1. UMTSRNS_108 Earthing and Lightning
Protection
Purposes:
 Understand Earthing Theory
 Understand Lightning Protection Theory

3. i
Contents
Chapter1 Earthing Theory............................................................................................................ 1
1.1 Summary............................................................................................................................. 1
1.2 Terms ................................................................................................................................. 1
1.3 Earthing Basic Requirement .................................................................................................. 5
1.3.1 Common Earthing........................................................................................................ 5
1.3.2 Power Supply System................................................................................................... 8
1.3.3 Equal Potential Connection ..........................................................................................10
1.3.4 Device Protection Ground Cable...................................................................................11
1.3.5 Cabling Requirement ..................................................................................................13
Chapter 2 Lightning Protection Theory ........................................................................................15
2.1 Lightning Protection Concept ...............................................................................................15
2.2 Different Level of Lightning Protection Measures ...................................................................17
2.2.1 First Level Lightning Protection ...................................................................................17
2.2.2 Third Level Lightning Protection..................................................................................18
2.2.3 Second Level Lightning Protection ...............................................................................18

5. 1
Chapter1 Earthing Theory
 Key Points
 Purpose and Types and Modes of Earthing
 Earthing Terms
 Basic Earthing Requirements
1.1 Summary
The main purposes of earthing for communication systems are:
● Interference Prevention
● Static Electricity Prevention
● Overvoltage Prevention
Types of earthing for communication systems are classified into:
● DC power earthing
● Protective earthing
● Lightning protection earthing
Earthing modes of mobile communication systems are classified into:
● Common bonding network
1.2 Terms
● Earth
Earth in earthing systems is commonly referred to the ground. It has electric
characteristic and serves as a return path for electric current and is used as
reference electrode.
● Bonding Conductor
This is the conductor that connects the communication devices and the bonding
bar.

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● Ground Connection Conductor
This is the conductor used toconnect lightning protection device of the building
and every bonding bar to the ground grid. Among them, the conductor used to
connect each bonding bar to the ground grid is called ground connection
conductor.
● Bonding Bar
This is the metal component used to connect the bonding conductor (which is
commonly called ground copper plate), which can be classified into head
bonding bar and branch bonding bar. Branch bonding bar includes horizontal
branch bonding bar, vertical branch bonding bar and receive-line branch
bonding bar and so on.
● Equal Potential Bonding
This is the bonding conductor between two devices and should be connected
with thin wires as short as possible. It controls the instant electric potential
difference between two devices within design range when boding conductor is
discharging the maximum possible electric current. This kind of bonding is
called equal potential bonding, as shown in Figure 1-1.
等电位连接线
设备
A
设备
B
设备
C
Equal Potential Cable
Device Device Device
Equal Potential Bonding
Fig.1-1 Equal Potential Bonding of Multiple Cabinets
Typical equal potential bonding has: wire length less than 0.5m, wire diameter
more than 6mm2
, and several lines of copper wires with joint. In whorl
installation, if whorl diameter is more than 12mm, please use wire nose or
copper mat to compact and use one screw for one wire only.

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● Earth Potential Rise
Because devices are placed in different joints and end points of earthing grid,
when they discharge the lightning electric current, different part of bonding bar
has different potential rise, different devices have different electric potential
difference to earth in a short period of time. It is called earth potential back
strike or earth potential rise.
● External Lightning Protection System
This is the part in lightning rod, strap, grid and aerial lightning cable that
receives the lightning directly. This also includes the metal room surface and
metal component and such things that are used for lightning protection.
● Earthing and Bonding System
This is the collection of ground grid, earthing connection cable, bonding bar
and bonding conductor, as shown in Figure 1-2.
接地引入线
接地汇集线
连接扁钢
接地引入线
电力室（一层）
机房（二层）
地网
Earthing Bonding Cable
Equipment Room
(2nd Floor)
Flat Steel Bar
Electric Power Room
(1st Floor)
Ground Grid
Earthing Connection
Earthing Connection
Fig.1-2 Earthing and Bonding System
Earth has electric characters and unlimited electric capacity. It is a good
common earthing reference electric potential. Earthing electrode is the metal

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endpoint or equivalent that connects earth electrically to discharge electric
current to earth. Earthing connection is the part that connects earthing electrode
to indoor (or outdoor) bonding bar. Bonding bar is indoor (or outdoor) bonding
copper bar used to concentrate bonding conductors. Bonding conductor is the
cable that connects device to bonding bar.
● DC Power Ground
This is the circuit component which has DC 0V relative to earth and part of the
DC power structure. DC power earth normally connects to earth via bonding
bar.
● Protective Ground
This is the shell of the device and its bonding conductor that connects to
bonding bar and protective bonding conductor in the three-phase five-wire
standardAC power systems.
● Lightning Protection Ground
This is the bonding conductor that connects various kind of lightning protection
devices installed in the building for direct strike lightning protection to the
ground grid.
● Common Bonding Grid
This is the earthing mode in which DC power ground and protective ground of
all devices in communication site (station) and lightning protection ground of
the buildings share same underground ground grid.
● Surge Protection Device
This is the device to protect communication systems from various kind of
lightning electric current, operative overvoltage and so on in the
communication site (station).
● Central Office Communication Building
Central office communication building includes communication buildings such
as international communication site, switch site, local switch site with more
than 10,000 lines, long distance call site with more than 2000 lines and mobile
switch site.

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● End Office Communication Building
This is the communication building that is not central office communication
building, for example, local end office site only with simple protection or inside
the buildings of shopping center, offices, rooms and streets, which have no
protection at all.
End office communication building includes small communication site such as
end office building of access network at remote site, mobile base station, and
access module of switch.
● Outdoor Communication Devices
Outdoor communication devices, such as base station on top of building or
tower, repeater, tower amplifier, outdoor lightning protection device, and
remote radio device.
● Nominal Discharge Current
This is the 8/20μs waveform peak current going through SPD, and it is used
in class I test for SPD classification, class I and II SPD preprocessing test.
Please refer to standard YD1235 for test class definition.
● Maximum Discharge Current
This is the maximum endurable discharge current in dynamic load test which is
a kind of class II test with 8/20μs waveform.
1.3 Earthing Basic Requirement
1.3.1 Common Earthing
● Please use common earthing for base station system grounding, that is, device’s
AC working ground, DC working ground, protection ground, antistatic ground,
lightning protection ground share same ground grid, as shown in Figure Figure
2-1.

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设备
地排
接地总汇集线
VR
1层
2层
3层
避雷针引下线
接地引入线地面
地下
地网
避雷针
设备
地排
地排
Lightning Conductor
3rd Floor
2nd Floor
1st Floor
Ground
Underground
Ground Grid
Earthing Connection
Earthing Concentration Cable
Earthing Bar
Device
Device
Earthing Bar
Earthing Bar
LightningEarthingCable
Figure 2-1 Common Earthing

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● Typical mobile communication base station ground grid components are shown
in Figure Figure 2-2.
铁塔地网 设备地网
变压器
地网
垂直接地体连接扁钢
Tower Ground
Grid
Device Ground
Grid
Connecting Flat Steel Vertical Grounding Point
Transformer Ground
Grid
Figure 2-2 Typical Mobile Communication Base Station Ground Grid Components
● Ground grid should have test point at proper position, for ground resistance
test. There should be anti mechanical damage measures for ground breaking
part of grounding cable, such as steel pipe coverage or other mechanical
strengthening methods. And there should be anticorrosion measures, such as
anti-corrosion paint or tar. Steel protection pipe is shown in Figure 2-3.
图 2-3 Steel Protection Pipe for Ground Connection Cable
● When mobile station is in areas with soil resistivity below 700 Ω • m, power
frequency resistance of base station ground grid should be within 10 Ω. When
base station is in areas with soil resistivity above 700 Ω • m, there is no limit to

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base station power frequency resistance, but please make sure that effective
radius of ground grid is no less than 20m, and please deploy 20m~30 m star
shape horizontal grounding at the four corners of ground grid.
● Typical earthing system is shown in Figure 2-4.
Ground
Grid
Ground
Device
Figure 2-4 3D Earthing System
1.3.2 Power Supply System
1.3.2.1 Transformer Earthing
● If power transformer is in equipment room, please use the ground grid of
equipment room and tower as its ground grid.
● If power transformer is outside equipment room, and it locates within 30 m
from the edge of equipment room ground grid, please weld transformer ground
grid to equipment room or tower ground grid for every 3m~5m (at least 2
connections) to form a closed loop ground grid. When it locates more than 30 m
from ground grid edge, interconnection is not required.

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1.3.2.2 Commercial Power Supply
● Please use underground power cable instead of long distance aerial power cable,
as shown in Figure 2-5:
Equipment
Room
Bad Example of Long Distance
Aerial Cable Entrance
Figure 2-5 Bad Example of Long Distance Aerial Power Cable
● For high voltage power cable entering office site, please make sure that the
underground part is more than 200m. For low voltage power cable entering
office site, please make sure that the underground part is more than 15m (When
high voltage power cable goes underground, there is no limit to underground
length for low voltage power cable). When there is difficulty for cable to go
underground, please increase the grade/class of power system’s first level
overvoltage protection device.
● For cables with metal protection coat or shielding coat, please connect metal
protection coat to ground. Please use cable connecting device in cable
distribution box for grounding, aerial power cable is strictly prohibited.
● Please put cables without metal protection coat inside underground pipe and
have proper grounding at both ends of steel pipe.
● Please refer to Table 9.3.6 in YD5098-2005 for mobile base station electric
power SPD maximum electric current capacity parameter.
● Please deploy lightning protection measures for 4 wires of AC power (L1, L2,
L3 and N). In TT powering mode, electric power lightning protection device
uses 3+1 installation mode, which is to use 3 voltage-limiting lightning

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protection devices between L and N, 1 gap lightning protection device between
N and PE, as shown in 图 2-6.
被
保
护
设
备
L1
L2
L3
N
B级SPD
ProtectedDevice
B Class SPD
图 2-6 TT Power System 3+1 Lightning Protection Mode
● For AC power cabinet, please use C grade lightning protection device with
capacity of no less than 40 kA.
1.3.3 Equal Potential Connection
● Please use equal potential connection in device interconnection.
● Equal potential connection can use constant state equal potential connection
(for example, equal potential ring, shown in Figure Figure 2-7), or transient
state equal potential connection (SPD).

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接地网
4层
3层
2层
1层
环形接地排/均压排
设备
Ground Grid
Device
Ring Grounding Bar
Equal Potential Bar
1st Floor
2nd Floor
3rd Floor
4th Floor
Figure 2-7 Constant State Equal Potential Connection
1.3.4 Device Protection Ground Cable
● When using multi-core copper protection ground cable, please use whole cable
and cut off the extra, and please do not wind cable in circle.
● Please use 40mm x 4mm zinc coated flat steel bar for outdoor ground cable
whenever possible, to protect against rodent and theft, and reduce self inductive
resistance, please refer Appendix C for conductor induction calculation.
● Except for purposely designed inter-cabinet equal potential connection, please
do not connect protection ground cable between cabinets in series, as shown in
Figure Figure 2-8.

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地排
等电位连接
NodeB
地排
NodeB
NodeB
NodeB
不得串接
保护
Equal Potential Connection
Grounding Bar Grounding Bar
Please do not use
protection Connection
In Series
Figure 2-8 Equal Potential Connection
● Please use 1 grounded bolt in indoor earth grounding bar for 1 protection
ground cable only to avoid connector loosening when large current flows
through, and to facilitate field installation and maintenance.
● Please connect device protection ground cable directly to ground without fuse
or switch in between.
● Please connect outdoor earth grounding bar and indoor earth grounding bar to
earth separately, and do not connect them in serial.
● Please use shortest connection path to reduce ground potential rise as long as all
ground bonding cables meet engineering design goal.
● When connecting cable with copper bar, please polish surface of copper bar to
get rid of oxide, and coat it with oil for anti-corrosion, as shown in Figure 2-9.

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Figure 2-9 Anti Corrosion for Grounding Copper Bar
1.3.5 Cabling Requirement
● In communication equipment room, please keep device signal cable away from
AC power cable, antenna feedback cable. When placing them in parallel, please
keep them away from each other at the distance above 10cm. Please keep signal
cable and DC power cable away if possible. Large communication device
internal cabling follows the same principle, and cables should be bundled by
type, circled cable and random placement are strictly prohibited.
● Please keep AC office cable and lighting cable away from communication
device cable to facilitate check and maintenance in the future, as shown Figure
2-10.
Figure 2-10 Keep Lighting Cable Away from Communication Cable

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● Please place indoor signal cable between communication devices in the
middle of building whenever possible. For vertical cabling, keep away from
building column especially those at the 4 building corners whenever possible
(please keep distance above 5m). Please place signal cable inside closed metal
conduit for shielding, both ends of metal conduit connect to horizontal ground
bonding cable of equipment room separately.
● Please use relevant shielding measures for outdoor cables (for example, signal
cable and power cable) such as metal out layer or going through steel
shielding pipe with both ends connecting to ground. Please use special
earthing device for reliable earthing of shielding layer.
● Distance between electronic information system cable and other cable should
comply with GB50343-2004(Technical Specification of Lightning Protection
for Building’s Electronic Information System) as shown in Table 2-1.
Table 2-1 Distance between Electronic Information System Cables and Other Cables
Distance
Other Cables and Pipes
Electronic Information System Cables
Minimum Parallel
Distance(mm)
Minimum Cross Distance
(mm)
Lightning Protection Ground
Connection Cable
1000 300
Protection ground cable 50 20
Water Supply Pipe 150 20
Condensed Air Pipe 150 20
Heat Pipe(unsealed) 500 500
Heat Pipe(sealed) 300 300
Gas Pipe 300 20
Remark: When cable is above 6000mm, its nonparallel distance from lightning protection ground
connection cable should be calculated according to this formula:S≥0.05H in which:
H-Distance from ground for lightning protection ground connection cable at cross (mm)
S-Cross distance(mm)

19. 15
Chapter 2 Lightning Protection Theory
 Key Points
 Lightning Protection Basic Concept
 Lightning Protection Classification
2.1 Lightning Protection Concept
● Device’s Location in Various Systems
In engineering design, please specify device’s location in various systems
clearly, including physical location, location in electric power network,
lightning protection network and ground grid, and specify their interconnection
relations.
● Direct Strike Lightning Protection
Please keep device or systems within the protection area of external lightning
protection system to avoid direct strike lightning damage.
● Lightning Protection Measure Classification
Network system’s boundary protection is first level lightning protection,
communication device external interface protection is third level lightning
protection, and intermediate part protection is second level lightning protection.
● Lightning Protection Network Design
Lightning protection network design is to determine grade of network system’s
first level lightning protection, grade and location of second level lightning
protection, and parameters for each lightning protection level, to ensure
optimum protection for communication devices.
● Equal Potential Connection Requirement
If device’s interconnection interface has no surge protection grade, please use
equal potential connection for device working ground. If interconnected devices
do not support equal potential connection, their interconnected interfaces must
support required surge protection grade.

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● Voltage Sharing Equal Potential Principle
Interconnected devices should be in equal potential level of ground grid.
Otherwise, interconnected interfaces should have surge protection, and the
protection level should be suitable for transient voltage difference between 2
equal potential levels.
● Surge Protection Device Selection Principle
Please use surge protection product certified by lightning protection product
quality certification organizations approved by information industry
administrative authority.
● Ground Grid Design
Please eliminate ground potential back strike in ground grid whenever possible.
If there is risk of damage from ground potential back strike, please use equal
potential connection whenever possible.
● Electric Current Discharge Path
Each level of lightning protection device has different discharge capacity.
Please discharge large current as soon as possible. Please calculate each level’s
discharge capacity, path and possibly induced ground potential rise carefully, to
prevent large current from entering discharge path with small capacity.
● Electric Power Network Design
Please use electric power system compliant with engineering design for
network systems. Otherwise please take additional measures such as voltage
stabilizer, filters or UPS.
● Lightning Protection System Maintenance and Check
Please make overall check for lightning protection system’s regularly, normally
once before thunder storm season (for example at the end of March) and once
after thunder storm season (for example at the end of October) a year. Checking
items include: connection status of each ground cable (loosening or corrosion in
connecting point, bonding impedance increase), external lightning protection
box damage and deterioration, internal lightning protection module damage and

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deterioration. Please repair deteriorated connection and replace damaged or
deteriorated lightning protection box or module immediately.
Get average annual thunder storm days from local weather forecast station’s
data.
2.2 DifferentLevel of Lightning Protection Measures
According to lightning protection zone classification in IEC 62305(Protection against
Lightning Electromagnetic Pulse), there are 3 lightning protection zones for important
system. If one only uses single level lightning protection, very large lightning current
will lead to large residual voltage even after discharge, and device damage. And limited
protection capacity will also lead to device damage. Multi-level power system
protection can handle various overvoltage situations such as lightning and surge.
System boundary protection is first level lightning protection, communication device
external interface protection is third level lightning protection, intermediate part
protection is second level lightning protection.
2.2.1 First Level Lightning Protection
First level lightning protection level is determined by factors such as power cable
entering condition, local lightning strength, importance of system. It is normally used
in power cable entrance place of main power distribution box in equipment room.
According to GB50057-94(Building Lightning Protection Design Guide), external
metal cable to the building must go through more than 15m of underground metal
conduit before it enters the building, and low voltage lightning protection device must
be installed at building’s cable entrance gate. Please discharge high voltage induced by
external cable to protect connected devices.
Main lightning protection device for power entrance part of customer’s entire system or
the entire building should have current discharge capacity of more than 100 kA in
areas with frequent lightning, so that it can limit lightning overvoltage of tens of
thousands or even hundreds of thousands of voltage to thousands of voltage. Please
install lightning protection device in parallel at main power entrance part of
customer’s power distribution room or the entire building. Please install lightning

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protection device at this level in parallel, and there is no power limit for connected
devices.
2.2.2 Third Level Lightning Protection
Third level lightning protection grade is determined by device.
This is the most neglected aspect in systematic lightning protection. Breakdown
voltage for modern electronic device is normally tens of voltage, and maximum
working current for modern electronic device is at the level of mA. If there is no
second level lightning protection, residual lightning voltage entering devices via first
level lightning protection is still more than one thousand voltage, which will have great
impact on connected devices and will damage devices. Third level lightning protection
device should have lightning current discharge capacity of more than 10 kA.
For single phase electronic devices, please use socket type lightning protection device
as third level electric power lightning protection device, which is installed at the front
end of device in series and is excellent for protection against internal generated
operational overvoltage (such as startup or turnoff of inductive or capacitive device)
and high voltage electrostatic. For internal server and workstation，please use socket
lightning protection device with network protection interface and use socket with
lightning protection function for third level electric power and network interface,
which can protect against lightning strike to server and workstation via various
channels, and is a comprehensive solution.
2.2.3 Second Level Lightning Protection
Grade of second level lightning protection is determined by factors such as relations
between parameters of first level lightning protection and third level lightning
protection, lightning protection path length and requirement of relevant devices such as
power cable entrance part of UPS.
According to electric power lightning protection required by first level lightning
protection, electric power cable to building must use low voltage lightning protection
device. Even if there is first level lightning protection device in customer’s main
electric power cable entrance part uses, when current is large, although first level
lightning protection device can discharge via earth cable most of lightning current,
remaining lightning residual voltage is still rather high. First level lightning protection

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device can reduce wide spread lightning damage, but it can not guarantee the safety of
connected devices, so we need to install second level electric power lightning
protection device at electric power entrance part of main equipment room.
Second level lightning protection device, or intermediate level lightning protection
device, can limit overvoltage from thousands of voltage to a little more than one
thousand voltage. In areas with frequent lightning, please use protection device with
current capacity of 40 kA, to discharge the residual lightning voltage after first level
lightning protection discharge and induced lightning current in electric power cable.
Please install the lightning protection device in parallel at power entrance part of main
equipment room. Please install the lightning protection device in parallel before power
distribution cabinet, and there is no power limit for connected devices.
Lightning protection system is shown in Figure A-1.
System’s Lightning Protection Diagram
Satellite Antenna Lightning Conductor
Server
Switch
Ground
Connection
Power Cable
Office
Receiver Power Distribution Room
2nd Level
Power Protection
3dr Level
Surge Protection
Main Power
Distribution Room
1st Level
Power Protection
Office Office Office Office
Building Ground
Cable Protection
Antenna Protection
1st Level
Signal (Network)
Protection
2nd Level
Signal (Network)
Protection
Signal/Network Cable
Equal Potential
Connection Bar
Figure A-1 Lightning Protection System

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