic installations with metal elements cannormally be divided into the following types:

⇒ cables with metal-free core but with metalsheath (e.g. metal vapour barrier) or metalsupporting elements

⇒ cables with metal elements in the core andwith metal sheath or metal supporting ele-ments

⇒ cables with metal elements in the core, butwithout metal sheath.

For all types of cable with metal elements, the min-imum peak value of the lightning current, whichadversely affects the transmission characteristics ofthe optical fibre, must be determined. Cables capa-ble of carrying lightning currents must be chosen,and the metal elements must be connected to theequipotential bonding bar either directly or via anSPD.

⇒ Metal sheath: termination by means of shieldterminals e.g. SAK, at the entrance of thebuilding

⇒ Metal core: termination by means of earthingclamp e.g. SLK, near splice box

⇒ Prevention of potential equalising currents:connect indirectly via spark gap e.g. DEHNgapCS, base part BLITZDUCTOR CT, rather thandirectly

Telecommunication lines:Telecommunication lines with metal conductorsnormally consist of cables with balanced or coaxialcabling elements of the following types:

⇒ cables with no additional metal elements

⇒ cables with metal sheath (e.g. metal damp-proofing) and/or metal supporting elements

⇒ cables with metal sheath and additional light-ning protection reinforcement

The splitting of the partial lightning currentbetween IT lines can be determined using the pro-cedures in Annex E of IEC 62305-1 (EN 62305-1).The individual cables must be integrated into theequipotential bonding as follows:

a) Unshielded cables must be connected by SPDswhich are capable of carrying partial lightningcurrents. Partial lightning current of the linedivided by the number of individual wires =partial lightning current per wire.

b) If the cable shield is capable of carrying light-ning currents, the lightning current flows viathe shield. However, capacitive/inductive inter-ferences can reach the wires and make it nec-essary to use surge arresters. Requirements:

⇒ The shield at both ends must be connected tothe main equipotential bonding to be capableof carrying lightning currents (Figure 6.3.3).

Fig. 6.3.3 SAK shield connection system capable of carrying light-ning currents


⇒ In both buildings where the cable ends, thelightning protection zone concept must beapplied, and the active wires must be connect-ed in the same lightning protection zone (usu-ally LPZ 1)

⇒ If an unshielded cable is laid in a metal pipe,this must be treated like a cable with a cableshield which is capable of carrying lightningcurrents.

c) If the cable shield is not capable of carryinglightning currents, then:

⇒ for the terminal connected at both ends, theprocedure is the same as for a signal wire in anunshielded cable. Partial lightning current ofthe cable divided by the number of individualwires + 1 shield = partial lightning current perwire

⇒ if the shield is not connected at both ends, ithas to be treated as if it were not there; partiallightning current of the line divided by thenumber of individual wires = partial lightningcurrent per wire

If it is not possible to determine the exact wireload, it is recommendable to take the threatparameters from IEC 61643-22. For a telecommuni-cations line hence results a maximum load per wireof 2.5 kA (10/350 μs).

Of course not only the used SPD must be capableof withstanding the expected lightning currentload, but also the discharge path to the equipoten-tial bonding.By means of a multi-core telecommunications linefor example this can be demonstrated:

⇒ A telecommunications cable with 100 doublewires coming from LPZ 0A is connected in anLSA building distribution case and shall be pro-tected by arresters.

⇒ The lightning current load of the cable wasassumed to be 30 kA (10/350 μs)

⇒ The resulting symmetrical splitting of light-ning current to the individual wire is 30 kA/200 wires = 150 A/wire.

At first this means no special requirements to thedischarge capacity of the protective elements to beused. After the discharge elements have flownthrough, the partial currents of all wires add up to30 kA again to load in the downstream dischargepath, for example clamping frames, earthingclamps or equipotential conductors. To be safefrom any damage in the discharge path lightningcurrent tested enclosure systems can be used (Fig-ure 6.3.5).

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Fig. 6.3.4 Lightning equipotential bonding for connection of atelecommunications device BLITZDUCTOR CT (applicationpermitted by Deutsche Telekom)

Fig. 6.3.5 DEHN equipotential bonding enclosures (DPG LSA) forLSA-2/10 technology, capable to carry lightning current

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