2 Terms
2.0.1 Lightning protection zones（LPZ）
A zone easily to be affected by lightning stroke is classified to be the protected zones in accordance with the differences of the inside and the outside of buildings，environments of telecommunication rooms and protected equipment of telecommunication bureaus（stations）.Such protected zones are called the lightning protection zones.
2.0.2 Thunderstorm day
A thunderstorm day means one day when more than one thunder may be heard.
2.0.3 Low keraunic zones
Low keraunic zones are those areas where the average number of thunderstorm days in one year is no more than 25.
2.0.4 Middle keraunic zones
Middle keraunic zones are those areas where the average number of thunderstorm days in one year is within a range of 26-40.
2.0.5 High keraunic zones
High keraunic zones are those areas where the average number of thunderstorm days in one year is within a range of 41-90.
2.0.6 Strong keraunic zones
Strong keraunic zones are those areas where the average number of thunderstorm days in one year is more than 90.
2.0.7 Keraunic zones
The keraunic zones are classified into low keraunic zones，middle keraunic zones，high keraunic zones and strong keraunic zones according to average numbers of annual thunderstorm days.
2.0.8 Evaluation of lightning strike risk It is a method to have comprehensive evaluation on extent of damage of the bureaus（stations）due to lightning stroke to the earth and then determine levels and classes of protection，in accordance with various factors of lightning stroke.
2.0.9 Direct lightning flash
It is a flash directly attacking buildings or lightning protection systems.
2.0.10 Direct stroke protection It is a measure to protect buildings，structures，electric networks or electrical installations from being attacked by direct lightning flash.
2.0.11 Air-terminal system
It includes lightning rods，lightning strips（conductors）and lightning protection nets that receive lightning stroke directly.
2.0.12 Rolling sphere method
It is a simplified analysis method by applying the electric geometric theory to lightning protection analysis of buildings.
2.0.13 Down-conductor system
It is a metal conductor connected to the air-terminal system and the earth-termination system.
2.0.14 Lightning electromagnetic pulse（LEMP）
It is an electromagnetic radiation having relationship with lightning discharge.The electric field and the magnetic field generated thereby will be coupled to the electric or electronic system，thus destructive surge current or surge voltage will be produced.
2.0.15 External lightning protection system
Comprised of an air-terminal system，a down-conductor system and an earth-termination system，it is mainly used as a protection device to prevent direct lightning flash.
2.0.16 Soil resistivity
It is a parameter representing the conductivity of soil of which the value is equal to the resistance measured at two opposite faces of unit cube of soil.The unit thereof is Ω·m.
2.0.17 Power frequency ground resistance
It is the resistance between the earth electrode and the remote earth，when the power frequency current passes an earth-termination system.Its value is equal to thespecific value between the voltage of the earth-termination system to the remote earth and the current flowing to the earth via the earth electrode.
2.0.18 Common earthing
It is an earthing method where different earthing methods for various telecommunication equipments at telecommunication bureaus（stations），including working earthing of telecommunication equipment，protective earthing，shield earthing，static electricity protection earthing，logic ground of information equipment，and etc.are combined with the protective earthing of metal components of buildings and lightning protection systems and SPD，which shares，together with the lightning protection and earthing system of the buildings，the basic earth electrodes and external earthing systems.
2.0.19 Earth electrode
It is a piece or a group of conductor（s）closely contacting with the soil（the earth）to provide the electrical connection with the soil（the earth），for the purpose of connecting to the earth.
2.0.20 Earthing connection
Earthing connection means the connecting line between the earth electrode and the main earthing bar.
2.0.21 Earthing system
It is a complex system covering all electric connections and devices for earthing of systems，appliances and equipment，which include earth electrodes in the earth，earthing conductors，and cable shielding layers connected to earth electrodes，and equipment shells connected to earth electrodes or exposed metal components，rebars or frames of buildings and so on.
2.0.22 Earth grid
It is a group of earth electrodes comprised of bare conductors which are interconnected in the earth，for the purpose of providing common earth for electrical equipments or metal structures.
2.0.23 Earth-termination system
It is an aggregation of earthing conductors and earth electrodes.
2.0.24 Equipotential bonding
Connect the separated devices and various conductive objects using equipotential bonding conductors or SPDs，so as to reduce the potential difference among them caused by lightning current.
2.0.25 Equipotential bonding network
It is a network comprised of equipotential bonding conductors by which various exposed conductive parts of one system are connected.
2.0.26 Earthing reference point（ERP）
It is the only one connection point between the common earthing system and the equipotential bonding network of system.
2.0.27 Main earthing conductor
It means the strip copper bar or the steel flat used as the earthing conductor，which is usually used as the trunk line of the earthing system inside the telecommunication bureaus（stations），and by methods of laying，it can be classified into the horizontal main earthing conductor，the vertical main earthing conductor，the ring main earthing conductor or the bar-type main earthing conductor.
2.0.28 Earthing terminal
It is the connection terminal of earthing conductor or the earthing bar.
2.0.29 Earthing bar
It is connected with the earthing bus，and used as the rectangular copper bar for connection terminal of various earthing conductors.
2.0.30 Main Earthing Terminal（MET）
It is the earthing bar to connect various earthing conductors with the earth-termination system，and it is also the first stage earthing bar of the system.
2.0.31 Floor earthing bar（FEB）
Earthing bars mounted at each floor in buildings are used for the purpose of equipotential bonding by local earthing bars.
2.0.32 Local earthing bar（LEB）
It is the earthing bar being used inside the equipment room of telecommunication system for the purpose of local equipotential bonding.
2.0.33 Cable entrance earthing bar（CEEB）
It is an earthing bar to connect outdoor cables of cable entrance facility with main earthing terminals or ring earth electrodes.
2.0.34 Cable entrance facility（CEF）
It is a facility to connect the built-in earthing of cable with the metal skin for the purpose of earthing，and it shall be as close to the entrance of outdoor cable as possible according to the practical situation.
2.0.35 Common DC return（DC-C）
It is a DC power system which allows the DC return conductor to have multipoint connection with surrounding bonding networks.
2.0.36 Isolated DC return（DC-I）
It is a DC power system which allows the DC return conductor to have single-point connection to BN.
2.0.37 Common bonding network（CBN）
It is the main method for connection and earthing at telecommunication bureaus（stations），a group of metal parts which are interconnected with special intention or by accident and used for main bonding network of buildings.
2.0.38 Vertical riser（VR）
It is a group of vertical conductors providing a low-resistance engineering path between the telecommunication equipment and main earthing terminals，which run through vertically the earthing trunk lines at each floor of telecommunication bureaus（stations）.
2.0.39 Lightning over-voltage
It is the transient overvoltage occurring at system ports，which is caused by lightning discharge.
2.0.40 Surge protective devices（SPD）
SPDs are devices used to protect various telecommunication systems at telecommunication bureaus（stations）in case of lightning over-voltage or operation over-voltage.
2.0.41 Voltage limiting type SPD
In general，the voltage limiting type SPD is comprised of metal oxide varistors or semiconductor protection devices，which must be used in telecommunication bureaus（stations）.
2.0.42 Maximum continuous operating voltage
It is the allowable maximum alternating voltage（rms）or direct voltage permanently applied to SPD.The value thereof is equal to the rated voltage.
2.0.43 Residual voltage
It is the voltage peak between terminals when the discharge current flows through SPD.
2.0.44 Residual voltage of SPD
It is the maximum voltage peak measured between SPD terminals，when the surge voltage with specific waveform and amplitude is applied.
2.0.45 Nominal start-up voltage
It is the starting voltage of metal oxide varistor，when a constant 1mA direct current is applied.
2.0.46 Nominal discharge current（In）
It indicates the index of SPD discharge capability，corresponding to the surge current of 8/20μs simulated lightning wave.
2.0.47 Maximum discharge current（Imax）
SPD will not be substantially damaged，and each line（single module）can pass through the maximum current peak with specific number of times and specific waveform simulated lightning wave.The maximum discharge current is 2.5 times of nominal discharge current.
2.0.48 Two-port SPD
It is a kind of SPD with independent I/O ports，between which a special series impedance is inserted.
2.0.49 One-port SPD
SPD is in parallel with protected circuit.For one-port setting，the input port and the output port can be divided.And no special series impedance is inserted between I/O ports.
2.0.50 Global positioning system（GPS）
It is a technology by integration of satellites and communication development，to measure time and distance by navigational satellites.