05 Grounding Regulations

Installation Manual M900/M1800 Base Station Controller Table of Contents

Huawei Technologies Proprietary

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Table of Contents

Chapter 5 Grounding Regulations............................................................................................... 5-1 5.1 About This Chapter ............................................................................................................ 5-1 5.2 Introduction to Grounding .................................................................................................. 5-1

5.2.1 Related Concepts of Grounding.............................................................................. 5-1 5.2.2 Types and Methods of Grounding........................................................................... 5-2

5.3 M900/M1800 BSC System Grounding .............................................................................. 5-6 5.3.1 Grounding of Assembled Cabinets ......................................................................... 5-7 5.3.2 Grounding of BSC Equipment................................................................................. 5-7 5.3.3 Connection Between BSC and Transmission Equipment..................................... 5-10 5.3.4 Grounding Resistance........................................................................................... 5-10

5.4 Reconstruction of Network Equipment Grounding .......................................................... 5-10 5.5 Grounding Processing ..................................................................................................... 5-12

Installation Manual M900/M1800 Base Station Controller

Installation PreparationsChapter 5 Grounding Regulations


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Chapter 5 Grounding Regulations

5.1 About This Chapter

This chapter describes the regulations for grounding, including the following contents:

z Introduction to Grounding z M900/M1800 BSC System Grounding z Reconstruction of Network Equipment Grounding z Grounding

5.2 Introduction to Grounding

This section provides the concepts related to grounding and describes the types and methods of grounding.

5.2.1 Related Concepts of Grounding

Grounding is one of the key approaches to improving the electromagnetic compatibility of electronic equipments.

Proper grounding can suppress the negative effect of interference and the interference to the outside. Improper grounding may generate severe interference, affecting the operation of equipments.

Grounding requirements vary with the equipment type and working environment.

There are two meanings for "Ground" in electronic equipments:

z System Reference Ground

It refers to the reference conductor of the signal loop or the reference electric potential of the zero voltage of the system power supply, that is, "system ground".

z Earth

It means the grounding device, consisting of metal cases and cables of electronic equipment. It is connected to the earth through grounding cables and grounding poles (bars).

Grounding stated in this manual refers to "connected to the earth".

The purpose of grounding is to:

z Ensure safety.




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According to the electric application rules, you must earth the metal case of electronic equipment to avoid danger caused by insulation failure or electric leakage.

z Suppress interference.

The connection of the system ground of electronic equipment to the earth can provide a stable reference potential for the signal loop. The connection of the shielding layer to the earth can suppress the interference of the varying electric field.

5.2.2 Types and Methods of Grounding

Normally, many parts in electronic equipment need to be grounded. Most of them must be separated into a number of independent grounding subsystems according to loop attributes and grounding purposes. These subsystems are then connected together to make an overall grounding.

The common grounding subsystems include:

z Protection grounding cable

It is the grounding cable of the mental case of equipment.

z System grounding cable

It is the grounding cable of the reference conductor of the signal loop or zero voltage reference potential.

z Shielding layer grounding cable

It is the grounding cable of the shielding layers of cables and transformers.

These grounding subsystems are also called three types of grounding busbars. Each grounding subsystem has many types of grounding modes, as described later.

I. Protection Grounding

There are two grounding modes for the protection grounding of electric equipment:

z Zero-line protection

It mostly applies to the three-phase four-line power distribution system. Normally it works with the protection circuit. When a phase line contacts the case, there is a large short circuit current flowing back to the power supply through protection grounding. The protection circuit reacts to this and then cuts off the power.

z Protection ground

It normally applies to single-phase electric equipment or electronic equipment of small capacity.




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II. System Grounding

There are three types of system grounding modes in electronic equipment:

z Float grounding mode

It is not grounded to the earth but floats freely, as shown in Figure 5-1.

Electroniccircuitry

Power cable

System grounding cable

Electroniccircuitry

Electroniccircuitry

Figure 5-1 Float grounding mode

If the float grounding system has a large resistance to the ground and a small distribution capacitance to the ground, the interference current caused by the external common mode interference is small. Generally, this mode applies to a small control system or low speed device.

z Direct grounding mode

For large electronic equipment, distribution capacitance to the ground increases accordingly with the increase of working speed and the expansion of the equipment. When the system reference potential is unstable due to interference, displacement current occurs through the capacitance to ground. This affects the normal operation of the equipment.

In addition, when static induction or lightning strike occurs, very high potential difference is generated between the control loop and the mental case of the equipment. This possibly causes arc discharge or breakdown of the poorly insulated part. Thus, this mode generally applies to large electronic equipment or complicated systems.

z Capacitance grounding mode

The system is connected to the earth through a capacitance. The grounding capacitance provides a path to the ground for the high-frequency interference component. It can suppress the effect of the distribution capacitance, but it is still short-circuit for the low frequency. When a DC component or low frequency




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potential difference exists between the system ground and the earth, you can select this mode. The capacitance must have better high-frequency characteristics and voltage endurance. Generally, the capacitance is 2 nF to 10 nF.

III. Shielding Layer Grounding

The shielding layer of twisted-pair cable or coaxial cable used for signal transmission can protect the transmitted signals against external interference only when it is grounded to the earth. The shielding layer can only suppress static induction.

Figure 5-2 shows the principle of shielding layer grounding.

C2

C3EN C1 UN

C 1

C 2

B A AShielding

Figure 5-2 Shielding layer grounding

In Figure 5-2, A is the noise source. Its noise voltage is UN and capacitance C3. B is the inducted signal line. Its capacitance to the ground is C1 and that to A is C2. EN is the noise induction potential. It can be expressed in the following formula:

CC C

UN2

1 2+EN=

The shorter the distance between A and B is, the larger C2 and EN are. Nevertheless, if the shielding layer of the signal line B is grounded, the induced noise potential is always zero. Otherwise, the signal line can still be affected by partial induction potential due to the distribution capacitance existing between the shielding layer and the signal line.

In addition, the grounding of the shielding layer can suppress the signal line from radiating noise to the outside, as shown in Figure 5-2. If the shielding layer of the noise source A is grounded, its noise voltage to the earth is zero. Thus it cannot generate induction voltage to B.

The shielding layer made of non-magnetic conductive materials, such as copper and aluminum, can only suppress static induction noise. To prevent magnetic induction noise, you must use materials with strong magnetic conductivity, such as iron, for the shielding layer.




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For either system grounding or shielding layer grounding, one-point grounding mode is often used, that is, use a grounding pole. This is because grounding resistance exists. When the current flows to the earth, potential of the grounding pole and the earth around it increases, causing the potential change of the equipment ground. Therefore, potential difference always exists between two separate grounding points far away from each other, as shown in Figure 5-3.

U1 U2

O2O1

G2G1UN

IN

Signal line

Signal return line

Figure 5-3 Potential difference between two grounding points

The system grounds of two units U1 and U2 are connected to the earth at a nearby place respectively. Potential difference UN exists at the grounding points G1 and G2, thus generating interference current IN. Because of the effect of various factors, a great change takes place to the potential around the grounding pole.

For example, the voltage can be up to between 1 kV and 2 kV when there is a lightning strike. Therefore, the system has a large interference current instantly, thus affecting the normal operation of the system.

In addition, the system ground or the shielding ground forms a closed loop with the grounding cable and the earth. Interference current can be generated in the loop under the effect of magnetic induction. Therefore, one-point grounding mode often applies to the actual magnetic environment.

For high-frequency signal or interference, the shielding layer also uses the two-end grounding or multi-point grounding mode. This is because even a short grounding cable has great impedance and the voltage decreases at a high-frequency. Due to the effect of distribution capacitance, it is indeed difficult to use one-point grounding. Therefore, the two-end grounding or multi-point grounding mode is often used to reduce grounding impedance and eliminate distribution capacitance.

For example, when the length of the cable is 1/4 that of the signal wave, the signal generates standing wave on its shielding layer to form a noise transmission antenna. In this case, you must use the two-end grounding mode to suppress the noise transmission. Furthermore, the shielding layer of some sensitive high-frequency input




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cables must also use the two-end grounding mode to reduce the area of the grounding loop.

The small-capacity BSC must use the radiation one-point grounding mode, as shown in Figure 5-4. That is to connect all parts to the grounding pole through grounding cables. Thus interference due to common impedance and closed loop of grounding can be avoided.

U1 U2 U3

Figure 5-4 Radiation one-point grounding mode

When the system has many grounding cables, you can use the trunk grounding mode. That is to use a conductor with an enough cross-sectional area as the grounding busbar and connect it directly to the grounding pole. Then you can connect all parts to the busbar nearby, as shown in Figure 5-5.

U1 U2 U3

Figure 5-5 Trunk grounding mode

5.3 M900/M1800 BSC System Grounding

This section describes the grounding requirements for the BSC and introduces how to ground the components of the BSC.




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5.3.1 Grounding of Assembled Cabinets

I. General Rules

The general rules apply to the lightning protection and grounding design for Huawei BSC products, including the following contents:

z The lightning protection and grounding design must take into consideration the personal and equipment safety, and normal operation of communications equipment.

z The lightning protection and grounding design must also comply with relevant specifications.

z If there is difficulty in implementing some items of this regulation, you must detail the reasons in the design documents, and propose solutions for approval.

z Huawei is entitled to the interpretation regarding this regulation.

II. General Principle

The general principle includes the following:

z The grounding cable, as thick and short as possible, must use copper conducting wires to minimize high-frequency impedance.

z The grounding terminal must be secured with bolts to ensure good contact. z To reduce mutual interference, the grounding cables and signal cables cannot be

parallel or wound together. z The BSC system must use joint grounding. The grounding cables of the cabinets

in the same module must be securely jointed to form an equipotential body.

5.3.2 Grounding of BSC Equipment

I. Ground Interconnection in Cabinet

To ensure equal potential between the work ground (GND) and protection ground (PGND), three grounds must be combined into one on the top of the cabinet (This task is complete before delivery).

The rack and PGND must be connected through a short conducting wire before delivery. The cross-sectional area of the wire must be no less than 6 mm2. Fasten one end of the short conducting wire to the PGND terminal using nuts, and the other end to the rack body using bolts.

II. Ground Interconnection Between Cabinets

Ground interconnection between cabinets includes the following several cases:

z Ground interconnection between adjacent racks




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During installation, connect the racks in the same row using bolts and washers.

z Ground interconnection between cabinets on the cabinet top

To ensure equal potential for all the cabinets in the same module, connect the GNDs of the cabinets with each other using copper wires on the top of cabinets. The copper wires must be 25 mm2 in cross-sectional area and 1,400 mm in length, as shown in Figure 5-6.

z Busbar interconnection between cabinets

Connect the grounding cables of the cabinets in the same module using a short connecting wire. Ensure that the connecting wire is no less than 2 mm2 in cross-sectional area and 200 mm in length.

Connect the two ends of the connecting wire respectively to the GNDs of the busbars of adjacent cabinets, as shown in Figure 5-6.

z Ground interconnection when assembled and welded cabinets are combined

When assembled cabinets and welded cabinets coexist in the same module and are placed side by side, the +5 V GND of the power distribution box of the welded cabinet must be connected to the GND of the power distribution box of the assembled cabinet with a short conducting wire.

z Cabinet grounding

From each cabinet one GND wire and one PGND wire must be led out and connected respectively to the GND and the PGND copper bars of the DC distribution cabinet or power distribution box.

The GND copper bar of the DC distribution cabinet or power distribution box must be connected to the GND terminal of the DC distribution panel through the black plastic insulated copper core GND busbar. The PGND copper bar must be connected to the PGND terminal of the equipment room through yellow and green plastic insulated copper core PGND busbar.

The grounding cable of the cabinet must be no less than 25 mm2 in cross-sectional area. The cross-sectional area of the grounding busbar must be calculated based on engineering design. The cross-sectional area of the grounding busbar of the DC distribution cabinet must be no less than 240 mm2 and that of the power distribution box must be no less than 90 mm2.

Figure 5-6 shows the grounding of the assembled cabinet.




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(4) (4) (4)

-48V2

GND

PGND

(3)

-48V1

(1)

(2)

GN

D

-48V1

-48V2

PGN

D

GN

D

-48V1

-48V2

PGN

D

GN

D

-48V1

-48V2

PGN

D

......

......

......

......

(1) DC high resistance cabinet or power distribution box (2) To DC distribution panel (3) Protection grounding bar of the equipment room (4) Assembled cabinet

Figure 5-6 Grounding of assembled cabinets

III. Grounding of Signal Cables

The shielding layer of the HW cables or DT8K cables must be grounded at both ends.

IV. Grounding of the BAM

The power supply to the embedded industrial-computer BAM must be led in directly from the 48 V and GND of the BSC busbar to share the GND with the BSC.

The standalone server BAM using 220 V power supply must share the GND with the BSC through an inverter.

V. Grounding of the Alarm Box

The power supply to the alarm box must be led in directly from the 48 V and GND of the BSC busbar to share the GND with the BSC.

For the DC power supply of GM12 alarm box, the alarm box can support 110 V/220 V power. There is a three-phase socket at the lower right corner of the alarm box. To connect the DC power supply, only a three-phase socket is needed. The alarm box uses the grounding of the three-phase socket.

VI. Grounding of Terminal Equipment and Their Connection Cables

For the terminal equipment connecting the BSC, their AC power supply PGND must be connected to the shell of the BSC. That is, the PE end of the connector card must be




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disconnected from the AC neutral line and then connected to the grounding cable from the BSC GND.

5.3.3 Connection Between BSC and Transmission Equipment

The shielding layer of the cable connecting the BSC and the transmission equipment must be grounded at both ends. The transmitting end must be securely grounded while the receiving end can be disconnected.

5.3.4 Grounding Resistance

It is recommended that the grounding resistance of the telecommunication site where the base station equipment is located be less than 10 ohm. It must conform to the relative stipulation of the country.

5.4 Reconstruction of Network Equipment Grounding

This section covers grounding reconstruction for the installed equipment that does not comply with the grounding rules. For the sake of safety, grounding reconstruction must be performed when the traffic is low and the power supply is cut off.

To reconstruct the grounding of equipment, do as follows:

1) Back up data. 2) Cut off the power supply to the power supply unit in each frame in regular

sequence. 3) Turn off the air breakers on the upper front of the rack one by one. 4) Turn off the power switch of the cabinet through the power distribution cabinet or

power distribution box. 5) Remove the nut from the PGND connector post and push the lug at one end of the

0.19m GND feeder into the PGND connector post. 6) Remove the nut from the GND connector post and connect the lug at the other end

of the 0.19m GND feeder to the GND connector post. Meanwhile, connect the lug on one end of another connecting 1.4m GND feeder to this post and connect the other end to the GND connector post of the neighboring cabinet.

7) Ensure that the installation of lugs meet the requirements.

If you need to connect two or more cables to the same connector post, ensure that the lugs are not overlapped. You can use the cross installation or back-to-back installation mode. If they must be overlapped, ensure to curve the lugs for 45 or 90. Mount the larger one beneath the smaller one and then tighten them, as shown in Figure 5-7, Figure 5-8, and Figure 5-9.




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8) After all cable connections are complete, measure with a multimeter to see if there is any short circuit between the 48 V terminal and the GND before power-on again.

9) Turn on the power switch in the power distribution cabinet or power distribution box.

10) Turn on the air breakers on the upper front of the rack one by one. 11) Power on the power supply units in all frames in sequence. 12) Observe if every frame works normally.

Proceed with the reconstruction of the next rack.

Back-to-back installation

Flat washer

Nut

Spring washer

Figure 5-7 Installation of connectors (1)

Flat washer

Nut

Spring washer

Bending 45 or 90 degrees





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Flat washer

Nut

Spring washer

Cross installation


5.5 Grounding Processing

The grounding resistance must be as small as possible. During the engineering design, the grounding body is generally made of zinc-plated material and the length, width, and thickness must meet the grounding requirements of the BSC. For example, 50 mm x 50 mm x 5 mm angle steel, 2.5 m in length.

Factors that affect the grounding resistance include:

z Resistance of the grounding bar z Contact resistance among the connecting cables, grounding post, and soil z Soil type

The soil type has the greatest impact on grounding resistance. For areas in poor soil conditions, you can use some chemical agents such as acrylamide resistance reduction agent around the grounding bar to meet the grounding requirements of the BSC.

z Temperature

When the temperature is below 0C, the grounding resistance may change much. For the BSC installed in a cold area, you must mount grounding bars deep in the earth and use chemical agents.

z Humidity of soil

The connecting cables from the grounding bars to the grounding bolts on the BSC equipment must use copper core cables with the cross-sectional area no less than 50 mm2 and the distance between them as short as possible. When the distance is over 50 m, you must use the copper core cables with a larger diameter.




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You must tin both ends of the connecting cable or soak them in tin. Then clean the coating material, varnish, and paint around the fixing point to ensure good contact between the two metal surfaces.

All grounding parts must have anticorrosion protection. You must tighten the grounding bolts mechanically to ensure a low resistance connection.

Table of ContentsChapter 5 Grounding Regulations5.1 About This Chapter5.2 Introduction to Grounding5.2.1 Related Concepts of Grounding5.2.2 Types and Methods of Grounding

5.3 M900/M1800 BSC System Grounding5.3.1 Grounding of Assembled Cabinets5.3.2 Grounding of BSC Equipment5.3.3 Connection Between BSC and Transmission Equipment5.3.4 Grounding Resistance

5.4 Reconstruction of Network Equipment Grounding5.5 Grounding Processing

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05 Grounding Regulations