Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Communication, Navigation
& Surveillance Manual
Volume V
Lightning, Surge Protection and Earthing
System for CNS Installations
Version 2.0, April 2014
भारतीय विमानपत्तन प्राधिकरण
Airports Authority of India
संचार, दिक्चालन एव्म ननगरानी-प्रचालन एिं अनरु क्षण ननिे शालय
Directorate of CNS-OM
April 2014
Page 1/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
PREFACE
This is the Version 2.0 of CNS Manual Vol. V in the series of seven volumes of
CNS Manuals prepared and maintained by Directorate of CNS-OM, CHQ on behalf of
Airports Authority of India for the use and guidance of its executives and maintenance
personnel. The topics covered under these volumes are as under:Volume I – Maintenance of CNS Facilities
Volume II – Communication Procedures
Volume III – Siting Criteria of CNS Facilities
Volume IV – Flight Inspection of CNS Facilities
Volume V – Lightning & Surge Protection and Earthing System of CNS
Installations
Volume VI – Technical Specifications
Volume VII– Maintenance Schedules of CNS facilities
This volume contains the guidelines, recommended processes, procedures and
practices for protection of CNS installations from Lightning strikes, surge and transient
pulses which not only obliterate the expensive CNS/ATM systems but also disrupt Air
Navigations Services. The guidelines contained in this manual were framed by a duly
constituted committee by the competent authority for defining the standards and
recommended practices.
The guidelines, procedures and practices described in this volume, meticulously
followed by CNS maintenance personnel at Aeronautical Communication Stations will go
in a long way in protecting the vital CNS installations against damage and operational
disruptions occurring due to lightning and surges.
Views, comments and suggestions for improvement of this volume may be sent to
ED CNS-OM so as to incorporate them in the next Amendment/Version.
---------------------------
April 2014
Page 2/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Record of Amendments
No.
April 2014
Amendment Date
Incorporated on
Page 3/110
Incorporated by
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Table of Contents
Chapter 1
General
05
Chapter 2
General Requirements
08
Chapter 3
Lightning Protection System
10
Chapter 4
Earthing System
47
Chapter 5
Surge and Transient Protection System
66
Chapter 6
Earth Resistance Measurement
98
Chapter 7
SITC of Lightning, Surge Protection
and earthing System as part of turn key projects
100
Chapter 8
Maintenance Procedures of Lightning, Surge Protection
And earthing System
102
Chapter 9
Definitions and Acronyms
107
April 2014
Page 4/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter – 1
General
1.1 Title of the Document:
This document is identified as Communication, Navigation & Surveillance
Manual – Vol. V (CNSM- Vol .V) Version 2.0 “Lightning, Surge Protection and Earthing
System for CNS Installations.”
1.2 Scope of this Document:
This document mandates standard lightning protection, transient protection, surge
protection, grounding, bonding and shielding configurations to be provided for
CNS/ATM Automation facilities which are in operation at various airports.
1.3 Purpose of this Document:
Purpose of this document is to provide information and guidelines for
provisioning of Lightning, Surge Protection and Earthing System of CNS facilities, which
are essential for the provision of safe and efficient Air Navigation Services by Airports
Authority of India. It is published for the use and guidance of its CNS Maintenance
personnel.
1.4 Responsibility for documentation, review, amendments and publication:
1.4.1 The General Manager (Automation & Surveillance), AAI, CHQ is responsible
for development, review and amendments of CNS – Manuals Vol. V. He will ensure
that the information and guidelines pertaining to provisioning of Lightning, Surge
Protection and Earthing System of CNS facilities as detailed in this manual are in
conformity and current with respect to various National/International guidelines issued
on the subject.
April 2014
Page 5/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.4.2 The Executive Director (CNS-OM) is responsible for the approval of
documentation, subsequent amendments and publication of CNS-Manual.
1.5 Effective Date:
1.5.1 Effective date of the Manual is indicated at the bottom of the page.
1.5.2 New version, if any, will be indicated by the same date at the bottom of the page.
1.6 Change History:
1.6.1 This is Version 2.0 of CNS Manual Vol. V. Changes, if any, are indicated on
‘Record of Amendments and corrigenda page’. This Version 2.0 of the manual
supersedes Version 1.0 of this manual which was published in 2006.
1.5.2 Amendments – Documentation being inserted in the Manual must contain
headers and footers that are consistent with those given in this document.
1.7 Control of the Manual:Directorate of CNS-OM will control this Manual electronically through AAI, ANS
web site “aaians.aero” and AAI Intranet “Infosaarthee”.
1.8
Distribution of the Manual:-
Directorate of CNS-OM may produce hard copies and control the distribution of these
Copies, as deemed appropriate.
1.9
Master Copy:-
An electronic and a hard master copy of each Chapter contained in the Manual will be
held and maintained by the CNS-OM Directorate.
April 2014
Page 6/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
1.10
Checking Currency of Manual:-
A current copy of the Manual will be published on AAI ANS web site “aaians.aero”
and AAI Intranet “Infosaarthee”.
1.11
Enquiries:Any suggestions, Comments and Enquiries/Clarifications regarding this document
should be addressed to:
Executive Director (CNS - OM),
Airports Authority of India,
Rajiv Gandhi Bhavan,
Safdarjung Airport, New Delhi – 110003.
Email: smmisns@aai.aero or edcom@aai.aero
Telephone: 011- 24652075
FAX
: 011- 24654142
---------------------
April 2014
Page 7/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter - 2
General Requirements
2.1 Scope:This document covers Lightning, Surge Protection, earthing & bonding systems to
be adopted for CNS/ATM equipment’s with solid state components which are more
susceptible to damage due to surges, transients and over voltages being encountered in the
system due to lightning, sub-station switching etc. The recommendations specifically
cover the following:(a) Protection of sensitive electronic CNS/ATM Automation systems from lightning
resulting from a lightning strike to the building or its associated services
installations.
(b) Protection of buildings or structures housing CNS facilities against lightning
strike.
(c) Protection of sensitive electronic CNS/ATM Automation systems from
lightning/induction surges and spikes resulting from a lightning strike, power
switching etc.
(d) Earthing and bonding system to be adopted for CNS/ATM Automation systems.
(e) Maintenance procedures/practices to be followed for maintenance of Lightning
April 2014
Page 8/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
2.2 References:2.2.1 The basic framework of guidelines in this Manual is provided by following
references:IS-2309
Code of protection for Lightning Protection
IS -3043
Code of practice for earthing
IS -5216
Safety procedures & practice in electrical work
IEC -62305
Protection against Lightning
IEC -61643
Low Voltage Surge Protective Devices
ANSI/UL 467
Grounding & Bonding Equipment
IEEE- 80
IEEE guide for Safety in AC sub-station grounding
IEEE - 837
Standard for qualifying permanent connections used
in sub-station grounding
2.2.2 In addition, many inputs have been taken from BS:7430, IEC-60364 and NFPA
780 etc..
2.2.3 For the details, wherever required, respective Code, Standard or Guidelines as
mentioned above may please be referred to.
--------------------------------
April 2014
Page 9/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter - 3
Lightning Protection
3.1 Introduction:3.1.1
The effects of lightning discharge can be catastrophic on any installation
on ground if it is not adequately protected. In today’s world, almost everything and
anything is being controlled and operated through technologies involving the use of
VLSI and other electronic circuits which are highly static sensitive. Therefore,
protecting this equipment’s from lightning discharges and induction surges is of
paramount importance to ensure high level of serviceability and operational
availability.
3.1.2
The protection of the structure from direct lightning is only half of the
work needed to be done. It is also required to protect the systems and equipment
installed within the structure from induction surges arising out of lightning activity,
which at times could be costlier than the structure. This demands a holistic view to be
taken to cover all the aspects of lightning and surge protection. The installation must
be correct using correct material, the air terminal should give the total coverage, the
earth terminal must be right, and the right type of down conductor should be correctly
installed. The surge protectors must be put at every vulnerable point of entry, planned
for restricting the rise of ground potential in case of lightning discharge must be taken
to safe guard the facility. An illustration which protects the building surges in power,
RF/Data cable etc in a typical CNS installation is depicted in Figure-3.1.
April 2014
Page 10/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure-3.1:
3.1.3 The basic framework of this standardization is provided by Indian Standard
document IS-2309 (Lightning Protection). In addition, many inputs have been taken
from IEC-62305, IS 3043 (for Earthing), IS 5216 (Safety procedures & practices in
electrical work), BS:7430, IEEE 80, IEC-60364 , NFPA 780 etc.
3.1.4 Some details of the lightning phenomenon, characteristics of devices used in the
lightning and surge protection, methods to be used for CNS facilities Viz. LLZ, GP,
DVOR, Radar installations, Antenna etc. have also been included in the document.
3.2
Lightning Protection system :-
Lightning Protection comprises basically two types of protection:3.2.1 Direct Protection:-Protection of the structures, antenna and buildings against
the direct impact of lightning. The direct impact of lightning can cause serious
damages to the buildings, structures including fire accidents.
April 2014
Page 11/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.2.2 Indirect Protection: The indirect effects of lightning like surges and spikes will
cause malfunction and failure of sensitive electrical and electronic equipment through
induction. Appropriate surge and spike suppression mitigation techniques are to be
implemented accordingly.
3.3.3 For protection against both Direct and Indirect protection systems to work
efficiently, an effective earthing system offering a consistent low earth resistance is
essential. Hence protection system consists of three parts: -
3.3
-
External Lightning protection
-
Earthing system
-
Surge Protection
Lightning phenomenon
The phenomenon of discharge of static electricity generated in storm clouds to the
earth is lightning. It comes into existence when warm air masses containing sufficient
moisture are transported to greater altitudes. This transport can occur in number of ways.
Due to immense landmasses continent receives greater isolation and air near the ground
rise up. This creates up draught channels with vertical speed of more than 100 Kmph.
This warm air when gets mixed with colder air creates surges because of the opposite
charged nature of warm and cold air front. It occurs with generation of tremendous light,
heat, sound and pressure in the form of thunder.
3.3.1
Charge formation in clouds:-
Numerous theories have been advanced regarding the formation of charge centers,
charge separation within a cloud, and the ultimate development of lightning strokes.
One theory attributes charge separation to the existence of both positive and negative
ions in the air and the existence of a normal electric field directed toward the earth.
Large drops of water in the electric field are polarized, the upper sides acquiring a
negative charge and the lower sides a positive charge. As the polarized drops of water
April 2014
Page 12/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
fall due to gravity, the undersides (positive sides) attract negative ions, while no such
action occurs at the upper surfaces. As a result of this action, the drops accumulate
negative charge. Thus, the original charges, which were distributed at random and
produced an essentially neutral space charge, become separated. The large drops of
water carry the negative charges to the lower portion of the cloud, causing the lower
portion to be negatively charged and the upper portion to be positively charged.
Another theory is that the interaction of ascending wind currents in the leading
head of a cloud breaks up the water droplets causing the resulting droplets to be
positively charged and the air to be negatively charged. The positively charged water
droplets are unable to fall through the ascending wind currents at the head of the cloud,
which causes this portion of the cloud to be positively charged while the remaining
larger portion becomes negatively charged. Yet another theory suggests that there are
regions of subzero temperature within a cloud and the subsequent formation of ice
crystals is an essential factor in the explanation of the charge centers within clouds.
It has even been suggested that perhaps all of the physical phenomena postulated
in the various theories can occur. At best, the processes occurring within a cloud
formation that cause charge separation are complicated. The important fact to the
designing engineer is that a charge separation does occur in thunderstorm clouds.
Scientists have conducted various experiments using balloons equipped with electric
gradient measuring equipment to investigate typical charge distribution in
thunderclouds, and these experiments have shown that, in general, the main body of a
thundercloud is negatively charged and the upper part positively charged. A
concentration of positive charge also frequently exists in the base of the cloud. Such
charge distribution in a cloud causes an accumulation of charge of the opposite
polarity on the earth’s surface and on objects (e.g., trees, buildings, electric power
lines, structures, etc.) beneath the cloud. A typical charged cloud and the resulting
electric fields are shown in Figure 3.2(a) & (b). The electric fields shown in this
figure have been verified by data obtained by scientists from ground gradient
measuring equipment during the passage of storm clouds. The phenomenon of
April 2014
Page 13/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
discharge of static electricity generated in storm clouds to the earth is lightning.
Figure 3.2 (a)
Figure 3.2(b)
3.3.2
Lightning Mechanism:-
3.3.2.1 The charged cloud potential can assume any value in the range of
hundreds of mega Volts. The lightning stroke starts by the step by step descent
from the cloud of a leader stroke stepping some tens of meters at a time.
April 2014
Page 14/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.3.2.2 When the last step brings the tip of the leader sufficiently close to
earth, an upward streamer leaves the earth to join the tip of downward leader.
3.3.2.3 The initiation of this upward streamer depends on a critical field being
exceeded at the earth emission point and is also a function of the charge deposited
by the down-coming leader and any enhancement of the field caused by the
geometry of the earth.
3.3.2.4 The length of the upward streamer will be greater for greater charges
and hence high current flashes will start preferentially from high structures for
which the field enhancement is high.
3.3.2.5 This phenomenon is depicted in Figure 3.3 below:-
Figure 3.3(a)
Figure 3.3(b)
April 2014
Page 15/110
Figure 3.3(c)
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.4 Electrical characteristics of Lightning:3.4.2
Current in a Lightning Stroke: Current flow in an ‘average’
lightning flash can be accessed from the diagram below:-
Figure-3.4(a)
Fig 3.4(b)
Figure 3.4 (c)
April 2014
Page 16/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Further, from the above figures, folliwng four important parameters for lightning
protection technology can be obtained from the lightning current profiles:
The peak value of lightning current I;

The charge of the lightning current Qflash, comprising the charge of the short strike
Qshort and the charge of the long strike Qlong;

The specific energy W/R of the lightning current; and

The steepness di/dt of the lightning current.
Lightning current does not depend on load, in other words lightning current can be
considered as ideal current source if a load-independent active electric current flows
through conductive components, the amplitude of the current, and the impedance of the
conductive component the current flows through, help to regulate the potential drop
across the component flown through by the current. If a current is formed at a single point
on a homogeneously conducting surface, the well-known potential gradient area arises.
This effect also occurs when lightning strikes homogeneous ground.
Figure 3.5(a): Potential distribution of a lightning strike into homogeneous soil.
Higher the conductivity of the ground, flatter will be the shape of the potential
gradient area. If lightning strikes a building which is already equipped with a lightning
protection system, the lightning current flowing away via the earth-termination system
of the building gives rise to a potential drop across the earthing resistance R E of the
earth-termination system of the building (as shown in Figure 3.5(b)). In addition to
this threat any electrical installation near this building also has a potential threat due to
the differential earth resistance of the two sites. This difference in the presence of
April 2014
Page 17/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
lightning can induce a voltage of the order of 1000kV, which can harm the electrical
insulations nearby and can gravely endanger the network.
Figure 3.5 (b)
3.4.3
Typical lightning re-strike pattern
Usually lightning is continuous phenomenon of short duration i.e. there
may be multiple strike with random temporal variation with varying steepness
of lightning current (di/dt). Nature of this di/dt variation determines the height
of electromagnetically induced voltage as given in Figure 3.6.
Figure-3.6
April 2014
Page 18/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.4.4
Typical lightning current multiple re-strike pattern
Figure-3.7
3.4.5 Lightning Strike Electromagnetic Environmental Effects:-
Figure-3.8
3.4.6
The characteristics waveform of a lightning surge is as follows:-
Figure-3.9
April 2014
Page 19/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.5
The ‘Return stroke’: It is the most important part of a lightning flash
considering the resulting damages. This is that part of the flash in which a
charged cell in a thunder cloud is discharged to earth. The current in this return
stroke ranges from about 2,000 A to about 2,00,000 A and its distribution of
values is of the form which occurs frequently in nature, the so called
‘log/normal’ distribution. Out of all the lightning strokes, approximately 1 %
strokes exceed 200,000 A; 10% exceed 80,000 A; 50% exceed 28,000A; 90%
exceed 8,000 A and 99% exceed 3 000 A., hence, it is expected that only 1% of
lightning strikes are less than 3000A.
3.5.1
The current in most ground flashes is from the negatively charged
cells in the thunder cloud, and the flash current is, therefore, a negative flow from
cloud to ground; less frequently, strokes from a positive part of the cloud also
occur.
3.5.2 For either polarity, however, the current flow is unidirectional with a rise
time of less than 10 μs for the negative flash (but considerably longer for the
positive flash) and then decays to a low value, for a simple single stroke, in about
100 μs or less. Some flashes comprise two or more strokes which individually
conform to the description for a single stroke but which may be spaced in time 50
ms to 100 ms apart. The rare multi-stroke flash having more than 10 strokes may,
therefore, last for up to 1 second.
3.6
Voltage in a lightning strike: Before the flash takes place, the potential of the
charge cell may be estimated very roughly to be around 109V. It is reasonable,
therefore, to assume that the cloud potential is more than 100 MV. This potential is
high enough to ensure that the potentials sustained by whatever is struck will be
controlled by the product of current and impedance, because this product will never
be high enough in comparison with the cloud potential to modify the current
magnitude.
April 2014
Page 20/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.7
Effects of lightning
3.7.1 Electrical effect: As the current is discharged through the resistance of the
earth electrode of the Lightning Protection System, it produces a resistive voltage
drop which may momentarily raise the potential of the protective system to a high
value relative to true earth. It may also produce around the earth electrodes a high
potential gradient which is catastrophic to persons and animals. In the same
general manner, the inductance of the protective system must also be considered
because of the steep leading edge of the lightning pulse. The resulting voltage drop
in the protective system is, therefore, the combination of the resistive and inductive
voltage components.
3.7.2 Side Flash: The point of strike on the protective system may be raised to a
high potential with respect to adjacent metal. There is, therefore, a risk of flashover
from the protective system to any other metal on or in the structure. If such
flashover occurs, part of the lightning current is discharged through internal
installations, such as pipes and wiring, and so this flashover constitutes a risk to the
occupants and fabric of the structure.
3.7.3 Thermal effects: As far as it affects lightning protection, the effect of a
lightning discharge is confined to the temperature rise of the conductor through
which the current passes. Although the current is high, its duration is short, and the
thermal effect on the protective system is usually negligible. (This ignores the fusing
or welding effects on damaged conductors or those which were not adequate in the
initial installation.) In general, the cross- sectional area of a lightning conductor is
chosen primarily to satisfy the requirements of mechanical strength, which means
that it is large enough to keep the rise in temperature to 1°C. For example, with a 50
mm2 copper conductor, a severe stroke of 100kA with duration of 100μs dissipates
less than 400 J per meter of conductor resulting in a temperature rise of about 1°C.
The substitution of steel for copper results in a rise of less than 10°C.
April 2014
Page 21/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.7.4 Mechanical e f f e c t s : Where a high current is discharged along parallel
conductors at close proximity, or along a single conductor with sharp bends,
considerable amount of mechanical force is produced. Secure mechanical fittings
are, therefore, essential. A different mechanical effect exerted by a lightning flash is
due to the sudden rise in air temperature to 30,000 K and the resulting
explosive expansion of the adjacent air in the channel along which the charge is
propagated. This is because, when the conductivity of the metal is replaced by that
of an eructated path, the energy increases about one hundredfold, A peak power
of about 100 MW/m can be attained in the return stroke and the shock wave close to
this stroke readily dislodges tiles from a roof. Similarly, with a secondary flash
inside the building, the shock wave can result in damage to the building fabric.
3.8
Lightning damages to the installations:-
3.8.1 Lightning effects can be direct and/or indirect. Direct effects are from resistive
(ohmic) heating, arcing and burning. Indirect effects are more probable. They include
capacitive, inductive and magnetic behaviour. Lightning "prevention" or
"protection" (in an absolute sense) is impossible (IS 2309). A diminution of its
consequences, together with incremental safety improvements, can be obtained by the
use of a holistic or systematic hazard mitigation approach, described later.
3.8.2 A direct lightning attachment to an unprotected structure usually causes fire
and electrical damage. Occasionally explosive damage will occur if lightning strikes a
chimney or other porous structural component. Typically lightning strike to a roof or
protrusion causes arcing within the structure resulting ignition of structural materials.
Since lightning prefers the path of least impedance, it will tend to flow to the
electrical system and thence to earth, causing severe damage to the wiring.
3.8.3 There are many indirect electrical effects due to lightning strike. Flashover
occurs when lightning attaches to something which has a relatively high impedance
path to ground. The high impedance can develop a significant voltage on the object. If
April 2014
Page 22/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
this voltage exceeds the air breakdown value (approx 1 MV/m), the lightning may
jump from that object to a nearby grounded object. Common example is that of a man
injured through a nearby residential telephone line when it is energized by a distant
lightning strike.
3.8.4 Most lightning damages are noted for electronic equipment. A lightning
current pulse in a wire results induced voltage on the termination of other nearby
conductors. So called Surges are generated in secondary loops and metallic structures
mainly because of inductive coupling close to lightning current carrying conductors.
Surge current are generated with typical wave shape of T1/T2= 8/20 µs (i.e. rise time
8 µs and fall times 20 µs) with peak value of some kA up to some 10 kA. The high
voltage surge of a very small duration is potentially capable of damaging the
electronic circuitry.
3.9
Protecting the installations from lightning damages:3.9.1 It is impossible to stop or prevent the natural phenomenon of lightning
strikes [IS2309]. What can be done is to take measures so that the lightning energy
is given a safe passage to earth without harming the structure of interest. Universally,
the lightning rods are installed at topmost points of the structure and it is electrically
connected to a good earth using a good conductor to protect it from lightning
damages.
3.9.2 To protect the electronic equipment from lightning surges and transients, it is
required to shunt the current, block energy from travelling down the wire, filter
certain frequencies, clamp voltage levels or perform a combination of these tasks.
3.9.3 Voltage clamping devices capable of handling extremely high amperage of the
surge, as well as reducing the extremely fast rising edge (dv/dt & di/dt ) of the
transients are desired.
April 2014
Page 23/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.9.4 Adopting a fortress defence against surges and spikes is prudent i.e. protect the
AC mains panel, all relevant secondary distribution panels, incoming and outgoing
data and signal lines and also the incoming and outgoing RF cables.
3.10
Methodology for Direct Lightning Protection:-
3.10.1
Protection from direct lightning: The probability of direct lightning for
a normal structure is extremely low. However, depending on the functional
importance of a structure and its usage and its surrounding structures, all relatively
taller structures are required to be equipped with a lightning protection system. This
is to save the installation from damage and to save lives in case of lightning strike.
3.10.2
Importance for protection: Protection is very much essential because a
lightning strike can damage the fabric of the structure, start a fire and also can cause
loss of lives besides damaging the equipment.
3.11
Use of Air terminations:-
3.11.1
Air termination networks may consist of vertical or horizontal conductors
or combination of both types of conductors. Since the range of attraction is little
affected by the configuration of the conductor, vertical and horizontal arrangements
are equivalent.
3.11.2
Minimum dimension for air terminations are as follows:-
Components
Dimension
(in mm)
Air Termination
Aluminum, Copper & Galvanized steel
Aluminum & its alloy, Phosphor Bronze &
Area (mm2)
20 x 3
10.0 dia
60
78.54
19/2.14
19/2.14
6/4.72
70.0
70.0
100.0
Galvanized steel rods
Suspended Conductors
Stranded Aluminum
Stranded copper
Steel reinforced stranded Aluminum or
stranded galvanized steel
April 2014
Page 24/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.11.3
Simple Vertical conductor(s): Use of pointed air terminals on conical
top of a structure is simple and considered to be sufficient since its coverage is
generally adequate. Also putting horizontal air terminals on top of such structures
presents lot of challenges.
3.11.4
Horizontal conductor(s) for flat roofs: Putting horizontal air terminals
on flat roofs is simpler than putting vertical air terminals. Using vertical air
terminals for such structure will give inadequate coverage unless they are installed
in huge number.
3.12
Coverage of Air Terminations:-
3.12.1
Following diagram shows a simple vertical conductor and the zone of
protection in plan and elevation. The protective angle of any single component part
of an air termination network is 45 Deg. as shown in Figure 3.10:-
Figure-3.10
April 2014
Page 25/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.12.2
Between three or more vertical conductors, spaced at a distance not
exceeding twice their height, the equivalent protective angle may be taken as 60
Deg. to the vertical. As shown in Figure 3.11 below:-
Figure-3.11
Figure 3.11 shows four vertical conductors with the increased angle of protection.
However, it must be realized that although in suitable cases advantage may be
taken of the increased protective zone; this is only a statistical concept.
3.12.3
The zone of protection also extends to 45 Deg. of the Horizontal
conductor at each point of the conductor.
Figure-3.12 (a)
April 2014
Page 26/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure-3.12 (b)
Figure-3.12©
3.12.4 The Zone of Protection offered by an air termination network is considered to
be 45 Degree for heights up to 20meter. Above this height, the zone of protection is
determined by the “Rolling Sphere Method”. This involves rolling an imaginary
sphere of 60meter radius over a structure. The areas touched by the sphere are
deemed to require protection. On tall structures, this can obviously include the sides
of the building.
April 2014
Page 27/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure-3.13
Rolling sphere method to check coverage of air terminals
3.12.5 The maximum allowed spacing between horizontal conductors is 18 meter for
structures without special inherent risk.
3.13
Air Terminal Support :-
3.13.1
The materials used for installation should be non-corrosive and long
lasting.
3.13.2
The installation of air terminal on the tower should be such that the tip of the
air terminal is at the height of minimum 26 cm (10”) from the top level of the surface /
structure.
Figure-3.14
April 2014
Page 28/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.13.3
The support shall be securely bolted to other mast materials which are necessary
to enable the air termination and mast system to withstand maximum locally recorded
wind velocities.
Figure 3.15
3.13.4
Stainless steel Fasteners shall be used in the mounting structure at all the
places.
3.14
Typical Air Terminals for CNS Facilities:-
Typical air Terminals for lightning protection of CNS facilities are given below. It
must be understood that depending on the site conditions and other criteria like
maximum permissible height at the location, site specific requirement may vary.
3.14.1
DVOR/VOR installation:-
3.14.1.1 It is recommended to use vertical air terminals whose height and number
should be so adjusted that the antenna array is protected.
3.14.1.2
The Vertical air terminal on the collocated DME antenna should also be
taken into consideration while deciding required extent of coverage by the air
terminals for the VOR/DVOR antenna array.
April 2014
Page 29/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.14.1.3 The height of the conductors must give a clearance of at least 26 cm from
the nearest antenna to be protected by taking care that the antenna lays completely
within the zone of protection.
3.14.1.4 The monitor antenna should also be protected using a vertical air terminal.
The vertical conductors may be mechanically and electrically connected to the
counterpoise of the DVOR while ensuring that the electrical connection to the
earth is secured under all conditions.
3.14.1.5 All the sections of the counterpoise mesh must be bonded to each other
through long lasting bonding, taking care so that galvanic corrosion is controlled.
3.14.1.6 Hot dip galvanized iron-steel strip may be used for earthing of
counterpoise members to avoid chemical corrosion between copper strip and ironsteel.
3.14.1.7 Schematic Layout plan for DVOR LPS is shown in Fig. 3.16(a) & (b)
below:-
Figure-3.16(a)
April 2014
Page 30/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure-3.16(b)
3.14.2
Glide Path installation:-
3.14.2.1 It is recommended to use a vertical air terminal on top of the GP antenna
mast.
3.14.2.2 In fact, since the mast is metallic in nature, the vertical conductor may be
joined to the mast at its top. Proper metallic joints may be ensured between all
sections of the mast.
3.14.2.3 The GP equipment shelter will need a vertical air terminal if the shelter is
outside the protection zone of the mast air terminal. The height and position of the
shelter air terminal should be adjusted to protect the non-protected portion of the
shelter.
3.14.2.4 Schematic Layout plan for GP LPS is shown in figure 3.17 below:-
April 2014
Page 31/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure-3.17
3.14.2.5 The NF monitor antenna also needs to be protected by a vertical air
terminal on top of the monitor mast.
3.14.2.6 The collocated DME antenna needs to be provided with air terminal if it
is outside the protection zone of the GP antenna mast.
3.14.3
Localizer installation:-
3.14.3.1 It is recommended that a horizontal air terminal be used for the antenna
array. The horizontal conductor is to be supported using poles fixed on the two
ends of the antenna structure at least 26 cm away from the nearest antenna
structure.
3.14.3.2 The horizontal conductor should have a clearance of at least 26 cm from
the nearest antenna under all conditions of sag etc. The total antenna array must be
within the zone of protection.
3.14.3.3 he LLZ equipment shelter is required to be protected using vertical air
terminal of proper height and the positions should be so adjusted that the total
structure comes under its zone of protection.
April 2014
Page 32/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.14.3.4 The Far Field Monitor antenna also needs to be protected by a vertical air
terminal on top of the monitor mast. Height of air termination may be kept keeping
in view maximum permissible height at these locations.
3.14.3.5 The NF monitor may not require separate air termination for protection,
however RF cable must be provided with a coaxial surge protector.
3.14.3.6 Schematic Layout plan for LLZ LPS is shown in Figure 3.17 below:-
Figure-3.17
3.14.4 Marker Installation:3.14.4.1 Marker antenna installations are generally very near to ground, around 12
ft AGL. This may not necessitate putting lightning protection for this antenna. For
Lightning prone areas, however:
The LPS of the equipment building may be positioned to give the protection
coverage.

The LPS of any nearby mast (viz. collocated Locator Antenna) may be positioned
to give the protection coverage.

April 2014
If required an Air Terminal can also be positioned on the Marker mast.
Page 33/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.14.4.2. In any case, however, the Antenna RF cable must be provided with a
Coaxial Surge protector and standard protection may be ensured at the point of
entry into the equipment building (shelter).
3.14.5 NDB/Locator Installation
3.14.5.1 The NDB/LOC antennas which are not using self-radiating mast can be
protected from lightning by suitably installing Air Terminations on the masts.
However, the requirement of height for the lightning rods will be impracticably
high. A horizontal LA may also be impracticable.
3.14.5.2 The NDB/LOC antennas which are using self-radiating mast can be
protected from lightning by installing Lightning Rods on a suitable mast placed
nearby; however the requirement of height for the lightning rods will again be
impracticably high. A very near proximity of the Lightning rod mast may affect the
antenna performance.
3.14.5.3
Accordingly, it is suggested that no direct Lightning protection be
provided to these antennas and only coaxial surge protection to the RF Feeder
cables will suffice and suitable entry point protection at the entry of the building be
ensured.
3.14.6 DME Installation: Normally DME Antenna is protected by the LPS of the facility along with it is
collocated (i.e. DVOR/GP). However, if required,
separate air terminal is to be
provided for protecting DME if it is installed separately or is not within the lightning
protection zone of the collocated facility.
April 2014
Page 34/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.14.7
Surveillance facility (ASR/MSSR/SMR) installation:-
3.14.7.1 The antenna should be protected using horizontal air terminations. The
horizontal conductors are to be supported using poles installed by the side of the
antenna at least 26 cm away from the top of the nearest antenna structure.
3.14.7.2 The horizontal conductor should have a clearance of at least 26 cm from
the nearest antenna structure under all conditions of sag etc. The total antenna must
be protected.
3.14.7.3
The Radar building roof should be protected using a combination of
horizontal and vertical air terminations. The horizontal conductors on roofs should
form a 10m X 20m network and they should not be separated any further.
3.14.7.4 Schematic Layout plan for RADAR LPS (Lightning Protection System) is
shown in Figure 3.18 below:-
Figure 3.18
April 2014
Page 35/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.14.8 Lightning Protection for Antenna Masts/Towers etc.
3.14.8.1 Roof Mounted Antenna Masts
Unless it is a radiating or receiving part of the antenna, a metallic mast of a roofmounted antenna shall be bonded to a down conductor.
3.14.8.2 Pole Type Antenna Towers
Pole Type Towers shall be protected by at least one air terminal and have at least
one down conductor. This is to provide a lightning zone for all antennas located on
the tower.
3.14.8.3 Towers without Radomes [Control Tower/Radar Tower]
Protection shall be provided for large radar antennas by extending structural
members above the antenna and mounting the air terminal on top. The air terminal
shall be supported on the structural member. The down conductor from the air
terminal shall be connected to a perimeter conductor that forms a loop around the
perimeter of the tower platform. Down conductors shall be run from the perimeter
conductors to the Earthing System. All tower legs shall be bonded to the Earthing
System with a standard size copper conductor. The roof of the control tower is to be
protected from lightning as per Para 3.12.3.
3.14.7.4 Tower/Antenna Guying
All metallic guy wire systems without insulators shall be connected to the
Earthing System with a standard copper conductor to the Lightning Protection
system of the antenna if they are out of coverage of the Antenna lighting rod.
3.14.7.5 Waveguide, Coaxial Cables and Conduit Grounding
Waveguide, coaxial cable and conduit located on the tower and feeding into the
facility shall be separately bonded to a ground plate mounted on the tower or
directly to the earthing system. This bond shall be above and no greater than 2 feet
(0.6 m) from the transition bend (90 degree bend) near the tower’s base. Bond the
April 2014
Page 36/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
ground plate to the with a standard copper conductor. A separate bond shall be made
from the point of origin within tower structure of each coaxial cable or metallic
conduit to the metallic tower structure.
3.14.7.6 Staircase/Ladder Protection
The metallic access to the tower, i.e., staircase, ladder, etc., shall be bonded near its
base to the Earthing System with a standard copper conductor installed in a location
that avoids accidental tripping or striking that result in personnel jury. Where
staircase sections, platforms etc. are not welded together, bonding jumpers shall be
installed between them.
3.14.8 VSAT antenna or any other large aperture antenna:VSAT antenna or any other large aperture antenna not covered above are to be
protected against lightning by using method similar to in Para 3.14.7.
3.15
Down conductors, materials, size, etc :-
3.15.1
The down conductors play very important role in the LPS. The minimum
dimension for down conductors is as follows:Component
Aluminum, copper or galvanized steel
Dimension mm Area mm2
20 x 3
60.0
strip
Aluminum
and its alloy or galvanized steel 10.0 dia
78.54
rods
3.15.2
A good quality ISI mark copper strip 20 x 3 mm conductor should be
provided with suitable clamping/saddling to convey the captured energy by the air
terminal to the bonding system to a low impedance earth pit.
3.15.3 The metallic structure like that of a mast may be used as a down conductor
by ensuring electrical connectivity of the total structure to the earth.
April 2014
Page 37/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.15.4 The shaft of lift should not be used as a down conductor.
3.15.5
Where ever, it is practically impossible to inspect the connectivity of the of
air terminations on a regular basis, it is recommended to install two down conductors
separately to the air terminal. This will help in assessing the connectivity of the air
terminal to the earth by measuring the loop resistance between the two down
conductors.
3.15.6 The down conductor system must, wherever practicable, be directly routed
from the air termination to the earth termination network, and be symmetrically
placed around the outside walls of relevant structures, starting from the corners.
3.15.7
The number of down conductors should be one for each 30 Meter of the
perimeter of the protected structure.
3.15.8
On structures exceeding 20 Meter in height, down conductors should be
spaced at not more than 10 Meter apart.
3.15.9
It is important that each down conductor has its own independent earth.
3.15.10
The down conductor must be carefully routed to avoid side flashing. To
avoid side flashing, all metallic structures such as pipes, railings, metallic windows
etc., which are in contact with general mass of earth should be either isolated or
bonded to the down conductor, if the separation is less than 2 Meter. Minor items
like door hinges, metal gutter brackets, isolated reinforced beams may be
disregarded.
3.15.11
There should be no discontinuity in the down conductors, joints if any
should be preferably brazed. The test joints in the down conductor must conform to
the standards for corrosion free good contact.
April 2014
Page 38/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.15.12
Every precaution is to be taken to eliminate corrosion of the down
conductor, specifically at the joints and bonds.
3.15.13
Two down conductors must be used if the height of the installation is more
than 28 meters or the horizontal run of the down conductor is more than the vertical
height.
3.15.14
During maintenance check, perfect continuity of the air terminals to the
earth must be checked. Wherever there are practical difficulties to reach the air
terminal for such check, it is recommended to use two down conductors so that the
loop connectivity can be assessed.
3.15.15
Each down conductor should be provided with a test clamp for use during
testing.
3.15.16
Down Conductors should be provided for each Air Termination as per the
given standard (IS 2309) and should be connected to the common earth bus.
3.15.17
In the final 3 meters to the ground and where it is exposed to human
intervention, the down conductor shall be placed in a protective GI pipe, so as to
avoid mechanical damage and to increase human safely.
3.15.18
The down conductor shall be installed in accordance with the standard
procedure (may follow manufacturer’s instruction) and should not be subjected to
bends of less than 0.5 meters radius.
3.15.19
The down conductor shall be secured to the structure/building by metallic
fasteners to at least every Meter.
3.16
Routing of down conductor and prevention of side flashing:-
3.16.1
Re-entrant loops in the down conductor can produce high inductive
voltage drops which may help lighting discharge to jump across the open side of
April 2014
Page 39/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
the loop.
3.16.2
As a rough guide, the loop length must not be more than 8 times the
width of the open side of the loop.
Figure-3.19
Figure-3.20
3.16.3
The above requirement should be ensured even for a large re-entrant
loop.
3.17
Bonding - importance and application:3.17.1
Bonds have to join a variety of metallic parts of different shapes and
composition. Due to their varied use, there is the constant problem of corrosion due
to the metals involved.
April 2014
Page 40/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.17.2
The cross sectional area of the bond should not be less than the employed
main conductor.
3.17.3
A bond must be effective both mechanically and electrically and must be
protected from corrosion and erosion from the operating environment.
3.17.4
Following table gives metallic combinations for which galvanic potentials
are acceptable and the resultant corrosion is negligible :Aluminum
Copper
Stainless steel
Galvanized steel
Tin
alloys
Aluminum alloys
Copper
Stainless steel
OK
X
OK
OK
OK
350 mV
250 mV
250 mV
100 mV
X
OK
OK
X
OK
OK
OK
OK
OK
OK
X
OK
OK
OK
OK
OK
OK
OK
250 mV
150 mV
100 mV
Galvanized steel
Tin
3.17.5
OK
OK
In order to minimize contact corrosion of metal components in outdoor
applications, the electro chemical potential difference of unprotected connections
should not exceed 300 mV, and for well protected connection, it should not exceed
600 mV. Following Figure 3.21 shows the way to avoid galvanic corrosion:-
Figure-3.21
April 2014
Page 41/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.18
Precautions to be taken in bonding:-
Following points may be noted in this context:3.18.1
Aluminium is not allowed to be bonded to copper unless properly
isolated, for example using bimetal media.
3.18.2
Aluminium and copper should not be allowed in direct contact with
soil.
3.18.3
Copper can only be bonded to stainless steel and not to any other
iron/non-iron steel.
3.18.4
Tapes and gels etc. may be used to reduce ingress of moisture into the
bonds/joint, which is effective in reducing corrosion.
3.18.5
Metal entering or leaving a structure in the form of sheathing,
armouring or piping for gas, electric, water or any other service should be
bonded as directly as possible to the earth termination. This should be done near
to the point at which the service enters or leaves the structure.
3.18.6
Any joint other than welded one represents a discontinuity in the
current conducting system and is susceptible to failure.
3.18.7
A Lightning Protection System should have minimum number of joints.
3.18.8
Joints should be welded, brazed, riveted, crimped, bolted, screwed or
clamped in the order of preference.
3.18.9
Overlapping joints should not be less than 20mm for all type of
conductors.
Contact surface to be cleaned and inhibited from oxidation with
suitable non corrosive compound.
April 2014
Page 42/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.18.10
Different type of joints are shown in Figure 3.22 given below:-
Figure-3.22
3.18.11
Dissimilar metal contact must be overlapped for at least 40 mm with
the use of corrosion inhibitors as given in Figure -3.23 below:-
Figure-3.23
April 2014
Page 43/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.18.12
Each down conductor should be provided with a test joint, which will be
useful in isolating it from the earth during testing. It should preferably be a bolted
joint and easily accessible however, at the same time unauthorized accessibility
should be prevented.
3.19
Transient Event Counter:-
3.19.1
This optional device may be connected to the LPS for having an idea of
lightning strike to the system in highly lightning prone areas.
3.19.2
It shall be sensitive enabling to detection of a minimum current of 250A
(8/20 micro sec) and a max current of 100kA (10/350 micro sec).
3.19.3
It shall have a range of 0 to 99, suitable for cable cross section area up to
100 Sq mm capable to withstand a temperature range of -40 degree C to +60 deg. C.
3.19.4
The transient event counter shall be installed at less than 2.0M height from
ground.
3.20 EQUIPOTENTIAL PROTECTOR:3.20.1
In some rare circumstances, separate earthing systems are required to be
provided due to regulatory or special requirements. In such cases, the signal, power
and protective earth are separated thus becoming a potential cause of equipment
malfunction and damage due to significant difference in earth potential during a
lightning strike.
3.20.2
The Equipotential protector shall be used between the different Earth
systems which shall consist of a high capacity gas arrester which has a resistance of
more than 1Giga ohm under normal condition and thus exhibiting an open circuit with
low capacitance.
April 2014
Page 44/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.20.3
The protector shall be a very high performance gas filled arrester which
will momentarily conduct and in connecting the separate earths together there should
be a difference in earth potential. After the lapse of the transient impulses, it shall
reset automatically and return to its open circuit state.
3.20.4
It shall be totally maintenance free and capable to withstand more than
10000 operations thus guarantee a long working life.
3.20.5
The protector shall be housed in a robust and waterproof enclosure and
suitable to be used in any harsh environment.
3.20.6
It shall have following Features :

Long life, maintenance free, robust and waterproof.

Simple installation
3.20.7 The technical specifications of Equipotential Protector shall be as described
below:-
Clamping voltage
<380v
Voltage tolerance
+/- 20%
Max. surge rating
20- 150KA (8/20µs)
Impulse spark over Voltage
<600v (1KV/ µs)
Capacitance
<10pf
Insulation resistance
> 1G Ω
Humidity
0-95% (R.H)
Operating temperature
-40 to +80 deg C.
3.20.8 For more details regarding equipotential protector, Ref Annexure-2 – IEC
62305-3 Standard.
April 2014
Page 45/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
3.21 Lightning Protection System(LPS) - Earth termination network, types and
specifications:3.21.1
An earth electrode should be connected to each down conductor of LPS.
3.21.2
Each of these earths should have a resistance not exceeding the product
given by 10 Ω multiplied by the number of earth electrodes to be provided. For
example, for a system with 15 down conductors, the individual earth reading should
not be more than 10x15=150Ω. The whole lightning protective system, including
any ring earth, should have a combined resistance to earth not exceeding 10Ω
without taking account of any bonding.
3.21.3
A reduction of the resistance to earth to a value below 10Ω has the
advantage of further reducing the potential gradient around the earth electrode when
discharging lightning current. It also further reduces the risk of side flashing to metal
in or on a structure. Hence every effort shall be made to ensure as much low ground
resistance as possible.
3.21.4
The Earthing shall be provided/ made as per specifications given for
Earthing System in the manual.
----------------------------------------------------
April 2014
Page 46/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter - 4
Earthing Systems
4.1 Earthing:Lightning, Surges or Unintentional contact between an energized electric conductor
and the metal frame or structure that encloses it or an insulation failure in electrical
equipment’s etc., can cause dangerously high voltages in the electrical distribution
system. Under such circumstances, grounding provides an alternative low impedance path
and thereby minimizes damages. A good and an efficient earth ensure that all parts of
apparatus other than live parts shall be at earth potential that is zero at all the time.
The scope of this section shall cover the following:a)
Earthing electrode/station
b)
Earthing conductors
c)
Earthing of equipment and installation
The earthing resistance depends on:a)
Resistance of electrode
b)
Contact resistance between electrode and soil
c)
Resistance of soil between electrode surface and infinite earth.
Resistance of electrode and contact resistance between electrode and soil are very
small fraction of an ohm. Approximately 90 % of an earth resistance lies within 2 m
between electrode and earth.
Moreover, Earth conductivity is essentially electrolytic in nature and is affected by
moisture content of soil, its chemical composition and concentration of salt dissolved in
the contained water. It is also dependent on grain size and closeness in packing.
April 2014
Page 47/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.2
Selection of Earth Pit Site:-
Following is the order of preference for selecting an earth pit position.
4.3

Wet marshy ground

Clay/loamy soil with little sand

Clay/loamy soil with sand, gravel and stones

Damp and wet sand
Scope: This specification of earthing system describes in detail, the components
to be used and the procedure for constructing the earth system. The main purpose of this
is to maintain consistent low earth resistance value over the years without contaminating
the Ground water.
4.4
Components: The Earthing system shall consist of Earth Rods / plates and
conductive and eco-friendly backfill compound, Earth termination clamps and Earth Bus
Bar to facilitate connections to the equipment. The type earth electrode shall be any of the
following, as specified:-
4.5
(a)
Pipe / rod earth electrode ; (as per IS 3043)
(b)
Plate earth electrode; (as per IS 3043)
Methods of Implementations:-
The earthing can be implemented in four ways depending on the requirements, site and
ground conditions:4.5.1 Conventional earthing using copper plates as per IS 3043:4.5.1.1 Earth Pit of the Size of 1 meter diameter and 3 meter depth shall be
excavated, after depth of 3 meter the size of excavation shall be 900X300X900mm
depth.
4.5.1.2 Plate Electrodes shall be in vertical position.
4.5.1.3 PVC pipe for Watering shall be used of 40mm Diameter, length of 3m (
contain hole of 12mm Diameter in Zigzag manner starting from 15cm away from
bottom to 2 meter height ).
4.5.1.4 At bottom 150mm layer of salt and charcoal power shall be installed, then
Plate shall be installed.
April 2014
Page 48/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.5.1.5 Min 120 Kg each of charcoal powder and salt shall be used for each earthing
pit.
4.5.1.6 The plate/pipe electrode, as far as practicable, shall be buried below
permanent moisture level but in no case less than 2.5 meter below finished ground
level.
4.5.1.7 600 mm × 600 mm × 3.15 mm copper plate buried at a depth of 8 ft in
vertical position with the pit filled with alternate layers of charcoal and salt up to 4
ft from bottom.
4.5.1.8 The copper plates shall be connected to earth strip by riveting and brazing
at no less than two points and the joints shall be protected by heavy coat of bitumen.
4.5.1.9
Schematic diagram for copper plate earthing is shown in Figure 4.1.
Figure- 4.1
April 2014
Page 49/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.5.2
Earthing rods directly driven into the earth :-
4.5.2.1 The length of the electrode shall be either 1.22 meter or 2 meter or 3 meter
based on the application.
4.5.2.2 Electrodes used for neutral earthing and lightning protection earthing shall
be at least 3 meter long and for other applications, electrodes of at least 1.22 meter
or 2 meter length may be used.
4.5.2.3 Earthing System is depicted in Fig 4.2(a) and 4.2(b) below:-
Figure-4.2(a)
April 2014
Page 50/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure-4.2(b)
4.5.2.4
The combined earth rod length of a system should be no less than 9
meter whilst each individual earth rod should be no less than 1.5 meter in length.
Figure-4.3
April 2014
Page 51/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.5.3
4.5.3.1
Chemical earthing :A copper plate or copper coated rod, conventional earthing system
should be used as a rule. In general salt and charcoal is used as backfill material for
conventional earthing pits and these are eco-friendly.
4.5.3.2
In extreme conditions of rocky or sandy or dry condition where it is
difficult to achieve the desired performance of earthing terminals by conventional
system, chemical earthing may be employed.
4.5.3.3
The backfill material used in chemical earthing systems for soil
treatment shall be highly conductive and should be certified as non-polluting and
safe for use near potable ground water systems.
4.5.3.4
The ground conductivity enhancing backfill Material shall be a
compound having a low resistance in the range of 0.12 ohm/Meter as specified in
IEEE 80 (5 % of the Resistivity of Bentonite ), non-corrosive highly conductive
powdered material that improves grounding effectiveness, especially in areas of
high soil resistivity such as rocky and sandy areas.
4.5.3.5
This material shall be suitable to be installed in either slurry or dry
form. The backfill material shall confirm to the following specifications:

Shall be highly electrically conductive and non-soluble.

Shall not leach into ground.

Shall be electronically conductive (like in metals) and shall not depend on
moisture / salt for conduction

Shall have a resistivity of less than 0.12 ohm/meter

Shall be compatible with all copper grounding systems

Shall contain a corrosion inhibitor to mitigate corrosion of copper

Shall not contain hazardous chemicals
April 2014
Page 52/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------

Shall be certified to ANSI / NSF standard 60 as safe for use near potable
ground water resources

Shall not be affected by drought and shall be stable between -10˚ to + 50˚
C temperature.

Shall be suitable for any kind of soil

Where, the water table is high or runoff water is foreseen, the backfill
compound shall solidify as specified in BS: 7430. The compound shall set like
concrete to prevent erosion over a period of time. However under such condition
only conventional earthing system should be used.
NOTE:-Ref - BS7430 & IEEE80 where use of Carbon backfill compound for
obtaining low resistance and maintenance free earthing is clearly recommended
under specific conditions.
4.5.4
Horizontal / Lateral Earthing:-
Whenever it is not possible to excavate to a depth where the vertical earth electrodes
can be installed, the Lateral / Horizontal earthing method shall be adopted as follows:4.5.4.1
Three pits of 350 x 150 mm shall be dug to a depth of 3 feet and at a
distance of at least 2 meter from each other.
4.5.4.2
They can be laid either in a straight line formation or a triangular
formation depending on the space availability at site.
4.5.4.3
One copper bonded steel plate of 300 mm× 300 mm× 3 mm shall
be placed in each of the earth pits.
4.5.4.4
The earth pits shall be filled with the highly conductive and eco-
friendly backfill material up to 6 inches above the top of the plate.
April 2014
Page 53/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.5.4.5
These plates shall be interconnected using copper flat / strip of at
least 50 sq. mm cross sectional area. Such flat / strip shall be installed in a trench of
100 mm width at a depth of 600 mm (0.6m) from the ground level.
4.5.4.6
The entire trench shall be filled with the highly conductive and eco-
friendly backfill material in such a way that there is a minimum of 2 inches of
compound on the top and bottom of the interconnecting strip.
4.5
Earth Electrode Specifications:4.5.1
4.5.2
The electrodes shall be preferably in one piece of the desired length.
The electrode shall be a solid steel rod made of high tensile low carbon
steel and coated with molecularly bonded electrolytic copper on the outside (as per UL
467 or equivalent) . The Earth electrode shall conform to the following specifications :

Steel core: 600 MPa

The thickness of the copper coating shall be at least 250 microns.

Copper jacket should not crack on bending of earth rod

Copper: 99.9% pure electrolytic copper

Copper Structure: Very fine grain structure and highly ductile

Copper Bonding: Fully bonded with steel core

Nominal Diameter over Copper: 14.5mm

Threads: Rolled into copper M16x2

The electrode diameter shall be 14.2 mm dia .

Ends: Chamfer and Pointed (2mm and 6mm x 45deg)

The electrode should be able to carry a minimum short time current of 15
kA for one second.

Couplers should be made of brass

Clamps should be made of brass or stainless steel

Driving head or striker head should be of High tensile steel
April 2014
Page 54/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------

Driving tip should be of mild steel

The earth electrode shall carry standards marking and manufacturer’s
name.

Clamps and fixtures should be used in the earthing system to ensure
perfect and reliable contact.
4.5.3
Earth rod and accessories are depicted in Figure 4.4 below:-
Figure-4.4
NOTE: - Ref – IS-3043 & IEC-60364 where use of such electrodes are permitted &
the disadvantage of using plate electrodes are highlighted
April 2014
Page 55/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.6 Soil Treatment :Approximately 90 % of resistance between electrode and earth lies within a radius of
2m from the electrode. So, for soil treatment, to reduce the earth resistance, a shallow
basin, 0.5m around the top of the electrode, half a metre in radius is excavated. This
basin is then applied with artificial agents like NaCl, CaCl2, Na2CO3, CuSO4 ,salt, soft
coke, charcoal in suitable proportion. Then the basin is filled several times with water
for allowing it to percolate into the ground.
4.7 Earthing System Inspection Chamber: 4.7.1
A 300X300X300 mm (inside dimension) concrete box with smooth cement
plaster finish shall be provided on the top of the pit. A concrete lid, painted
black, approx. 50 mm. thick with pulling hooks, shall be provided to cover the
earth pit.
4.7.2
Care shall be taken regarding level of the floor surrounding the earth so that
the connector is not too deep in the masonry or projecting out of it.
4.7.3
On backside of the cover, date of the testing and average resistance value
shall be written with yellow paint on black background.
4.7.4
Alternatively prefabricated earthing inspection chambers may also be used.
These have precise dimension and better service life. They are convenient to
install and require low maintenance. A Polymer or CI cover shall be provided
on the top of the earth system. The prefabricated Earthing inspection chamber
should be light weight and suitable for extreme weather conditions.
4.7.5 Care shall be taken regarding Care shall be taken regarding level of the floor
surrounding the earth so that the connector is not too deep in the masonry or
projecting out of it.
April 2014
Page 56/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.7.6
Grounding test terminal box shall be installed at an appropriate location
suitable for testing the earth resistance.
4.7.7
Typical Inspection Chamber is shown in Figure 4.5 below:-
Figure 4.5- Inspection Chamber
4.8
Earthing Conductor: -
4.8.1 The earth conductors shall be fixed to the wall/columns etc., at every 500mm
with 10mm spacers. The total earthing system shall be mechanically and electrically
connected to provide independent path to earth.
4.8.2 If the conductor is protected from corrosion, the area of cross section for copper
conductor shall be more than 16 mm2.
4.8.3 If the conductor is not protected from corrosion, the area of cross section for
copper conductor shall be more than 25 mm2.
April 2014
Page 57/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.9
Earth Resistance:
The earth resistance of combined earth system (to be measured at EEB) shall be
less than or equal to 1 ohm, as per the requirement. It shall be measured by an approved
earth testing apparatus for individual earth pits. The procedure for measuring earth
resistance is given in Chapter- 6.
4.10 Equipotential Earth Bus bar and its connection to equipment’s & Surge
protection devices in the Equipment room: 4.10.1 Equipotential earth bus bars
4.10.1.1 There shall be one Equipotential earth bus bar for each of the equipment
room. The Equipotential earth bus bars located in individual equipment rooms shall
be termed as Sub Equipotential bus bars (SEEB). The Equipotential earth bus bar
connected to Class ‘B’ SPDs and the main earth pit shall be termed as Main
Equipotential earth bus bar (MEEB).
4.10.1.2 The EEBs shall have pre-drilled holes of suitable size for termination of
bonding conductors. The EEBs shall be insulated from the building walls. Each
EEB shall be installed on the wall with low voltage insulator spacers of height
60mm. The insulators used shall have suitable insulating and fire resistant
properties for this application. The EEBs shall be installed at the height of 0.5m
from the room floor surface for ease of installation & maintenance. All terminations
on the EEBs shall be by using copper lugs with spring washers.
4.10.2 Bonding Connections:4.10.2.1 To minimize the effect of circulating earth loops and to provide equipotential bonding, “star type” bonding connection is required. As such, each of the
SEEBs installed in the rooms shall be directly connected to MEEB using bonding
conductors. Also, equipment/racks in the room shall be directly connected to its SEEB.
The bonding conductors shall be bonded to their respective lugs by welding.
April 2014
Page 58/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.10.2.2 All connections i.e. routing of bonding conductors from equipment’s to
SEEB & from SEEBs to MEEB shall be as short and as direct as possible with min.
bends and separated from other wiring. However, connection from SPD to MEEB
shall be as short as possible and preferably without any bend.
4.10.2.3 Materials and dimensions of bonding components for connection of
individual equipment’s with Equipotential bus bar and earth electrode shall be as
given below:Component /Bonding
Material
Size
Main Equipotential earth bus Copper
300X25X6 mm (min.)
bar (MEEB)
Sub Equipotential earth bus Copper
150X25X6 mm (min.)
bar (SEEB)
Individual equipment’s to Multi-strand
SEEB using copper lugs
single
core 10 sq.mm
PVC insulated copper cable
with stainless steel nut and as per IS:694
bolts.
SEEB
to
MEEB
using Multi-strand
single
core 16 sq.mm
copper lugs with stainless PVC insulated copper cable
steel nut and bolts.
Surge
protection
(SPD)
to
as per IS:694
devices Multi-strand
MEEB
single
core 16sq.mm
using PVC insulated copper cable
copper lugs with stainless as per IS:694
steel nut and bolts.
MEEB
to
main
electrode.
earth Multi-strand
single
core 35sq.mm
PVC insulated copper cable
as per IS:694 (Duplicated)
Main earth pit to other earth Copper tape
25X2 mm
pit in case of loop earth
April 2014
Page 59/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.11 Markings for Earthing systems:4.11.1
Earth bars and terminals at all switch boards shall be marked permanently
as “E”.
4.11.2
Main earth terminal shall be marked safety earth – “DO NOT
DISCONNECT”.
4.11.3
All earth pit shall be identified properly i.e. by suitable nomenclature
identifying earth pit with the facility, Earth pit no etc.
4.12
Earthing System Requirement for CNS facilities:-
4.12.1
The electronic ground conductor shall be PVC insulated standard copper
wire of 22 mm² or larger. One such conductor shall run from each equipment area or
grouping of related electronic equipment and be terminated at the grounding test
terminal box. Electronic ground conductors shall not be interconnected except at the
common point.
4.12.2
Each cabinet and isolated item of electronic equipment shall be
individually connected to the electronic ground conductor by the shortest possible
route. The connecting jumper wire shall be 8 mm² or the size of the power feeder to the
electronic equipment cabinet, whichever is larger. In addition, cabinets which are
installed side-by-side shall be bonded together by copper wire jumpers, of 8 mm² or
larger.
4.12.3
Care shall be taken to assure that ground loops are not created
inadvertently.
April 2014
Page 60/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.13
COMMUNICATIONS CABLE TRAY SYSTEMS:-
4.13.1
Bond the metallic structures of one cable tray in each tray run following
the same path to provide 100 percent electrical continuity throughout this cable tray
systems as follows:4.13.1.1 Splice plates provided by the cable tray manufacturer can be used for
providing a ground bonding connection between cable tray sections when the
resistance across a bolted connection is 10 milliohms or less.
4.13.1.2 Install a standard (16 mm²) bonding jumper across each cable tray splice or
junction where splice plates cannot be used.
4.13.1.3 When cable tray terminations to cable rack, install standard 16 mm²
(bonding jumper between cable tray and cable rank pan.
4.14
Important points regarding Earthing System
4.14.1
Minimum dimensions for earth terminations are as follows :-
Component
Dia in mm
2
Area mm
Copper clad or galvanized steel rods.
17.2(with
232
For Copper clad steel rods, the core should be of low
minimum
2
carbon steel of tensile strength 700 N/mm ,(as per
of 3 meter)
491
Underwriters laboratories UL-467-2007)
99.9% electrolytic copper should be molecularly bonded
to the steel core and radial width of copper should not be
less than 0.25 mm.
length
25
804
32
4.14.2
Earth network / ring: A common earth termination network is
recommended for the lightning protective system and all other services.
4.14.3
The resistance to earth should, in this case, be the lowest value required
for any of the individual services. In other words, all the earth terminals that of
equipment, electrical power, lightning protective system, antenna, etc., are to be
connected together to form a common earth network.
April 2014
Page 61/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.14.4
One lightning protection system should consist of at least one plate earth
terminal and other earth electrodes made by driving copper rods of suitable type into
the ground.
4.14.5
No appreciable advantage in resistance reduction is gained by increasing
the diameter or surface of the driven electrode. Larger sizes become more difficult to
drive and are more expensive in materials.
4.14.6
Where deep driving of earth rods is not possible, a matrix arrangement of
rods coupled to one another by conductors can be used. If possible the earth rods must
be spaced at a distance at least twice their driven depth.
4.15
Importance of earth ring in reducing potential gradient:-
4.15.1
As the lightning current is discharged through the earth electrode, the
surrounding soil is raised for the duration of the discharge to a potential with respect
to the body of the earth. The resulting potential gradient is illustrated in Figure 4.6
and it is shown how its voltage gradient can be reduced by adding ring earth
electrodes to lower the effective earth resistance.
4.15.2
Such potential difference may be lethal to a person if it exceeds a few
thousand volts and to an animal if it exceeds a few hundred volts.
4.15.3
As this potential difference is a function of the product of the lightning
current and the resistance of the earth electrode, the importance of keeping the latter
as low as possible is evident. For practical purposes, a maximum value of 10Ω is
recommended.
4.15.4
The danger to persons within a structure is effectively reduced by the
presence of any floor other than that of earth or rock.
April 2014
Page 62/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.15.5
To reduce the voltage gradient in case of lightning, along ground surface
near to masts, towers and columns, the earth terminations of each lightning protective
system should be interconnected by a ring conductor.
4.15.6
This ring conductor should preferably be buried to a depth of at least 0.5m
unless other considerations, such as the need for bonding other objects to it or testing,
make it desirable to leave it exposed.
4.15.7
The ring conductor should be connected to the ring conductors of the
neighbouring structures.
Figure-4.6
April 2014
Page 63/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.16
Anti-corrosive measures (Importance thereof):-
Corrosion due to atmospheric, chemical, electrolytic or other causes is likely to
impair any part of the lightning protective system; therefore, suitable precautions as
mentioned below should be taken to prevent its occurrence:4.16.1
Due to the harmful corrosion which is likely to result, coke breeze should
not be allowed to come in contact with copper electrodes and salting of the ground in
the vicinity of any earth electrode should not be practiced.
4.16.2
In some cases if it is not possible to achieve earth’s resistance less than 1
ohm then all copper to copper joints shall be made by welding or brazing only Bolting
of joints shall not be accepted. The minimum distance by which these electrodes
should be separated is 3mtrs and maximally it can go up to twice of it i.e. 6mtrs.
4.16.3
Electrolytic corrosion between dissimilar metals: The contacts of
dissimilar metals unless the contact surfaces are kept completely dry and protected
against the ingress of moisture, is likely to initiate and accelerate corrosion.
4.16.4
The metal of lightning protection system must be compatible to the metals
of the structure over which it passes or makes contact with corrosion inhibitors may
be used if required.
4.16.5
Aluminium is prone to corrosion when in contact with cement and mortar
mixes.
4.16.6
Backfill compound if used for soil treatment shall provide anti corrosion
protection to the electrodes.
4.16.7
Fittings should be resistant to the corrosive agencies or be otherwise
suitably protected.
April 2014
Page 64/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
4.16.8
Joints and bonds may be protected with bitumen or embedded in plastic
compound according to the local conditions as shown in figure 4.7 below:-
Figure-4.8
-------------------------------------------------------
April 2014
Page 65/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter-5
Surge and Transient Protection Systems
5.1 Surge & Transient:- Surge is an overvoltage or over current of a short duration
occurring on a power line while transient is an overvoltage or over current pulse
occurring on a power, signal, control or data line.
The term “surge” is used to describe a transient overvoltage on a power line that
has duration of a few microseconds. A transient overvoltage can exceed the insulation
rating of electrical equipment causing degradation of insulation and immediate damage
to the equipment. Relatively low-amplitude transient over voltages applied repetitively on
the equipment will reduce its mean time before failure. The result will be that equipment
will have to be repaired more often, increasing operating costs.
5.2 Why Surge Protection is needed:5.2.1 Power surges can cause failure, permanent degradation, or temporary
malfunction of electronic devices and systems. The development of an effective Surge
Protection Device (SPD) is of paramount importance to manufacturers and users of
industrial electronic equipment.
5.2.2 Almost all manufacturers of industrial-type SPDs use metal–oxide varistors
(MOVs) in their design. MOVs are composed of a thin disk wafer of material (metal–
oxide) that has a known voltage breakdown characteristic. At low voltages, the MOV
conducts very little current (microamperes). As the voltage approaches breakdown,
the MOV then begins to conduct current. At voltages slightly above the break down,
large currents flow, effectively clamping the output voltage. This clamping feature
allows the higher voltage levels to be shunted to ground, preventing over voltages on
equipment.
April 2014
Page 66/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.2.3 Figure 5.1 and 5.2 below show the voltage waveform before and after an ideal
SPD:-
Figure 5.1 Voltage waveform before SPD.
Figure 5.2 Voltage waveform after an ideal SPD
April 2014
Page 67/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.2.4 Causes of Power Line Surges:The sporadic damped phenomena that occur in electrical systems are generally
described as transients and surges or in other words Power surges and transient over
voltages are due to the sudden change in the electrical conditions of a circuit and the
release of large amounts of energy stored in the inductance and capacitance elements
of the system. Sources of power surges can be external or internal to the facility.
5.2.4.1 External sources of transient over voltages can be the following:
Lightning.
 Switching (on/off) of capacitor banks, for power coefficient Correction.

Power-line disconnection and reconnection.

Transformer switching on/off.

Electrostatic discharges.

Power utility load switching.

Poor quality of power transmission and distribution grids.
5.2.4.2
5.3
Internal surges are caused by the operation of the following devices:-

circuit breakers or fuses;

electric motors, i.e., elevators;

air conditioners;

VSDs generators.
It is very important to note that the IS 3043 has specifically recommended the use
of surge protection systems to protect the sensitive equipment’s against over voltages
induced by lightning and switching surges.
April 2014
Page 68/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.4
Transient over voltages are generated due to:a) Whenever a lightning strikes directly / in the near vicinity;
b) As a consequence of different faults in the power system; and
c) Switching on and off of different loads etc.
d) Hence, it is very important to protect the sensitive electrical and electronic
equipment’s against these transient voltage surges.
5.5
The transient voltage surges are broadly classified into two types :-
5.5.1

Lightning Surges ( Handled by Class B or Type I SPDs); and

Switching surges ( Handled by Class C or Type II SPDs)
The lightning surges bring very high amount of destructive energy into the
system and hence, are potentially very dangerous. The Class B SPDs are designed to
handle the lightning current surges.
5.5.2
The switching surges are relatively frequent than the lightning surges.
Although they bring in relatively less energy into the system, however, they still are
strong enough to damage the sensitive electronics. The switching surges are handled
by the Class C SPDs.
5.5.3
Latest IEEE Guidelines express that lightning activity at a place can
induce surges due to Galvanic Coupling for about 1.7 km radius from the point of
impact. Hence, it is important to note, both the lightning and the switching surges can
come from outside of our power system and hence these surges need to be isolated at
the mains input point itself so it is important to put appropriate surge protection
devices to all the cables i.e. Power, Data, Remote Control, RF Cables or any other
devices which is likely to carry surge and which enters into a equipment room where
sensitive CNS/ATM systems are installed.
April 2014
Page 69/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.6
Methodology for surge protection:-
Surge mitigation technique suggests use of surge suppression devices for power and data
lines. The sole function of a good quality surge suppressor is to protect sensitive
electronic equipment from transient over voltages. It must limit transient over voltages to
a value that do not surpass the AC sine wave peaks by more than 30%.
5.6.1
A surge protector (or surge suppressor) is an appliance designed to
protect electrical devices from voltage spikes. A surge protector attempts to limit the
voltage supplied to an electric device by either blocking or shorting to ground any
unwanted voltages above a safe threshold.
5.6.2
The terms surge protection device (SPD), or the obsolescent term
transient voltage surge suppressor (TVSS), are used to describe electrical devices
typically installed in power distribution panels, process control systems,
communications systems, and other heavy-duty industrial systems, for the purpose of
protecting against electrical surges and spikes, including those caused by lightning.
5.7
Main performance parameters of a surge protector are as follows:5.7.1
Clamping voltage also known as the let-through voltage. This specifies
what spike voltage will cause the protective components inside a surge protector to
divert unwanted energy from the protected line. A lower clamping voltage indicates
better protection, but can sometimes result in a shorter life expectancy for the overall
protective system.
5.7.2
Joules rating: This number defines how much energy the surge protector
can theoretically absorb in a single event, without failure. Counter-intuitively, a lower
number may indicate longer life expectancy if the device can divert more energy
elsewhere and thus will need to absorb less energy. In other words, a protective device
April 2014
Page 70/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
offering a lower clamping voltage while diverting the same surge current will cause
more of the surge energy to be dissipated elsewhere in the system. Better protectors
exceed peak ratings of 1000 Joules and 40,000 Amperes. It is often claimed that a
lower Joule rating is undersized protection, since the total energy in harmful spikes can
be significantly larger than this. However, if properly installed, for every joule
absorbed by a protector, another 4 to 30 joules may be dissipated harmlessly into
ground. A MOV-based protector (described below in Para 4.8.1) with a higher letthrough voltage can receive a higher joule rating, even though it lets more surge
energy through to the device to be protected.
5.7.3
Response time: Surge protectors do not operate instantaneously; a slight
delay exists. The longer the response time, the longer the connected equipment will be
exposed to the surge. However, surges usually take around a few microseconds to
reach their peak voltage, and a surge protector with a nanosecond response time would
kick in fast enough to suppress the most damaging portion of the spike. All MOVs
have response times measured in nanoseconds, while test waveforms usually used to
design and calibrate surge protectors are all based on modelled waveforms of surges
measured in microseconds. As a result, MOV-based protectors have no trouble
producing impressive response-time specifications. Slower-responding technologies
(notably, GDTs) may have difficulty protecting against fast spikes.
5.7.4
Transient surges: These are characterised by different waveforms. The
most frequently referenced IEEE waveform used to simulate lightning induced
transient activity is the combination wave. This wave is characterised by short
duration, high frequency 8/20 µs current and 1.2/50 µs voltage waveform.
5.8
Types of surge protectors:Systems used to reduce or limit high voltage surges can include one or more of the
following types of electronic components. Some surge suppression systems use multiple
technologies, since each method has its strong and weak points. Some of these operate
April 2014
Page 71/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
primarily by diverting unwanted surge energy away from the protected load, through a
protective component connected in a parallel (or shunted) topology. Some others block
unwanted energy by using a protective component connected in series with the power fed
to the protected load, and additionally may shunt the unwanted energy like the earlier
systems.
5.8.1
Metal oxide Varistors (MOV) : A metal oxide varistors consists of a bulk
semiconductor material (typically sintered granular zinc oxide) that can conduct large
currents (effectively short-circuits) when presented with a voltage above its rated
voltage. MOVs typically limit voltages to about 3 to 4 times the normal circuit voltage
by diverting surge current elsewhere than the protected load.
5.8.1.1 MOVs may be connected in parallel to increase current capability and life
expectancy; provided they are matched sets (unmatched MOVs have a tolerance
of approximately ±20% on voltage ratings, which is not sufficient).
5.8.1.2 MOVs have finite life expectancy and "degrade" when exposed to a few
large transients, or multiple smaller transients. As a MOV degrades, its triggering
voltage falls lower and lower. If the MOV is being used to protect a low-power
signal line, the ultimate failure mode typically is a partial or complete short circuit
of the line, terminating normal circuit operation.
5.8.1.3 If used in a power filtering application, eventually the MOV behaves as a
part-time effective short circuit on an AC (or DC) power line, which will cause it
to heat up, starting a process called thermal runaway.
5.8.1.4 As the MOV heats up, it may degrade further, causing a catastrophic
failure that can result in a small explosion or fire, if the line current is not
otherwise limited.
April 2014
Page 72/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.8.1.5 When used in power applications, MOVs usually are thermal fused or
otherwise protected to avoid persistent short circuits and other fire hazards. In a
typical power strip, the visible circuit breaker may be distinct from the internal
thermal fuse, which is not normally visible to the end user.
5.8.1.6 If a surge current is so excessively large as to exceed the MOV parameters
and blow the thermal fuse, then a light found on some protectors would indicate
unacceptable failure.
5.8.1.7 Even adequately-sized MOV protectors will eventually degrade beyond
acceptable limits, with or without a failure light indication.
5.8.1.8 Therefore, all MOV-based protectors intended for long-term use should
have an indicator that the protective components have failed, and this indication
must be checked on a regular basis to insure that protection is still functioning.
5.8.1.9 Because of their good price/performance ratio, MOVs are the most
common protector component in low-cost basic AC power protectors.
5.8.2
Transient voltage suppression (TVS) diode: A TVS diode is a type of
Zener diode, also called an avalanche diode or silicon avalanche diode (SAD), which
can limit voltage spikes.
5.8.2.1
These components provide the fastest limiting action of protective
components (theoretically in picoseconds), but have a relatively low energy
absorbing capability.
5.8.2.2
April 2014
Voltages can be clamped to less than twice the normal operation voltage.
Page 73/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.8.2.3
If current impulses remain within the device ratings, life expectancy is
exceptionally long.
5.8.2.4
If component ratings are exceeded, the diode may fail as a permanent
short circuit; in such cases, protection may remain but normal circuit operation is
terminated in the case of low-power signal lines.
5.8.2.5
Due to their relatively-limited current capacity, TVS diodes are often
restricted to circuits with smaller current spikes.
5.8.2.6
TVS diodes are also used where spikes occur significantly more often than
once a year, since this component will not degrade when used within its ratings.
5.8.2.7
A unique type of TVS diode (trade names Transzorb or Transil) contains
reversed paired series avalanche diodes for bi-polar operation.
5.8.2.8
TVS diodes are often used in high-speed but low power circuits, such as
in data communications. These devices can be paired in series with another diode to
provide low capacitance as required in communication circuits.
5.8.3
Thyristor Surge Protection device (TSPD), a specialized solid-state
electronic device used in crowbar circuits to protect against overvoltage conditions.
5.8.3.1
These Thyristor-family devices can be viewed as having characteristics
much like a spark gap or a GDT, but can operate much faster.
5.8.3.2
They are related to TVS diodes, but can "break over" to a low clamping
voltage analogous to an ionized and conducting spark gap. After triggering, the low
April 2014
Page 74/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
clamping voltage allows large current surges to flow while limiting heat dissipation
in the device.
5.8.4
Gas Discharge Tube (GDT): A gas discharge tube (GDT) is a sealed
glass-enclosed device containing a special gas mixture trapped between two
electrodes, which conduct electric current after becoming ionized by a high voltage
spike.
5.8.4.1
GDTs can conduct more current for their size than other components.
5.8.4.2 Like MOVs, GDTs have a finite life expectancy, and can handle a few
very large transients or a greater number of smaller transients.
5.8.4.3
The typical failure mode occurs when the triggering voltage rises so high
that the device becomes ineffective, although lightning surges can occasionally
cause a dead short.
5.8.4.4 GDTs take a relatively long time to trigger, permitting a higher voltage
spike to pass through before the GDT conducts significant current. It is not
uncommon for a GDT to let through pulses of 500 V or more in duration of 100 ns.
5.8.4.5
In some cases, additional protective components are necessary to prevent
damage to a protected load, caused by high-speed let-through voltage which occurs
before the GDT begins to operate.
5.8.4.6
GDTs create an effective short circuit when triggered, so that if any
electrical energy (spike, signal, or power) is present, the GDT will short this.
April 2014
Page 75/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.8.4.7
Once triggered, a GDT will continue conducting (called follow-on
current), until all electric current sufficiently diminishes, and the gas discharge
quenches.
5.8.4.8 Unlike other shunt protector devices, a GDT once triggered will continue
to conduct at a voltage less than the high voltage that initially ionized the gas; this
behaviour is called negative resistance.
5.8.4.9 Additional auxiliary circuitry may be needed in DC (and some AC)
applications to suppress follow-on current, to prevent it from destroying the GDT
after the initiating spike has dissipated.
5.8.4.10 Some GDTs are designed to deliberately short out to a grounded terminal
when overheated, thereby triggering an external fuse or circuit breaker.
5.8.4.11 Many GDTs are light-sensitive, in that exposure to light lowers their
triggering voltage. Therefore, GDTs should be shielded from light exposure, or
opaque versions that are insensitive to light should be used.
5.8.4.12 Due to their exceptionally low capacitance, GDTs are commonly used on
high frequency lines, such as those used in telecommunications equipment.
5.8.4.13 Because of their high current handling capability, GDTs can also be used
to protect power lines, but the follow-on current problem must be controlled.
5.8.5
Selenium Voltage Suppressor: An "overvoltage clamping" bulk
semiconductor similar to a MOV, though it does not clamp as well.
April 2014
Page 76/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.8.5.1 It usually has a longer life than a MOV. It is used mostly in high-energy
DC circuits, like the exciter field of an alternator.
5.8.5.2
It can dissipate power continuously, and it retains its clamping
characteristics throughout the surge event, if properly sized.
5.8.6
Carbon Block Spark Gap Overvoltage Suppressor: A spark gap is one
of the oldest protective electrical technologies still found in telephone circuits, having
been developed in the nineteenth century. In this type of suppressor, a carbon rod
electrode is held with an insulator at a specific distance from a second electrode. The
gap dimension determines the voltage at which a spark will jump between the two
parts and short to ground. The typical spacing for telephone applications is 0.076 mm
(0.003").
5.8.6.1 Carbon block suppressors are similar to gas arrestors (GDTs) but with the
two electrodes exposed to the air, so their behaviour is affected by the surrounding
atmosphere, especially the humidity.
5.8.6.2 Since their operation produces an open spark, these devices should never
be installed where an explosive atmosphere may develop.
5.8.7
Quarter-wave coaxial surge arrestor : Used in RF signal transmission
paths, this technology features a tuned quarter-wavelength short-circuit stub that
allows it to pass a bandwidth of frequencies, but presents a short to any other signals,
especially down towards DC. The pass bands can be narrowband (about ±5% to ±10%
bandwidth) or wideband (above ±25% to ±50% bandwidth). Quarter-wave coax surge
arrestors have coaxial terminals, compatible with common coax cable connectors
(especially N or 7-16 types).They provide the most rugged available protection for RF
signals above 400 MHz; at these frequencies they can perform much better than the
gas discharge cells typically used in the universal / broad band coax surge arrestors.
April 2014
Page 77/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Quarter-wave arrestors are useful for telecommunications applications, such as Wi-Fi
at 2.4 or 5 GHz but less useful for TV/CATV frequencies. Since a quarter-wave
arrestor shorts out the line for low frequencies, it is not compatible with systems which
send DC power for a LNB up the coaxial downlink. A typical Quarter-wave coaxial
surge arrestor is shown in figure 5.3 below:-
Figure- 5.3
5.8.8 Series Mode (SM) Surge Suppressors: These devices are not rated in Joules
because they operate differently from the earlier suppressors, and they do not depend on
materials that inherently wear out during repeated surges.
5.8.8.1
SM suppressors are primarily used to control transient voltage spikes on
electrical power feeds to protected devices.
5.8.8.2
They are essentially heavy-duty low-pass filters connected so that they
allow 50/60 Hz line voltages through to the load, while blocking and diverting
higher frequencies.
5.8.8.3
This type of suppressor differs from others by using banks of inductors,
capacitors and resistors that shunt voltage spikes to the neutral wire, whereas other
designs shunt to the ground wire. Where ground is bonded to neutral at the electrical
service entrance, the resulting surge ultimately flows into ground at that connection,
but by first dumping into neutral, nearby ground contamination is avoided.
April 2014
Page 78/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.8.8.4
Since the inductor in series with the circuit path slows the current spike,
the peak surge energy is spread out in the time domain and harmlessly diverted into
the capacitor bank.
5.8.8.5 Experimental results show that most surge energies occur at under 100
Joules, so exceeding the SM design parameters is unlikely, but it provides no
contingency should rare events induce energies that exceed it.
5.8.8.6
SM suppressors do present a theoretical fire risk, should the absorbed
energy exceed design limits of the dielectric material of the components.
5.8.8.7
In practice, surge energy is also limited via arc-over to ground during
lightning strikes, leaving a surge remnant that often does not exceed a theoretical
maximum (such as 6000 V at 3000 A with a modelled shape of 8 x 20 µs waveform
specified by IEEE/ANSI C62.41).
5.8.8.8
SM suppression focuses its protective philosophy on a power supply input,
but offers nothing to protect against surges appearing between the input of an SM
device and data lines, such as antenna, telephone or LAN connections, or multiple
such devices cascaded and linked to the primary devices.
5.8.8.9
In this design philosophy, such events are already protected against the
SM device before the power supply.
5.8.8.10 SM low-pass filters are generally not suitable for data communications
circuits, because they would also block high-speed data signals from getting
through.
April 2014
Page 79/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.8.8.11 In comparison to devices relying on components that operate only briefly
and do not normally conduct electricity (such as MOVs or GDTs), SM devices tend
to be bulkier and heavier than those simpler spike shunting components.
5.8.8.12 The initial costs of SM filters are higher, but a long service life can be
expected if they are used properly. In-field installation costs can be higher, since
SM devices are installed in series with the power feed, requiring the feed to be cut
and reconnected.
5.9
Important points regarding installation of Surge Protection at mains input
level and at power distribution boxes:5.9.1
A
comprehensive
surge
protection
system
comprising
of
an
INTEGRATED CLASS B +CLASS C TYPE SURGE PROTECTION SYSTEM is
ideally suited for installation at the mains input and substation switch boards.
5.9.2
The SPD used shall comply with the performance requirements of the IEC
61643 or equivalent.
5.9.3
The Main Surge Protection System is to be installed in the mains input
panel on the LT side. An indicative system is shown in Figure -5.4 below:-
Figure- 5.4
April 2014
Page 80/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.9.4
The system shall offer comprehensive protection against all types of
transient Over Voltages and shall use high capacity MOVs only. It shall be of
combined class B+C type. i.e. it shall be capable of handling Lightning as well as
Switching Surges.
5.9.5
Class B surge protection device (N-G) may consist of encapsulated air gap
device (GDT) and may be used as galvanic separation between N-PE conductors with
following characteristics:i)
Protection mode :
N-PE
ii)
Single pole surge protection device
iii)
Impulse current capacity :
100 kA
iv)
Max current
160 kA
v)
Status indicator available
5.9.6 The surge protection system shall be configured such that the system offers all
mode (Differential) protection. The protection shall be between each phase to neutral,
each phase to earth and between neutral to earth. A typical system is indicated below:-
Figure-5.5
5.9.7
The surge protection system shall comprise of multiple MOV based surge
arrestors housed in an IP 65 enclosure.
April 2014
Page 81/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.9.8
Each Surge arrestor shall consist of at least three elements for backup
protection. Each element of the surge arrestors shall comply with the performance
requirements of the IEC 61643 or equivalent.
5.9.9
The Surge protection system design shall be modular in nature so that the
individual surge arrestors can be replaced after its elements have reached the end of
their life.
5.9.10
The surge arrestors shall be mounted on a DIN RAIL and housed in an IP
65 or equivalent grade enclosure for reliability and ease of replacement / maintenance.
5.9.11
The design shall be such that when a given element fuses, the balance
elements in the surge arrestor continue to offer protection to the installation till it is
replaced with a new one in a short period of time.
5.9.12
When any element fuses, the respective status indicator flag shall turn red
indicating that the element is out of service.
5.9.13
April 2014
Each individual element in the surge arrestor shall be rated as follows : Max. Continuous operating voltage (Uc)
440 V
Min. Lightning impulse current (Iimp)
15 KA ( 10/350 µs) per phase
Nominal discharge current
80 KA(8/20 µs)
Maximum discharge current
150 KA(8/20 µs)
Peak value current
40 KA(10/350 µs)
Specific energy
400 KJ/Ω
Charge
20 As
Protection level
1.9 KV(8/20µs);1.7 KV(10/350µs)
Response time
< 25 ns
Residual current
< 2.5 mA
Follow current
0
Thermo coupler
Present
Fuse
Present
Page 82/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Short circuit withstand
25 KA for 50 Hz supply
Switching surge current (Imax)
100 KA (8/20 µs) per phase
Switching surge current (Inom)
30 KA (8/20 µs) per phase
Clamping voltage
1800 V between L-E, L-N, N-E
Minimum Inom exposures before fusing
20
5.9.14
The surge arrestor elements shall be designed to withstand the specified
Switching Surge Current (Inom) current for a minimum of 20 times without fusing.
5.9.15
The surge protection system shall be connected in parallel with the circuit
and shall not draw the line current. The system shall be connected to the circuit with
10 / 16 Sq mm single core PVC insulated flexible copper conductor cables. The
terminal connectors of the system shall be so designed to avoid any loose connections.
5.9.16
In addition to the Main surge protection Device, which provides combined
Class B & C protection at the main incoming, a series surge filter may be considered
to be installed at all the UPS incoming and outgoing supply which will have the
following features:I)
It shall offer All Mode Protection;
II)
It shall offer redundant protection and staged ;
III)
LED status indication; and
IV)
Option for remote monitoring may be considered.
5.9.17
The surge filter shall filter the surges and transients occurring up to the
branch panels. It shall offer all mode protection for (L-N, L-E and N-E).
5.9.18
It shall conform to ULI 1449 Edition 2 or equivalent for the metallic
enclosure.
5.9.19
The MCB shall be included to ensure safety isolation under power
frequency overload condition.
April 2014
Page 83/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.9.20
It shall be suitable for a line current of 32A or 63A, 3 phase and up to 320
V 50 Hz power supply.
5.9.21
It shall be connected in series. The surge rating shall be 40 kA, 8/20µs.
5.9.22
Each phase surge arrestor employed shall have two redundant and
independent fused and thermal over load protection elements to provide back-up
protection for continued equipment survival.
5.9.23
The technical features shall be as described below:
Normal Voltage
320Vrms(1p), 380V(3p)
Operating Voltage
180-280Vrms(1 ph); 300-480Vrms (3 ph)
Operating Frequency
50 Hz
Connection type
Series
Max. surge rating per line
50 kA to 140kA (8/20µs)
Let through voltage
<380V for 3 KA Cat B
Protection mode
L-N, L-E, N-E
Earth leakage current
< 1 µA
Efficiency
99%
Frequency response
3 dB (at 800 Hz)
Response time
< 5 ns
Standards compliance
BS6651-1999 cat.A.B.C
AS1768-2003 cat.A.B.C
IEEE C62.41 cat.A.B.C
CP33-1999 cat.A.B.C
IEC 1000-4 5 1995
UL 1449 second edition
April 2014
EMC Compliance
BS EN 60950 : 1992; BS EN 61000 : 1999
Alarm isolation
4 Kv
Status indicator
LED
Optional remote alarms
Siren sound OK and FAIL LED
Alarm(volt free contact)
N/O, N/C(2A@250Vac)
Alarm conductor size
2.5mm²
Conductor size
35 mm²
Mounting
Back panel screw mount
Page 84/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.10
Enclosure material
Galvanized steel alloy
Enclosure IP rating
IP 55
Operating temperature
- 40 -85ºc
Humidity
0-95% (R.H)
COMPUTER NETWORK PROTECTOR: -
The Cat5, Cat 5e, Cat 6 and POE (Power over Ethernet) cables shall be provided with a
suitable surge protector. It shall be suitable for RJ 45 connectors
5.10.1
It shall be designed to protect all widely used computer network system
using Ethernet twisted pairs technology like 10/100/1000 Base T, CDDI, ATM155
and also the Power-over-Ethernet.
5.10.2
It shall offer protection against transient over voltages due to lightning
induced surges, AC power interference and ground loop energies appearing between
any signal pair and / or its ground which can damage the sensitive network
equipment.
5.10.3
The series protector shall be designed to protect both common and
differential mode in all the 8 pins of the RJ 45 port and its ground lead.
5.10.4
It shall have the latest circuitry using Silicon Avalanche diode to ensure
very fast response time and exceptional low let-through voltage which results in
maximum system reliability and up-time.
5.10.5
The shunt capacitance shall be 5pf and negligible in-line resistance so that
even the most demanding high speed gigabit multimedia signal can be passed without
much signal degradation.
5.10.6
It shall be compact, in-line and simple plug-in design to enable it to be
easily located near the protected equipment.
April 2014
Page 85/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.10.7
5.11
The technical features shall be as described below:-
Max. working Voltage
5V
Max. operating current
300mA
Protection modes
Common and transverse
Lines protected
All pairs
Response time
Max. surge rating
< 5 ns
100A (8/20µs)
Max. Data rate
Let through voltage
100Mb/s (C5, PoE models), 1000Mb/s(C6 models)
23V (A1 5 KV 10/700µs)
Shunt capacitance
In line resistance
5pF (single port models), 25pF(rack-mount models)
-0 Ω
Standards compliance
100 Base T , 1000Base T, CAT5, CAT5e , CAT6
Connector type
RJ 45
Earth connection
Flying lead(single port models)
Enclosure material
Earth stud(rack-mount models)
Anodized aluminum (single port)
Operating temperature
Galvanized steel alloy(multi-port)
- 40 ºc to 85 ºc
Humidity
0-95% (R.H)
Altitude
0-3650m
Telecom line protector: All the telecommunication lines shall be protected with a
suitable Surge Protector to protect the modems and other sensitive equipment’s. It shall
be designed to protect all widely used telecommunication lines like PSTN, ISDN, DDN
and DSL using twisted pairs. Different connectors like RJ45, RJ11 and plug/socket
models shall be used to obtain optimum protection.
Following are the main characteristics of Telecom line protector:5.11.1
The hazard of lightning induction in telephone lines can be managed by
using transient protection units in parallel with each line. These multi line protection
can have multi stage protection i.e. Hybrid GDT for over voltage protection and PTC
for over current protection.
April 2014
Page 86/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.11.2
It shall offer Protection against Transient over voltages due to lightning
induced surges, AC power interference and ground loop energies appearing between
any signal pair and/or its ground that can damage the sensitive telecommunication
equipment.
5.11.3
The protector shall be designed to protect both common and differential
mode in all the connected pins of the RJ 45 or RJ 11 port and its ground lead.
5.11.4
They shall be multi-stage design which employ a combination of high
energy gas discharge tube, ultra fast diodes and SAD which results in maximum
system reliability and up-time.
5.11.5
It shall have 20KA surge handling capability and 20MHz high bandwidth,
so that it can provide the safest protection in lightning intense environment to ensures
a smooth data traffic.
5.11.6
It shall be compact, in-line and simple plug-in design enabling it to be
easily located near to the protected equipment.
5.11.7
The important technical features of Telecom Line Protector are described
as below:-
Max. working Voltage
190v (PSTN) , 60 V (ISDN) ,68 V (DDN)
(Line to line)
50 V (XDSL)
Max. operating current
150mA
Protection modes
Common and transverse
Lines protected
2 wires (RJ11-pin3&4, RJ45-pin4&5)
4 wires(RJ11-pin 3&4, 2&5, RJ 45-pin 4&5, 3&6)
Response time
< 5 ns
Max. surge rating
20A (8/20µs)
Max. Data rate
20Mb/s
April 2014
Page 87/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Let through voltage
220V (PSTN) , 80 V (ISDN)
(at 5KV 10/700µs)
78V (DDN) , 60V (xDSL)
Shunt capacitance
< 150pF
In line resistance
3.9 Ω
Standards compliance
BS6651-1999, AS1768-2003
IEC61643-21 , ITU(CCITT)1X K17
Connector type
RJ 45 or RJ 11
Earth connection
Flying lead (single port models)
Earth stud (rack-mount models)
Enclosure material
Anodized aluminum (single port)
Galvanized steel alloy (multi-port)
5.12
Operating temperature
- 40 ºc to 85 ºc
Humidity
0-95% (R.H)
Altitude
0-3650m
DATA PORT PROTECTOR: -
The SPD for Data Line shall be based on transistor and diode circuitry which ensures a
lower let through voltage to protect from the surge and transient overvoltage. Following
are the main characteristics of Data Port Protector:5.12.1
In case of the Surge current above the Rated capacity it shall fuse and
isolate the sensitive equipment.
5.12.2
It shall offer common mode & Transverse mode protection against the
Transients appearing between any signal pairs.
5.12.3
The DPP RS232 port protectors shall be compact and in-line design which
can be easily connected to the data of the equipments.
5.12.4
The V.35 and the RJ21X data port protectors shall be easily secured onto a
standard 35mm Top Hat DIN rail.
April 2014
Page 88/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.12.5
It shall have fast response circuit not only to protect the equipments from
repeated surges but also to allow the DPP protectors to transparently transmit the data
at a speed of up to 20 Mbps.
5.12.6
DPP protector shall offer nearly zero in line resistance and a 40pF
capacitance which allows the data to transmit smoothly on the lines.
5.12.7
The important technical features of Data Port Protector are described as
below:Max. operating current
300mA
Protection modes
Common and transverse
Response time
1 ns
Max .surge rating
200A (8/20µs)
Max. Data rate
20Mb/s
Insertion loss
<1dB at 20 MHz
Capacitance
40pf
Standards compliance
BS6651-1999 Cat.A.B.C
AS1768-2003 Cat A.B.C
Connector type
IEC61643-21, ITU(CCITT)1X K17
DB9 female to male (DPP9)
CP33-1996 Cat A.B.C, UL497B
DB25 female to male(DPP25)
Enclosure material
M/34 female to male(DPP35)
DIN clip (DPP35, DPP50)
RJ21X female to male (DPP50)
Flying lead(DPP9),shell(DPP25)
Anodized aluminum (DPP35, DPP50)
Operating temperature
Plastic (DPP9, DPP25)
- 40 ºc to 85 ºc
Humidity
0 to 95% (R.H)
Altitude
0-3650m
Earth connection
April 2014
Page 89/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.13
RF COAXIAL PROTECTOR:-
RF Coaxial protectors are intended to pass through a desired RF signal with minimum
loss or disturbance. To minimize the impact of inserting lightning protectors within the
RF circuit, seek out products with the lowest Insertion Loss and lowest VSWR at the
frequencies that is intended to operate.
5.13.1 Other important main characteristics of RF Coaxial Protector (Fig 5.6) are:i)
Reliable RF performance capability from DC – 3GHz
ii)
Multi – strike capability
iii)
Easily replaceable gas discharge tube
iv)
Bi-directional protection
v)
AC/DC pass
vi)
High quality construction
vii)
Full range of connector type
Figure-5.6
5.13.2 The coaxial RF protectors shall be a high performance gas discharge tube
suppressor capable of wide-band operation from DC up to 3 GHz (N, SMA and D type
connector).
5.13.3
The let-through voltage shall be as low as possible and it is capable of
handling multi-strike in any lightning intensive environment.
April 2014
Page 90/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.13.4
CGR protectors feature easily replaceable gas tube arrester elements,
which makes it simple, fast and cost effective in case replacement of the gas tube is
required.
5.13.5
Both connector ports of this protector shall be equally protected. This
provides protection no matter which way it is installed.
5.13.6
The important technical features of RF Coaxial Protector are described as
below:-
Frequency range
0-3GHz
VSWR
< 1.1:1
Return loss
> 26dB
Insertion loss
< 0.2dB
Impedance
50 Ω for all models
Response time
<5ns
Peak surge rating
20 kA (8/20µs)
DC spark over voltage 90V+/- 20%
(230,350,600,1000V)
Max .power
0 – 2000 W
Standards compliance
ITU(CCITT)1x K17
BS6651-1999 Cat.A.B.C
AS1768-2003 Cat A.B.C
CP33-1996 Cat A.B.C
IEC61643-21/UL497B
April 2014
Body material
Brass(Nickel plated)
Contact pin
Brass(silver/gold plated)
Contact socket
Beryllium or tin brass(silver/gold plated)
Elastic contact
Beryllium or tin brass(silver/gold plated)
Insulator
PTFE
O-ring material
Silastic
Earth connection
Via suitable screw ground lug
Page 91/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Mounting
L shape bracket
Operating temperature -4-85ºc
5.14
Humidity
0-95% (R.H)
Altitude
0-3650m
IP rating
IP 65
Moisture resistance
MIL-STD-202 Method 106D
Salt fog
MIL-STD-202 101D/B
Temperature shock
MIL-STD-202 107D/A-1
Vibration
MIL-STD-202 Method204D/B
Telephone Line Protector (Krone Type)
The main characteristics of Telephone Line Protector
which provides surge
protection for telecom and other signalling equipment’s terminated on KRONE
connectors are:5.14.1
The protector shall be available in various assorted configuration like 1
pair, 10 pair, 50 pair etc in a compact module having multi stage protection.
5.14.2
Full range of voltage to suit any particular applications and the let-through
voltage shall be as low as possible.
5.14.3
The series protectors shall be easily pluggable type into the KRONE LSA-
PLUS disconnection blocks and shall be earthed suitably.
5.14.4
It shall offer both line to line (transverse mode) and line to earth (common
mode) protection.
5.14.5
It shall have 20 KA high surge rating and 20 MHz wide bandwidth to
provide the best protection and to ensure a smooth data flow in high speed data and
signal lines.
April 2014
Page 92/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.14.6
It shall be designed in such a way that the surge exceeding the capacity of
the primary gas arrester, service should be interrupted by blowing the track fuse and
thereby giving a fault condition.
5.14.7
The important technical features of Telephone Line Protector are described
as below:Max. working voltage
7-280V
Max. operating current
250Ma
Protection modes
Common and transverse
Protection stages
3 stages
Earth leakage current
< 5 µA
Response time
<5ns
Max. surge rating
20 kA (8/20µs)- KDP 10
5 KA (8/20µs) – KDP 1
Max. data rate
20 Mb/s
Insertion loss
< 1dB at 20 MHz
Let through voltage:
10-320 V
(At 5KV 10/700 µs)
Capacitance
50 pf
In line resistance
3.9Ω
Standards compliance
ITU(CCITT)1x K17
BS6651-1999 Cat.A.B.C
AS1768-2003 Cat A.B.C
CP33-1996 Cat A.B.C
IEC61643-21
UL497B
Earth connection
Via earth clips on two ends – KDP 10
Via earth bar – KDP 1
April 2014
Enclosure material
ABS plastic
Operating temperature
- 40 ºc to 85 ºc
Humidity
0-95% (R.H)
Altitude
0-3650m
Page 93/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.15
Installation notes and Important points in context of installation of
Lightning, Surge Protection and Earthing Systems:5.15.1
A Connection made up by materials which do not comply with the
chemical chain of materials choice like Copper and steel irrespective of their grade is
not allowed to be connected with unless separated by appropriate means as stipulated
within IEC-62305-3.
5.15.2
IEC stipulates that the spark gaps used for single or multiple load be 100
kA at 8/20 µs single rated. Anything above 60 V is deadly for human life.
5.15.3
IEC 62305 regulatory norm permits only one common grounding network.
This common grounding network must interconnect or cross mesh all the sub
components of the LLZ system like its building, LLZ antenna array, and NF Monitor.
Even the grounds of lightning protection system needs to be connected to the common
grounding network. All external metal structures must be connected to the ground
network. If there is any other equipment installed at the LLZ site, the same must
necessarily be given relevant lightning protection not only for the sake of the
equipment itself but for the sake of the whole LLZ installation.
5.15.4
Implement lightning protection system compliant to IEC 62305 of Cat I.
This does not permit the use of such ionizing devices like the prevectron which
promise prevention of lightning and wider coverage.
5.15.5
Lightning protection by systems like “Early Streamer emission”,
“Dissipation Array Systems” or “Charge Transfer Systems” are not allowed under
standards of US National Fire Protection Association (NFPA), IEC, IEEE,
Underwriters Laboratories (UL), US Military etc.
5.15.6
April 2014
The power cable shielding must be connected to a common ground point.
Page 94/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.15.7
The mains in-leading and out-leading armoured power cable must have its
shield grounded with its PEN conductor to one common ground bus bar. The
grounding must be done within 20 cm of the cable entry/exit point to/from the
building.
5.15.8
The mechanical shield of each RF cable entering or leaving the building
must be bonded to the ground at the point where it enters/leaves the building, but not
more than 20 cm inside the building. Preferably it should be done outside the
building.
5.15.9
The COM cable used for data communication should have its mechanical
armouring and inner static shield connected to ground only at one end, say the TWR
side and not at both ends. Connecting to ground at both ends is likely to induce strong
equalizing ground current between different potentials of such far away buildings,
which may reach values above 100 A under worst condition. The other end, both the
armour as well as the shield should be grounded through a spark gap to the nearest
common ground. The spark gap should be IEC 62305 compliant with low spark over
voltage level (< 70 V AC) and high current rating values of 75 kA at 8/320 µs or
more.
5.15.10
The IEC 62305 stipulates that there is only one common ground
connecting all potentials to one, as well as the PEN, the power cable shield, the COM
cable shield, any internal PE and grounds of SPDs, any RF cable shields and others
like external groundings and lightning protection inclusive of the subsystems e.g. LLZ
antenna, NFM etc.
5.15.11
RF cables entering the shelter must have in line surge arrestors.
5.15.12
The PE wire/conductor of a power cable is not a ground connection. The
ground connection for static issues must use a connecting wire of cross sectional area
16 mm2 or more and use the shortest path to the near most ground.
April 2014
Page 95/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.15.13
All multi strand wire must use cable end sleeves and cable end lugs to
enable proper installation and also to reduce chemical chain involved in corrosion.
Any flat tape or round wire / cable connections must utilise termination clamps or
brackets.
5.15.14
The cable routing of various voltage circuit must be separated, for e.g. the
RF, the AC, the DC and the GND and static shields of all the cables must be grounded
at point of entry into the building.
5.15.15
All shielded cable like RF, COM, armoured PWR line etc. should be
connected to common potential ground at every 20 m along its external path. Same is
to be done at every 2.5 m when internally laid.
5.15.16
Common ground network for a DVOR must be connected, DVOR
building, Counterpoise steel structure, Counterpoise mesh, power cable shielding,
power cable PEN wire, COM cable shield via spark gap, ground connection to SPD
related to PWR, COM or RF cabling, Lightning protector rods, DVOR monitor
mast/antenna, and other metallic objects of the system.
5.15.17
Copper can be bonded to galvanized steel via special bimetal media or
stainless steel media of V4A grade.
5.15.18
PE: Protective earth; PEN: Combined protective earth and neutral; N :
Neutral must all be connected to a common bus bar. Electrical conductors entering a
structure should be metal cased. This metal casing should be electrically continuous
within the structure; it should be earthed at the point of entry inside the structure on
the user’s side of the service and bonded directly to the lightning protective system.
April 2014
Page 96/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.15.19
Where the electrical conductors are connected to an overhead electricity
supply line, a 15 m length of buried armoured cable should be inserted between the
overhead line and the point of entry to the structure.
5.15.20
The overhead supply lines are liable to have large surges induced in them
from lightning discharges. Hence is, therefore, needed where they join the buried
cable. This will allow a large part of the lightning current to be discharged to earth at
a safe distance, which is determined by the rolling sphere’s radius, from the
structure.
5.15.21
Surge suppressors should be installed with minimum lead lengths to their
respective panels. Under fast rise time conditions, cable inductance becomes
important and high transient voltages can be developed across long leads.
5.15.22
In all instances, use high quality, high speed self diagnosing protective
components.
5.15.23
Proper ground must be ensured. Earth resistance to be strived to achieved
to be as low as possible preferably less than 5 Ω.
5.15.24
Do not install suppressor, if neutral to ground bond is not present.
5.15.25
If neutral to ground voltage is greater than 2 V AC, the electrical system is
faulty and needs to be rectified.
----------------------------------------
April 2014
Page 97/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter - 6
Measurement of Earth Resistance
6.1
Measurement of Earth Resistivity:-
6.1.1
Need for the measurement of Resistivity:-
The resistivity of the soil varies within extremely wide limits, between 1 and
10,000 Ω-meters. The resistivity of the soil is found to be non-uniform at many station
sites. To design the most economical and technically sound grounding system for large
installations, it is necessary to obtain accurate data on soil resistivity and on its
variation. Resistivity measurements at the site help in designing a good earthing
system. The resistivity of the earth varies over a wide range depending on its moisture
content. It is therefore, advisable to conduct earth resistivity tests during the dry season
in order to get conservative results.
6.1.2
Test Locations:-
In the evaluation of the earth resistivity of, at least eight test directions should be
chosen from the centre to cover the whole site. This number shall be increased for very
large station sites and for sites where, the test results obtained at various locations
show a significant difference, indicating variations in soil formation.
In case of transmission lines, the measurements shall be taken along the direction
of the line throughout the length approximately once in every 4 kilometers.
6.2
Principle of Tests:6.2.1
Wenner’s four electrode method is recommended for these types of field
investigations. In this method, four electrodes are driven into the earth along a
straight line at equal intervals. A current I is passed through the two outer electrodes
and the earth as shown in figure below and the voltage difference V observed
between the two inner electrodes. The current I flowing into the earth produces an
electric field proportional to its density and to the resistivity of the soil. The voltage
April 2014
Page 98/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
V measured between the inner electrodes is, therefore, proportional to the field.
Consequently, the resistivity will be proportional to the ratio of the voltage to current.
If the depth of burial of the electrodes in the ground is negligible compared to the
spacing between the electrodes, then:ρ = 2π SV / I
Earth testers normally used for these tests comprise the current source and meter in a
single instrument and directly read the resistance. The most frequently used earth tester
is the four –terminal Megger shown in Fig 1. When using such a Megger, the
resistivity may be evaluated from the modified equation as given below.
ρ = 2π x SR
Where
ρ = resistivity in ohm – meters
S = distance between successive electrode in meters
R = Megger reading in ohms.
C1, C2
Current Electrodes
P1, P2
Potential Electrodes
Fig. 6.1 Measurement of Earth Resistivity
----------------------------------
April 2014
Page 99/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter -7
Supply, Installation, Testing and Commissioning [SITC] of Lightning, Surge
Protection and Earthing System of CNS Facilities as part of Turnkey Project.
7.1 When Lightning, Surge Protection and Earthing System of CNS Facilities are being
procured under SITC as a part of turnkey project, General Technical specifications of the
Tender Document in such cases should clearly specify following:
The vendor/supplier/system integrator shall be responsible for complete Supply,
Installation, Testing and Commissioning of the Lightning, Surge Protection and
Earthing System of the facility.

The vendor/supplier/system integrator shall design and provide a comprehensive
Lightning, Surge Protection and Earthing System which shall meet the following
National and International Standards:IS-2309
Code of protection for Lightning Protection
IS -3043
Code of practice for earthing
IS -5216
Safety procedures & practice in electrical work
IEC -62305
Protection against Lightning
IEC -61643
Low Voltage Surge Protective Devices
IEC -60364
Low Voltage electric Installation:
ANSI/UL 467
Grounding & Bonding Equipment
7.2 The lightning & Surge Protection System provided shall be a comprehensive system
i.e. it should include:7.2.1 Power Supply Surge Protection System at the input of Equipment room where
the facility is proposed to be installed and each distribution board which will supply
power to the equipment and its accessories.
7.2.2 Surge Protection system should be provided to all incoming and outgoing cables
connected to system such as Data lines [Telephone, OFC, RC cables etc] and RF
Cables etc. Standard bonding of cable shields/trays to ground at building entry/exit
points must be ensured.
7.2.3 Air Terminals/Lightning Rods should be positioned to give full coverage of
structure [Building, Antenna, Mast etc.] against the lightning.
April 2014
Page 100/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
7.2.4 Earthing system shall meet the following requirements:
7.2.4.1 Provide safety to equipment from power line faults, lightning and surges.
7.2.4.2 Provide a common reference ground plane for electronic equipment which
will minimize electronic system noise and electromagnetic interference (EMI).
7.2.4.3 The grounding system design shall be based on single grounding network
with multiple earths.
7.2.5 Appropriate references should be made to the guidelines provided in the manual
in this regard.
7.2.6 If only a part of Lightning, Surge Protection and Earthing System e.g. only surge
protection system is to be supplied by vendor then also appropriate references should
be made to standards in this regard in the tender document.
7.3 Any other specific requirement for Lightning, Surge protection and earthing system
specific to the equipment being procured should also be clearly specified in the Tender
Document.
7.4 Lightning, Surge Protection and Earthing System of CNS facility shall form a part of
Factory Acceptance Test (FAT) and Site Acceptance Test (SAT).
7.5 The complete layout of the Lightning, Surge Protection and Earthing System of CNS
facility shall be submitted by the vendor/supplier/system integrator before
commissioning.
----------------------------------
April 2014
Page 101/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter -8
Maintenance Procedures of Lightning, Surge Protection and
Earthing Systems
8.1Responsibility of Maintenance
Maintenance of Earthing, Lightning and Surge Protection System for the CNS
installations installed in Terminal Building and/or Technical Block and located inside
operational area and around airport (Radar, LLZ, GP, DVOR, OM/MM and NDB etc. )
shall be looked after by the CNS personnel.
8.2 Testing :8.2.1 On the completion of the installation, or any modification to it, the following
measurements should be made and the results recorded in a lightning protective
system log book:
i)The resistance to earth of the whole installation and of each earth termination.
ii)
8.2.2
The electrical continuity of all conductors, bonds and joints.
If the resistance to earth of a lightning protective system exceeds 5Ω, the
value should be reduced. If the resistance is less than 5Ω, but significantly higher than
the previous reading, the cause should be investigated and any necessary remedial
action should be taken.
8.2.3
Tests should be repeated at fixed intervals, preferably not exceeding 06
months.
8.2.4
It is emphasized that before isolating a lighting protection earth, it should
be tested to ensure that it is not “live”, using a sensitive voltage device.
April 2014
Page 102/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
8.3
System Inspection:-
8.3.1
All lightning protective systems should be visually inspected by a
competent person during installation, after completion and after alteration or
extension, in order to verify that they are in accordance with the recommendations in
this code.
8.3.2
Visual inspections should be repeated at fixed intervals, preferably not
exceeding 03 months.
8.3.3
In addition, the mechanical condition of all conductors, bonds, joints, and
earth electrodes (including reference electrodes) should be checked and the
observations noted.
8.3.4
If, for any reason, such as other site works, it is temporarily not possible
to inspect certain parts of the installation, this also should be noted.
8.4
Total System Maintenance
8.4.1
Of particular importance is the regular detailed examination of the
complete LPS for any evidence of corrosion. If this check is not carried out then vital
components within the LPS, which may have suffered from corrosion and which
could exhibit a high resistance could be missed. This will have a detrimental effect
on the whole system making it an unattractive high impedance path for the lightning
current to follow.
8.4.2
The earth resistance for all the electrodes must be measured periodically
to ensure their usability.
8.4.3
The resistance of the air terminals to the earth electrode should also be
measured periodically.
April 2014
Page 103/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
8.4.4
Maintenance Checks For Lightning Protection System
Following checks should be carried out at regular interval – once every 06 months:
8.4.4.1 Inspection of Air Terminal
Physical inspection of air terminal and functionality checks with air terminal test
meter.
8.4.4.2 Inspection of Down-conductors
 Check for corrosion
 Continuity testing by continuity tester, across all types of conductors in
lightning protection and grounding system. The resistance should be strived
to be as less as possible preferably less than 5.0 ohm.
 The down conductors are routed, located and electrically bonded as
required.
8.4.5 Periodic Check for Earthing System:
 Earth resistance will be checked at the interval of 6 months with the standard
process of measurement (Three point method) and recorded. If the measured value is
beyond specified standards, corrective action must be taken.
 Earth termination systems are interconnected. Where a conductor is totally hidden,
its electrical continuity should be tested.
 In case specified standards of earth resistance are not met, ground conductivity
may be improved by
 Refilling of earth pit with electrolytic compound for electrolytic grounding system
where provided.
 Recharging of earth pits in case conventional grounding system is installed.
 Physical inspection of connection between ground rod and down conductor near
grounding system for corrosion, bad contacts followed by corrective action.
April 2014
Page 104/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
8.4.6 Inspection of Surge Protection devices:
 All surge protection devices should be checked at an interval of 3 months for their
functionality.
 Indications provided with surge protection system should be monitored and
recorded on daily basis.
 Faulty devices should be replaced.
8.4.7 Earthing System Inspection Chambers
Inspection Chambers of each earthing system should be maintained properly.
Grass and other wild growth should be regularly cleared around inspection chamber.
Whenever grading or other civil works takes around these chambers, they should be
protected properly and should not be allowed to be lost during such works.
8.5
Special Total System Inspection:
In the event of occurrence of major lightning strike around the Terminal building
and other CNS facility as observed or monitored on the strike record counter, all the
aforesaid inspection should be carried out and if need be, the corrective measures to be
taken immediately so that LPS is maintained in its optimal effectiveness.
8.6
Inspection Regarding Modifications / Repairs of the Protected Structures
While carrying out the periodic maintenance particular attention should be paid,
besides earthing and corrosion, to alteration or extensions to the structure that may affect
the LPS. Examples of such alterations or extensions are:a) Change in the use of building;
b) Installation of fuel oil storage tank near to building;
c) Erection of radio aerials; and
d) Installation or alteration to electrical, telecommunications or computing
Facilities within or closely connected to the building.
April 2014
Page 105/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
8.7 Records
The following records should be kept on site, or by the person responsible for the
upkeep of the installation:a)
Scale drawings showing the nature, dimensions and position of all
components and Parts of the LPS.
b)
The nature of the soil and any special earthing arrangements.
c)
Date and particulars of salting, if used.
d)
Test conditions, date and results.
e)
Alterations, additions or repairs to the system.
f)
The name and contact details of the person/s responsible for the
installation or
its upkeep.
------------------------------------------------
April 2014
Page 106/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
Chapter -9
DEFINITIONS and ACRONYMS
9.1 DEFINITIONS
In this Manual, the following definitions shall apply.9.1.1
Lightning Flash
: Electrical discharge of atmospheric origin between
cloud and earth comprising one or more impulse of many kilo amps
9.1.2
Lightning Strokes
: The single distinguishable current impulse of a
flash.
9.1.3
Lightning Protective System: The whole system of conductors used to
protect a structure from the effects of lightning.
9.1.4
Air Termination (Air Termination Network) : That part of a lightning
protective system which is intended to intercept lightning discharges.
9.1.5
Down Conductor: Conductor that connects an air termination with an
earth termination.
9.1.6
Bond: A conductor intended to provide electrical connection between the
lightning protective system and other metalwork and between various portions of the
latter.
9.1.7
Joint: A mechanical and/or electrical junction between two or more
portions of a lightning protective system.
9.1.8
Testing Joint: Joints designed and situated so as to enable resistance or
continuity measurements to be made.
9.1.9
Earth Termination (Earth Termination Network) : That part of a
lightning protective system which is intended to discharge lightning currents into the
general mass of the earth. All points below the lowest testing point in a down
conductor are included in this term.
9.1.10
Earth Electrode: That part of the earth termination making direct
electrical contact with earth.
April 2014
Page 107/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
9.1.11
Ring Conductor: Earth termination or electrode fixed to a structure above
or below the earth or within or under foundations. A ring conductor may be used alone
as an earth termination network or in conjunction with metal rods as an
interconnection conductor.
9.1.12
Indicating Plate:
A plate detailing the number and position of earth
electrodes.
9.1.13
Reference Earth Electrode:
An earth electrode capable of being
completely isolated from an earth termination network for use in periodic testing.
9.1.14
Log Book:
A record of tests and inspections of a lightning conductor
installation.
9.2 Acronyms
A
: Ampere
ASR
: Airport Surveillance Radar
ARSR
: Air route Surveillance Radar
ANSI
: American National Standard Institute
ATM system
: Air Traffic Management System
BS
: British standards
BIS
: Bureau of Indian Standards
cm
: centimeter
CNS
: Communication Navigation Surveillance
CNS-OM
: CNS –Operation & Maintenance
Deg.
: Degree
dia
: Diameter
DME
: Distance Measuring Equipment
ES
: Earthing System
EES
: Earth Electrode System
IS
: Indian Standards (Bureau of India Standards)
IEC
: International Electro technical Commission
IEEE
: Institute of Electrical and Electronics Engineers
April 2014
Page 108/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
LA
: Lightning Arrestor
LLZ
: Localizer
LPS
: Lightning Protection System
Ft
: Feet
GP
: Glide Path
kA
: Kilo Ampere
kmph
: Kilometer per hour
kV
: Kilo volt
M(m)
: Meter
mm
: millimeter
ms
: mill second
MIL –STD
: Military Standard
EEB
: Equi-potential Earth Bus bar
MEEB
: Main Equi-potential Earth Bus bar
NDB
: Non Direction Beacon
NF
: Near Field
NFPA
: National Fire Protection Association
MV
: Mega Volt
RF
: Radio Frequency
SMR
: Surface Movement Radar
UL
: Underwriters Lab.
V
: Volt
VLSI
: Very Large Scale Integrated Circuit
----------------------------
April 2014
Page 109/110
Version 2.0
Airports Authority of India
CNS Manual Vol. V
Lightning, Surge Protection and Earthing
System for CNS Installations
------------------------------------------------------------------------------------------------------------------------------------------------------------------
******End of CNS Vol. V Ver. 2.0 *****
April 2014
Page 110/110
Version 2.0