Why do we need lightning protection and earthing?

Computers and networks are becoming more and more embedded in people's lives and work, and they also herald the advent of the digital and information age. The widespread use of these microelectronic network devices makes the issue of lightning protection increasingly important. Due to the high density, high speed, low voltage, and low power consumption characteristics of microelectronic devices, this makes them very sensitive to various electromagnetic disturbances such as lightning overvoltage, power system operating overvoltage, electrostatic discharge, and electromagnetic radiation. If protection measures are not adequate, significant damage can be suffered at any time and anywhere.

The need for lightning protection in the server room

Lightning strikes can produce different forms of damage, and the International Electrotechnical Commission has called lightning disasters "a major hazard of the electronic age", lightning strikes, induction lightning strikes, power spikes and other instantaneous overvoltages have become the culprits of damage to electronic equipment. From the analysis of a large number of cases of lightning strikes on communication equipment, experts believe that lightning electromagnetic pulse (LEMP) caused by lightning induction and lightning wave intrusion is the main cause of equipment damage in the server room. The principle of prevention is "overall defence, comprehensive management and multiple protection". The aim is to minimise the damage caused.

Design of lightning protection and earthing systems for server rooms

1、Lightning protection design

The  lightning protection  and earthing system is an important sub-system for the protection of weak precision equipment and machine rooms, mainly to guarantee the high reliability of the equipment and prevent the harm of lightning. The central server room is a place with very high equipment value, and once a lightning accident occurs, it will cause incalculable economic loss and social impact. According to GB50057 "Design Code for Lightning Protection of Buildings" and the relevant provisions of IEC61024-1-1 standard, the lightning protection level of the central server room should be set as a class II standard design.

At present, the main distribution room of the building provides the first level of lightning protection according to the lightning protection design code of the building, therefore, the second and third level of composite lightning protectors are configured in front of the mains power distribution cabinet in the server room of the network centre of this project.

The lightning protectors are individually modular and should have a failure warning indication so that when a module fails by lightning the module can be replaced individually without the need to replace the whole lightning protector.

The main parameters of the two or three levels of composite lightning protection indicators: single-phase flux flow is: ≥ 40KA (8/20μs), response time: ≤ 25ns

2、Grounding system design

National standard GB50174 "Computer Room Design Code" in the computer room should have the following four kinds of ground: DC ground, AC working ground, AC protection ground and lightning protection ground for computer systems.

The resistance of each earthing system is as follows：

Ø DC earth resistance of computer system equipment not greater than 1Ω。

Ø The earth resistance of the AC protective earth shall be no greater than 4Ω;

Ø The earth resistance of the lightning protection ground shall be no greater than 10 Ω;

Ø The earth resistance of the AC working earth shall be no greater than 4Ω;

1、Indoor equipotential connections in the server room

Set up a ring-shaped grounding sink in the server room, the equipment and housing in the server room using S-type equipotential connection form, connected to the grounding sink, with 50 * 0.5 copper platinum tape laid under the movable floor support, longitudinal and horizontal composition 1200 * 1200 grid-like, in the server room a week laid 30 * 3 (40 * 4) copper tape, copper tape with special grounding terminal, with braided soft copper wire all metal in the server room All metal materials in the room are earthed and connected to the building's protective ground.

All earthing wires (including equipment, SPD, trunking, etc.) and metal trunking lap jumper wires in the project should be short, flat and straight, and the earthing resistance should be less than or equal to 1 ohm.

2、Machine room shielding design

The whole room shielding using colour steel plate for six-sided body shielding, shielding plate before the use of seamless welding, wall shielding body each side with grounding sink grounding at least 2 places.

3、Grounding device design for the server room

Due to the high earthing resistance requirements of the server room, an additional artificial earthing device was added near the building. 15 galvanised angles were driven into the ground grid channel and welded together with flat steel and backfilled with a resistance reducing agent. Electrostatic grounding in the machine room was introduced using 50mm² multi-strand copper core wire through a pipe.

The grounding resistance of the grounding device is required to be less than or equal to 1 ohm.

Method of making the ground network of the machine room

1、 Production of standard grounding network

At a distance of 1.5~3.0m from the building, take the 6m*3m rectangular frame line as the centre, excavate a soil trench with a width of 0.8m and a depth of 0.6~0.8m, and pass through the middle of the two long sides, using L5 (5*50*50) galvanized angle steel with a length of 2.5m, and punch one vertically at each intersection at the bottom of the trench, for a total of 6-20, as a vertical grounding electrode;

Then use No.4 (4*40) galvanized flat steel to weld the six angles together as horizontal grounding electrode; then use No.4 galvanized flat steel welded in the middle part of the ground grid frame, leading out to the outer corner of the wall of the machine room, 0.3m high from the ground, as PE grounding end; finally lead out from the grounding end 16-50 square millimetres above the sheathed earth wire, along the wall into the interior, connected to the machine room isotropic grounding collection row.

2、Using building reinforcement as a grounding grid

When building a new or renovated plant room, use the reinforcement bars inside the concrete column into the ground as an earthing device. Select at least 4 main bars (diagonal or symmetrical bars) within the column, weld them through with oxygen and then weld them to two copper threaded pipes of M12 or more protruding from the column surface as the grounding end, lead to the server room and connect with the equipotential grounding sink, which can be located under the anti-static floor.

How do I do lightning protection earthing in the server room?

Earthing is the process of connecting a metal shell in a circuit to the earth to form an electrical circuit. The purpose is to make it easy for current to flow into the earth and to form a protection for people and equipment.

Methods of earthing:

DC ground suspension method i.e. DC ground is not connected to earth and is strictly insulated from earth;

DC earth grounding method, the potential point earth and network of digital circuits etc. in equipment such as computers.

Regardless of the form used, there must be a grounding bus, grounding ground staff, in this particular emphasis is recommended to use grounding buried grounding network plate, can better guide to the earth, grounding should pay attention to the following issues:

Ø Try not to short-circuit or mix the DC ground and AC working ground in the machine room;

Ø not allow AC lines to be laid in parallel with the DC ground to prevent interference or shorting;

Ø DC ground network should be installed under the floor, to facilitate side connection, i.e. to reduce the grounding resistance, to facilitate the drainage of current。

1、Grounding copper row

The grounding of the indoor plant room is carried out by means of a 30*5 (width*thickness in mm) copper strip, 10 cm high from the ground around the wall of the plant room and connected to the outdoor grounding bus. A small hole is drilled every 50 cm in the copper sheet to facilitate the earthing of the equipment distributed in each area of the room.

2、Copper grounding plate

The copper grounding plate is fixed to the floor using a 60mm wide (10mm thick) L-shaped copper plate, which is used as the general grounding for all facilities that should be earthed to the plant room.

3、Ground Network

If there is a raised floor in the server room, a 2.5mm multi-core bare copper wire should be wrapped around the raised floor pillar for the floor network.

Example of lightning protection and grounding project in the server room

1、Project situation

A data centre server room is located on the third floor of the building, with an area of about 1000m².

This project uses the TN-S system for power distribution and sets the grounding wire (PE) independently. The building joint earthing system is used and the earthing is required to be less than 1 ohm.

The server room is equipped with functional and protective earthing and shares a set of earthing devices.

1、Protective earthing, lightning protective earthing extension to the building。

2、M-grid type structure is used for the equipotential grid in the server room. The indoor equipotential practice in the server room is to lay equipotential copper tape 30 x 3mm² (equal pressure ring) under the floor of the server room and along the cabinets for one week. The copper tape is connected to the PE rows of the power distribution cabinets in the server room with ZR-BVR6mm2, and a 100*0.3mm² copper foil equipotential grid is set up. The ground of the power equipment in the server room, the shell of the power equipment, the non-electrified metal pipes, the shell of the metal cable trough, the shell of the computer equipment, the anti-static floor brackets, the ceiling keel, etc. must be reliably connected to the equipotential copper network with ZR-BVR6mm2. The machine room is equipped with equipotential terminal boxes, which are reliably connected to the building's comprehensive earthing terminal using ZR-BVR50mm² cables. The schematic diagram of the equipotential earthing in the server room is shown in Figure 1-1.

2、Lightning protection design ideas

A complete lightning protection programme includes both direct and inductive lightning protection. The building where the central server room is located already has protection against direct lightning strikes, so this programme only takes corresponding inductive lightning protection measures for the distribution system of the server room's electronic equipment.

The AC power distribution system of the project uses three levels of lightning protection:

The first level of protection is achieved by installing lightning protectors in the low-voltage distribution room of the building (achieved by the building).

The second level is the installation of B-level lightning protectors in the UPS input distribution cabinets to achieve the second level of lightning protection.

The third level is the installation of a Class C lightning protector in the UPS output column head distribution cabinet in the server room to achieve the third level of lightning protection.

A schematic diagram of the lightning protection design for the server room is shown in Figure 2-1:

3、Lightning protection design ideas

As network integration systems have many protection points and a wide range of areas, lightning protection schemes should be designed from an overall lightning protection perspective in order to protect buildings and electronic network equipment in all directions within buildings from lightning damage or to minimise lightning damage. Nowadays, comprehensive lightning protection is used. A comprehensive lightning protection scheme should include two aspects: protection against direct lightning and protection against induction lightning, without either of which is incomplete, flawed and potentially dangerous.

1、Protection against direct lightning strikes

If there is no direct lightning protection, according to IEC1312 estimates almost all lightning currents flow through the conductor type lines in and out of the building (such as power lines, signal lines, etc.) to invade the equipment, so the damage is very serious, so do a good job of direct lightning protection is to do induction lightning protection; direct lightning protection in accordance with the national standard GB50057 "Building Lightning Protection Design Code" design and construction, mainly using Lightning rods, nets, lines, strips and good earthing systems are used to protect the exterior of the building from lightning damage and to provide a relatively safe environment for people or equipment inside the building.

2、Protection of power supply systems

Statistical data shows that more than 80% of lightning accidents in microelectronic network systems are caused by lightning impulse overvoltage induced on the power lines connected to the system. Therefore, good protection of the power supply lines is a part of the overall lightning protection that cannot be ignored.

3、Protection for signalling systems

Despite the installation of lightning protection devices on external introduction lines such as power and communication lines, the normal operation of the network can still be affected or even completely damaged by lightning strikes that induce overvoltages in network lines (such as twisted pair). Lightning strikes generate huge transient magnetic fields and extremely strong induced lightning strikes are induced in metal lines within a range of 1 km, such as network metal links;

In addition, when power lines or communication lines transmit over lightning voltage, or when the building's ground system is cascading lightning strikes, the powerful transient currents generated are sufficient for the network transmission lines to induce overvoltages that can already damage the network at once. Even if the overvoltage is not particularly high enough to destroy the equipment at once, each overvoltage shock accelerates the ageing of the network equipment, affecting data transmission and storage, or even crashing, until it is completely damaged. Therefore, the lightning protection of network signal lines is a very important aspect for the overall lightning protection of network integration systems.

4、Equipotential connections

The central server room where the backbone switch of the integrated network system is located shall be provided with an equal pressure ring to electrically connect all metal objects in the server room, including cable shields, metal ducts, metal doors and windows, equipment housings and all metal ducts entering and leaving the building, and other metal components, to the equal pressure ring to equalise the potential.

5、Grounding

The use of joint earthing in the server room can effectively address the effects of rising ground potential. A qualified ground network is the key to effective lightning protection. The joint ground network of a server room usually consists of the foundation of the server room building (including ground piles), a ring grounding (body) device and a working (power transformer) ground network. For the lightning protection of sensitive data communication equipment, a good or poor grounding system is directly related to the effectiveness and quality of the lightning protection. If the ground network does not meet the requirements, the ground network conditions should be improved, appropriate expansion of the ground network area and improve the ground network structure, so that the lightning current as soon as possible to discharge, shorten the lightning current caused by the high overvoltage holding time, in order to achieve lightning protection requirements.

4、Lightning protection for power supplies

The lightning protection of the power supply system adopts a three-stage lightning protection approach. The lightning protection of the distribution box of the server room should take no less than two levels of protection (fine protection), both in the input set of the main distribution box of the server room to install a set of two-level lightning protector, in the output of the server room distribution box each way to install three-level lightning protector. In other words, the front end of the main switch in the distribution cabinet is installed with a two-level lightning protector, which saves space and plays a beautiful and easy-to-maintain role, and the front end of the main switch in the utility distribution cabinet and UPS distribution cabinet are installed with three-level lightning protectors to protect the equipment in the server room。

5、Grounding system

There are four types of earthing in this computer room, namely: DC logic ground for computers, AC working ground, safety protection ground and lightning protection ground.

1、Computer room earthing system

A copper grid is installed underneath the movable floor of the computer room to connect all the computer system non-electric shells in the computer room to the copper grid and introduce them to the earth. The grounding system of the computer room is a special grounding system, which is provided by the building and has a grounding resistance of ≤ 1Ω.

2、The specific practice of equipotential earthing in the server room:

Use 3mm x 30mm copper strip, cross-rowed into a square under the active floor in the server room, its intersection points are staggered with the position of the active floor support, the intersection points are crimped together and fixed with pad insulators under the copper strip. The distance from the wall in the server room is 400mm. 3mm x 30mm copper strips are used along the wall to create an M-type or S-type ground network, the joint between the copper strips is crimped with a 10mm dowel and then burned with copper solder. 35mm² copper cable leads to the joint grounding body of the building, thus forming a Faraday cage grounding system and ensuring that the grounding resistance is no greater than 1Ω.

Equipotential connection of the server room: the ceiling keel, wall keel, movable floor support, non-computer system pipes, metal doors, windows, etc. are all connected equipotentially and are respectively connected to the grounding copper network of the server room by means of a 16m m2 earth wire.

3、AC working earth

The grounding required for operation in the power system (neutral grounding of the distribution cabinet) should be no greater than 4 ohms. The neutral line connected to the neutral point of a transformer or generator directly earthed is called the zero line; one or more points on the zero line are electrically connected to the ground again called the repeated earth. The AC working earth is the neutral point reliably earthed. When the neutral point is not grounded, if a phase touches the ground and the person touches another phase, the human body is subjected to contact voltage will exceed the phase voltage, and when the neutral point is grounded, and the neutral point grounding resistance is very small, the human body is subjected to voltage equivalent to the phase voltage; at the same time, if the neutral point is not grounded, due to the neutral point to the ground stray resistance is very large, so the grounding current is very small; the corresponding protection equipment can not quickly cut off the power, the people and The equipment produces harm; the opposite is true.

4、Safety protection ground

The safety protection ground is a good grounding between the shells of all machines and equipment in the server room and the bodies (shells) of auxiliary equipment such as motors and air conditioning units and the ground, which should be no greater than 4 ohms. When the insulator of all kinds of electrical equipment in the machine room is damaged, it will pose a threat to the safety of the equipment and the operating and maintenance personnel. Therefore, the casing of the equipment should be grounded reliably.

5、Lightning protection ground

That is, the grounding of the lightning protection system in the server room, generally buried underground with horizontal connecting lines and vertical grounding piles, mainly to lead the lightning current from the lightning device to the grounding device, which should be no greater than 10 ohms.

The lightning protection device can be divided into three basic parts: namely, the flash catcher, the lead wire and the earthing device, the flash catcher is the metal conductor that receives the lightning current. This programme will only add the lightning protector lead wire and power distribution cabinet within the grounding copper connection. Grounding resistance ≤ 4 Ω is required.

6、Lightning protection design solutions

1、Protection against direct lightning strikes

The building where the server room is located already has lightning rods, lightning strips and other external lightning protection facilities, no more external lightning protection supplementary design. If there is no direct lightning protection before, you need to do lightning protection or lightning protection network on the top floor of the machine room, if the machine room is in the open area, depending on the situation, you also need to install lightning rods, lightning rods, lightning protection must be done to lead off the line, access to the ground network.

2、Lightning protection of power supply system

(1) For the protection of the power line of the network integration system, first of all, the power incoming line into the general distribution room of the system should be laid with metal-clad cables, and the two ends of the cable armour layer should be well grounded; if the cable does not have an armour layer, then the cable will be buried in steel pipes, and the two ends of the steel pipes should be grounded, and the length of the burial should be not less than 15 metres. The power lines from the main distribution room to the distribution box of each building and the distribution box of the floor of the machine room should be laid with metal armoured cables. This can greatly reduce the possibility of induced overvoltage on the power line.

(2), the installation of power supply lightning protector on the power line is an essential protective measure. According to the IEC lightning protection code on the requirements of the lightning protection partition, the power supply system is divided into three levels of protection.

(1) The power supply lightning protection box with a circulation capacity of 80KA~100KA can be installed on the low voltage side of the distribution transformer in the main distribution room of the system.

② Install a secondary power supply lightning protection box with a current capacity of 60KA~80KA in the main distribution box of each building;

③ Installing three-stage power supply lightning protection with a current capacity of 20~40KA at the power inlet of important equipment (such as switches, servers, UPS, etc.) in the server room;

④ Use socket-type lightning protectors at the power supply of hard disk recorders and TV wall equipment in the control centre of the server room.

All lightning protectors should be well grounded. The lightning protector should be selected to pay attention to the form of the interface and the reliability of the grounding, important places should set up a special grounding line, do not connect the lightning protection grounding line and lightning rod grounding line, and as far away as possible, separate into the ground.

3、Lightning protection for signal systems

(1) The main network transmission lines used are optical fibre and twisted pair cables. Fiber optic does not require special lightning protection measures, but if the outdoor fiber is overhead, then the metal part of the fiber needs to be grounded. And twisted pair shielding effect is poor, so the possibility of induction lightning strike is relatively large, such signal lines should be laid in the shielded wire slot, shielded wire slot should be well grounded; can also wear metal pipe laying, metal pipe should be the whole line to maintain electrical connectivity, and metal pipe ends should be well grounded.

(2), the installation of signal lines on the signal lightning protection, induction lightning is a proven method. For network integration system, special signal lightning protectors can be installed before the network signal line enters the WAN router; signal lightning protectors with RJ45 interface (such as RJ45-E100) can be installed at the signal line entrance of the system backbone switch, main server and each sub-switch and server respectively. The selection of the signal lightning arrester should take into account the working voltage, transmission rate, interface form and so on. The lightning arrester is mainly connected in series at the interfaces of the equipment at both ends of the line.

① A single RJ45 port signal lightning arrester is installed at the server input port to protect the server.

② 24-port network switches are connected in series with 24-port RJ45 port signal lightning arresters to avoid damage to equipment due to lightning induction or electromagnetic field interference along the twisted pair.

③ Install a single RJ11 port signal arrester on the DDN dedicated line receiving equipment to protect the equipment on the DDN dedicated line.

④ Install a coaxial port antenna lightning arrester at the front of the satellite receiving equipment to protect the receiving equipment.

(3)、For the lightning protection of the monitoring system room

① Add a video signal lightning protector at the video line out of the DVR or use a rack-mounted video signal lightning protection box, 12-port full protection, easy to install.

② Add a control signal lightning protector (DB-RS485/422) at the control line entry end of the matrix and video splitter.

③ The telephone line of the machine room adopts the audio signal lightning protector, which is connected in series at the front telephone line of the telephone set, easy to install and maintain.

④ Install a control signal lightning protector at the front signal line access of the alarm to do effective lightning protection for the alarm signal line.

Note: All lightning protectors should be well grounded, the choice of lightning protectors should pay attention to the form of interface and grounding reliability, important places should be set up special grounding line, do not lightning grounding line and lightning rod grounding line, and as far away as possible, separate into the ground.

4、Equipotential connection in the server room

Under the anti-static floor in the server room, 40*3 purple copper rows are arranged along the ground to form a closed-loop grounding busbar. The metal shell of the power distribution box, power supply ground, lightning arrester ground, cabinet shell, metal shield line slot, doors and windows through the junction of each lightning protection area and the shell of the system equipment, as well as the isolation rack under the anti-static floor for multi-point equipotential grounding on into the sink. And the use of equipotential connection line 4-10mm2 copper core wire bolt fastening line clamps as connection materials. At the same time in the engine room to find out the building main steel, tested to ensure a good connection with the lightning belt, with 14mm galvanised round steel through the copper-iron conversion joint will be grounded busbar and connected to it. Formation of equipotential. The purpose of using a joint grounding network is to eliminate the potential difference between the various networks and to ensure that the equipment is not damaged by the lightning backlash.

5、Grounding network production design

Grounding is one of the very important aspects of lightning protection technology, whether it is direct or induction lightning, which ultimately introduces lightning currents into the earth. Therefore, for sensitive data (signal) communication equipment, no reasonable and good earthing system can reliably protect against lightning. Therefore, the ground network of buildings with a grounding resistance >1Ω needs to be rectified in accordance with the code requirements in order to improve the reliability of the grounding system in the server room. According to the specific situation, the effective area of the grounding network is expanded and the structure of the grounding network is improved by establishing different forms of grounding networks (including horizontal grounding bodies and vertical grounding bodies) along the server room building.

When a common earthing device is used, the common earthing resistance value should not be greater than 1Ω;

When a special grounding device is used, the grounding resistance value should not be greater than 4Ω.

The basic requirements are as follows:

1 ) to make a grounding network around the building, with less material and lower installation costs, to complete the most effective grounding device;

2 ) Grounding resistance value requirement R ≤ 1Ω;;

3) the earthing body should be set about 3~5m away from the main building where the plant room is located;

4) horizontal and vertical earthing body should be buried into the ground about 0.8m, vertical earthing body is 2.5m long, every 3~5m set a vertical direct earthing body, vertical earthing body adopts 50×50×5mm hot dip galvanized angle steel, horizontal earthing body choose 50×5mm hot dip galvanized flat steel;

(5) When welding the ground grid, the welding area should be ≥6 times the contact point, and the welded joints should be anti-corrosion and anti-rust treatment;

(6) The ground grid should be welded to the building column reinforcement at 0.6~0.8m below the ground, and corrosion and rust prevention treatment should be applied;

(7) soil conductivity is poor when using the method of laying resistance reduction agent, so that the grounding resistance ≤ 1Ω;;

(8) backfill soil must be a good conductive state of the new clay;

(9) with the building foundation ground network multi-point welding, and reserved for grounding test points.

The above is a traditional cheap practical grounding way, according to the actual situation, grounding network material can also choose new technology grounding device, such as maintenance-free electrolytic ion grounding system, low resistance grounding module, long-lasting copper clad steel grounding rod and so on.

7、Lightning protection and grounding considerations for the computer room

1, taking into account the interference of lightning or other telecommunications equipment, the computer room should not be set on the top floor of the building or against the outer wall, special circumstances limit, should be set up to prevent lightning interference. For particularly important computer systems, an independent shielded room should be considered. Building (including computer rooms) within the equipment and pipeline grounding installation should be carried out in accordance with the relevant specifications, good equipotential linkage;

2, to prevent lightning hazards should also prevent lightning-induced electromagnetic pulse, computer room distribution boxes should be set up SPD (anti-electromagnetic surge) protection devices to prevent the power supply to the server room due to lightning electromagnetic pulse caused by power failure. In addition, for the important system host, its communication cable should also be set up SPD protection device, because the number of communication cables is generally more, so the communication line protection settings should be set up according to the specific actual situation; reasonable;

3, the electrical earthing system should adopt TN-S earthing system, PE line and phase line are separated, the power access of the machine room should be made to repeat the earthing;

4, the grounding of the computer room is generally divided into AC working grounding, DC working grounding, safe working grounding, lightning protection grounding. According to the requirements of the Building Lightning Protection Design Code, when the lightning protection design uses a common grounding system, each grounding system should share a set of grounding devices. All exposed conductive objects of the information system (various boxes, shells, racks and other metal components) should establish a first-class potential connection network.

Therefore, the electrical lightning protection design should have a special equipotential linking row in the computer room, which is connected to the building's total equipotential linking row by means of a lead wire. According to the layer equipotential principle of the common earthing system, the use of the main structural reinforcement as a lead wire is more suitable for the common earthing system. It is also emphasised that the earthing resistance of the building earthing system should not be greater than 1Ω.