6. Internal lightning protection
6.1 Equipotential bonding for metal
installations
Equipotential bonding according to IEC 60364-441 and IEC 60364-5-54
5
230/400 V
antenna
remote signalling system
equipotential bonding of bathroom
metal element going
through the building
(e.g. lift rails)
buried installation, operationally isolated (e.g. cathodic
protected tank installation)
Equipotential bonding is required for all newly
installed electrical power consumer’s installations.
Equipotential bonding according to IEC 60364
series removes potential differences, i.e. prevents
hazardous touch voltages between the protective
conductor of the low voltage electrical power consumer’s installations and metal, water, gas and
heating pipes, for example.
According to IEC 60364-4-41, equipotential bonding consists of the
main equipotential bonding (in future: protective
equipotential bonding)
and the
supplementary equipotential bonding (in future:
supplementary protective equipotential bonding)
Every building must be given a main equipotential
bonding in accordance with the standards stated
above (Figure 6.1.1).
The supplementary equipotential bonding is
intended for those cases where the conditions for
disconnection from supply cannot be met, or for
special areas which conform to the IEC 60364 series
Part 7.
1 Equipotential bonding bar
(main equipotential bonding,
in future: main earthing
terminal)
kWh
2 Foundation earth electrode
8
6
3 Connector
4
4 Lightning current arrester
1
5 Terminal
6
6 Pipe clamp
7 Terminal lug
to PEN
SEB
6
Z
gas
water
waste
water
IT system
insulating element
distribution
network
heating
6
8 Isolating spark gap
7
4
Z
terminal lug for external
lightning protection
foundation earth electrode /
lightning protection earth electrode
2
3
3
Fig. 6.1.1 Principle of lightning equipotential bonding consisting of lightning and main equipotential bonding (in future: protective equipotential bonding)
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LIGHTNING PROTECTION GUIDE 147
Main equipotential bonding
The following extraneous conductive parts have to
be directly integrated into the main equipotential
bonding:
⇒ earth-termination systems of high-voltage current installations above 1 kV in accordance
with HD 637 S1, if intolerably high earthing
potentials can be transferred
⇒ main equipotential bonding conductor in
accordance with IEC 60364-4-41 (in future:
earthing conductor)
⇒ railway earth for electric a.c. and d.c. railways
in accordance with EN 50122-1 (railway lines of
the Deutsche Bahn may only be connected
upon written approval)
⇒ foundation earth electrodes or lightning protection earth electrodes
⇒ central heating system
⇒ metal water supply pipe
⇒ measuring earth for laboratories, if they are
separate from the protective conductors
⇒ conductive parts of the building structure (e.g.
lift rails, steel skeleton, ventilation and air conditioning ducting)
Figure 6.1.1 shows the terminals and the respective
components of the main equipotential bonding.
⇒ metal drain pipe
Design of the earth-termination system for
equipotential bonding
The electrical low-voltage consumer’s installation
requiring certain earthing resistances (disconnection conditions of the protective elements) and the
foundation earth electrode providing good earthing resistances at cost-effective installation, the
foundation earth electrode is an optimal and
effective complement of the equipotential bonding. The design of a foundation earth electrode is
governed in Germany by DIN 18014, which, for
example requires terminal lugs for the earthing
busbar. More exact descriptions and designs of the
foundation earth electrode can be found in Chapter 5.5.
⇒ internal gas pipe
⇒ earthing conductor for antennas (in Germany
in DIN VDE 0855-300)
⇒ earthing conductor for telecommunication
systems (in Germany in DIN VDE 0800-2)
⇒ protective conductors of the electrical installation in accordance with IEC 60364 series (PEN
conductor for TN systems and PE conductors
for TT systems or IT systems)
⇒ metal shields of electrical and electronic conductors
⇒ metal cable sheaths of high-voltage current
cables up to 1000 V
⇒ earth termination systems for high-voltage
current installations above 1 kV according to
HD 637 S1, if no intolerably high earthing voltage can be dragged.
If a foundation earth electrode is used as lightning
protection earth electrode, additional requirements may have to be considered; they can be taken from Chapter 5.5.
Normative definition in IEC 60050-826 of an extraneous conductive component:
A conductive unit not forming part of the electrical installation, but being able to introduce electric
potential including the earth potential.
Note: Extraneous conductive components also
include conductive floors and walls, if an electric
potential including the earth potential can be
introduced via them.
The following installation components have to be
integrated indirectly into the main equipotential
bonding via isolating spark gaps:
Equipotential bonding conductors (in future: protective bonding conductors)
Equipotential bonding conductors should, as long
as they fulfil a protective function, be labelled the
same as protective conductors, i.e. green/yellow.
Equipotential bonding conductors do not carry
operating currents and can therefore be either
bare or insulated.
The decisive factor for the design of the main
equipotential bonding conductors in accordance
with IEC 60364-5-54 and HD 60364-5-54 is the cross
section of the main protective conductor. The main
protective conductor is the one coming from the
source of current or from the service entrance box
or the main distribution board.
⇒ installations with cathodic corrosion protection and stray current protection measures in
accordance with EN 50162
148 LIGHTNING PROTECTION GUIDE
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Main equipotential bonding Supplementary equipotential bonding
Normal
0.5 x cross section of the between two bodies
largest protective conductor of the installation
between a body and an
extraneous conductive
part
1xcross section of the smaller protective conductor
0.5 x cross section of the
protective conductor
Minimum
6 mm2
with mechanical
protection
2.5 mm2 Cu or equivalent
conductivity
without mechanical
protection
4 mm2 Cu or equivalent
conductivity
Possible limit
Table 6.1.1
25 mm2 Cu or equivalent −
conductivity
−
Cross sections for equipotential bonding conductors
In any case, the minimum cross section of the main
equipotential bonding conductor is at least 6 mm2
Cu. 25 mm2 Cu has been defined as a possible maximum.
The supplementary equipotential bonding (Table
6.1.1) must have a minimum cross section of 2.5
mm2 Cu for a protected installation, and 4 mm2 Cu
for an unprotected installation.
For earth conductors of antennas (according to IEC
60728-11 (EN 60728-11)), the minimum cross section is 16 mm2 Cu, 25 mm2 Al or 50 mm2 steel.
Equipotential bonding bars
Equipotential bonding bars are a central component of equipotential bonding which must clamp
all the connecting conductors and cross sections
occurring in practice to have high contact stability;
it must be able to carry current safely and have sufficient corrosion resistance.
DIN VDE 0618-1: 1989-08 (German standard) contains details of the requirements on equipotential
bonding bars for the main equipotential bonding.
It defines the following connection possibilities as
a minimum:
This standard also includes the requirements for
the inspection of clamping units of cross sections
above 16 mm2 with regard to the lightning current
ampacity. Reference is made therein to the testing
of the lightning protection units in accordance
with EN 50164-1.
If the requirements in the previously mentioned
standard are met, then this component can also be
used for lightning equipotential bonding in accordance with IEC 62305-1 to 4 (EN 62305-1 to 4).
Terminals for equipotential bonding
Terminals for equipotential bonding must provide
a good and permanent contact.
⇒ 1 x flat conductor 4 x 30 mm or round conductor 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 bonding
bar are met by K12 (Figure 6.1.2).
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Fig. 6.1.2 K12 Equipotential bonding bar, Part No. 563 200
LIGHTNING PROTECTION GUIDE 149
Fig. 6.1.3 Pipe earthing clamp,
Part No. 408 014
Fig. 6.1.4 Pipe earthing clamp,
Part No. 407 114
Integrating pipes into the equipotential bonding
In order to integrate pipes into the equipotential
bonding, earthing pipe clamps corresponding to
the diameters of the pipes are used (Figures 6.1.3
and 6.1.4).
Pipe earthing clamps made of stainless steel, which
can be universally adapted to the diameter of the
pipe, offer enormous advantages for mounting
(Figure 6.1.5).
These pipe earthing clamps can be used to clamp
pipes that are made of different materials (e.g.
steel, copper and stainless steel). These components allow also a straight-through connection.
Figure 6.1.6 shows equipotential bonding of heating pipes with straight-through connection.
Test and inspection of the equipotential bonding
Before commissioning the electrical consumer’s
installation, the connections must be inspected to
ensure their faultless condition and effectiveness.
A low-impedance conductance to the various parts
of the installation and to the equipotential bonding is recommended. A guide value of < 1 Ω for the
connections at equipotential bonding is considered to be sufficient.
Fig. 6.1.5 Pipe earthing clamp,
Part No. 540 910
Supplementary equipotential bonding
If the disconnection conditions of the respective
system configuration can not be met for an installation or a part of it, a supplementary local equipotential bonding is required. The reason behind is
to interconnect all simultaneously accessible parts
as well as the stationary operating equipment and
also extraneous conductive parts. The aim is to
keep any touch voltage which may occur as low as
possible.
Moreover, the supplementary equipotential bonding must be used for installations or parts of installations of IT systems with insulation monitoring.
The supplementary equipotential bonding is also
required if the environmental conditions in special
installations or parts of installations mean a particular risk.
The IEC 60364 series Part 7 draws attention to the
supplementary equipotential bonding for operational facilities, rooms and installations of a particular type.
These are , for example,
⇒ IEC 60364-7-701 Rooms with bathtub or shower
⇒ IEC 60364-7-702 Swimming pools and other
basins
⇒ IEC 60364-7-705 For agricultural and horticultural premises
Fig. 6.1.6 Equipotential bonding with straight-through connection
150 LIGHTNING PROTECTION GUIDE
The difference to the main equipotential bonding
is the fact that the cross sections of the conductors
can be chosen to be smaller (Table 6.1.1), and also
this supplementary equipotential bonding can be
limited to a particular location.
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6.2 Equipotential bonding for low
voltage consumer’s installations
Fig. 6.2.1 DEHNbloc NH lightning current arrester installed in a busbar terminal field of a meter installation (refer to Fig. 6.2.2)
Equipotential bonding for low voltage consumer’s
installations as part of the internal lightning protection, represents an extension of the main equipotential bonding (in future: protective equipotential bonding) according to IEC 60364-4-41 (Figure 6.1.1).
In addition to all conductive systems, this also integrates the supply conductors of the low voltage
consumer’s installation into the equipotential
bonding. The special feature of this equipotential
bonding is the fact that a tie-up to the equipotential bonding is only possible via suitable surge protective devices. The demands on such surge protective devices are described more detailed in Annex
E subclause 6.2.1.2 of IEC 62305-3 (EN 62305-3) as
well as in subclause 7 and Annexes C and D of IEC
62305-4 (EN 62305-4).
Analogous to the equipotential bonding with metal installations (see Chapter 6.1), the equipotential
bonding for the low voltage consumer’s installation shall also be carried out immediately at the
point of entry into the object. The requirements
governing the installation of the surge protective
devices in the unmetered area of the low voltage
consumer’s installation (main distribution system)
are described in the directive of the VDN (Association of German Network Operators) “Surge protective devices Type 1. Directive for the use of
surge protective equipment Type 1 (up to now
Class B) in main distribution systems” (see subclauses 7.5.2 and 8.1) (Figures 6.2.1 and 6.2.2).
6.3 Equipotential bonding for information technology installations
Fig. 6.2.2 DEHNventil ZP combined arrester directly snapped on the
busbars in the terminal field of the meter cabinet
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Lightning equipotential bonding requires that all
metal conductive components such as cable lines
and shields at the entrance to the building shall be
incorporated into the equipotential bonding so as
to cause as little impedance as possible. Examples
of such components include antenna lines, (Figure
6.3.1) telecommunication lines with metal conductors, and also fibre optic systems with metal elements. The lines are connected with the help of
elements capable of carrying lightning current
(arresters and shielding terminals). A convenient
installation site is the point where cabling going
LIGHTNING PROTECTION GUIDE 151
α α
isolated air-termination system
(DEHNconductor)
connection
equipotential bonding
feeding point
insulating pipe
isolated down conductor
(HVI-conductor)
230 V~
DATA
230 V~
α α
sealing unit
range
air termination tip
antenna
equipotential bonding
to BTS
s^
= 0.75 m in air
s^
= 1.5 m in brickwork
s = separation distance
earth-termination
system
Fig. 6.3.1 Lightning equipotential bonding with isolated air-termination system, type DEHNconductor, for professional antenna systems according to IEC 62305-3 (EN 62305-3)
Fig. 6.3.2 Isolated construction of a lightning protection system at a
cell site
outside the building transfers to cabling inside the
building. Both the arresters and the shielding terminals must be chosen to be appropriate to the
lightning current parameters to be expected.
In order to minimise induction loops within buildings, the following additional steps are recommended:
ed into the equipotential bonding in accordance
with DIN VDE 0855 Part 300 (German standard)
and must reduce the risk of being affected
through their design, (cable structure, connectors
and fittings) or suitable additional measures.
Antenna elements that are connected to an antenna feeder and cannot be connected directly to the
equipotential bonding, as this would affect their
functioning, should be protected by arresters.
⇒ cables and metal pipes shall enter the building
at the same point
⇒ power lines and data lines shall be laid spatially close but shielded
⇒ avoiding of unnecessarily long cables by laying
lines directly
Antenna installations:
For reasons connected with radio engineering,
antenna installations are generally mounted in an
exposed location. Therefore they are more affected by surges, especially in the event of a direct
lightning strike. In Germany they must be integrat-
152 LIGHTNING PROTECTION GUIDE
Expressed simply, it can be assumed that 50 % of
the direct lightning current flows away via the
shields of all antenna lines. If an antenna installation is dimensioned for lightning currents up to
100 kA (10/350 μs) (Lightning Protection Level III
(LPL III)), the lightning current splits so that 50 kA
flow through the earth conductor and 50 kA via
the shields of all antenna cables. Antenna installations not capable of carrying lightning currents
must therefore be equipped with air-termination
systems in whose protection area the antennas are
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located. Choosing a suitable cable, the respective
partial lightning current share must be determined
for each antenna line involved in down conducting. The required cable dielectric strength can be
determined from the coupling resistance, the
length of the antenna line and the amplitude of
the lightning current.
⇒ Metal core: termination by means of earthing
clamp e.g. SLK, near splice box
⇒ Prevention of potential equalising currents:
connect indirectly via spark gap e.g. DEHNgap
CS, base part BLITZDUCTOR CT, rather than
directly
According to the current standard IEC 62305-3 (EN
62305-3), antenna installations mounted on buildings can be protected by means of
Telecommunication lines:
Telecommunication lines with metal conductors
normally consist of cables with balanced or coaxial
cabling elements of the following types:
⇒ air-termination rods
⇒ cables with no additional metal elements
⇒ elevated wires
⇒ or spanned cables
In each case the separation distance s must be
maintained in the areas protected against lightning strikes.
The electrical isolation of the lightning protection
system from conductive components of the building structure (metal structural parts, reinforcement etc.), and the isolation from electric lines in
the building, prevent partial lightning currents
from penetrating into control and supply lines and
hence protect sensitive electrical and electronic
devices from being affected or destroyed (Figure
6.3.1 and Figure 6.3.2).
Fibre optic installations:
Fibre optic installations with metal elements can
normally be divided into the following types:
⇒ cables with metal-free core but with metal
sheath (e.g. metal vapour barrier) or metal
supporting elements
⇒ cables with metal elements in the core and
with metal sheath or metal supporting elements
⇒ cables with metal sheath (e.g. metal dampproofing) and / or metal supporting elements
⇒ cables with metal sheath and additional lightning protection reinforcement
The splitting of the partial lightning current
between IT lines can be determined using the procedures in Annex E of IEC 62305-1 (EN 62305-1).
The individual cables must be integrated into the
equipotential bonding as follows:
a)
Unshielded cables must be connected by SPDs
which are capable of carrying partial lightning
currents. Partial lightning current of the line
divided by the number of individual wires =
partial lightning current per wire.
b) If the cable shield is capable of carrying lightning currents, the lightning current flows via
the shield. However, capacitive/inductive interferences can reach the wires and make it necessary to use surge arresters. Requirements:
⇒ The shield at both ends must be connected to
the main equipotential bonding to be capable
of carrying lightning currents (Figure 6.3.3).
⇒ cables with metal elements in the core, but
without metal sheath.
For all types of cable with metal elements, the minimum peak value of the lightning current, which
adversely affects the transmission characteristics of
the optical fibre, must be determined. Cables capable of carrying lightning currents must be chosen,
and the metal elements must be connected to the
equipotential bonding bar either directly or via an
SPD.
⇒ Metal sheath: termination by means of shield
terminals e.g. SAK, at the entrance of the
building
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Fig. 6.3.3 SAK shield connection system capable of carrying lightning currents
LIGHTNING PROTECTION GUIDE 153
Telekom
c)
customer
TAE
IT installation
BLITZDUCTOR
BCT MLC BD 110
No.919 347
3 OUT 4
1 IN 2
BLITZDUCTOR CT
BCT MLC BD 110
5 kA (10/350 μs)
APL
Fig. 6.3.4 Lightning equipotential bonding for connection of a
telecommunications device BLITZDUCTOR CT (application
permitted by Deutsche Telekom)
If the cable shield is not capable of carrying
lightning currents, then:
⇒ for the terminal connected at both ends, the
procedure is the same as for a signal wire in an
unshielded cable. Partial lightning current of
the cable divided by the number of individual
wires + 1 shield = partial lightning current per
wire
⇒ if the shield is not connected at both ends, it
has to be treated as if it were not there; partial
lightning current of the line divided by the
number of individual wires = partial lightning
current per wire
If it is not possible to determine the exact wire
load, it is recommendable to take the threat
parameters from IEC 61643-22. For a telecommunications line hence results a maximum load per wire
of 2.5 kA (10/350 μs).
Of course not only the used SPD must be capable
of withstanding the expected lightning current
load, but also the discharge path to the equipotential bonding.
By means of a multi-core telecommunications line
for example this can be demonstrated:
⇒ A telecommunications cable with 100 double
wires coming from LPZ 0A is connected in an
LSA building distribution case and shall be protected by arresters.
⇒ The lightning current load of the cable was
assumed to be 30 kA (10/350 μs)
Fig. 6.3.5 DEHN equipotential bonding enclosures (DPG LSA) for
LSA-2/10 technology, capable to carry lightning current
⇒ In both buildings where the cable ends, the
lightning protection zone concept must be
applied, and the active wires must be connected in the same lightning protection zone (usually LPZ 1)
⇒ If an unshielded cable is laid in a metal pipe,
this must be treated like a cable with a cable
shield which is capable of carrying lightning
currents.
154 LIGHTNING PROTECTION GUIDE
⇒ The resulting symmetrical splitting of lightning current to the individual wire is 30 kA /
200 wires = 150 A / wire.
At first this means no special requirements to the
discharge capacity of the protective elements to be
used. After the discharge elements have flown
through, the partial currents of all wires add up to
30 kA again to load in the downstream discharge
path, for example clamping frames, earthing
clamps or equipotential conductors. To be safe
from any damage in the discharge path lightning
current tested enclosure systems can be used (Figure 6.3.5).
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