Operation Environment Requirements. Layout of Equipment Room. Lightening Protection and Grounding Requirements, страница 5

On structure of the equipment room

Build the equipment room with steel and concrete.

The equipment room should be equipped with facilities such as lightening arrester to protect it against direct lightening strokes.

Make sure the lightening protection grounding of  the equipment room, or that of devices such as the lightening arrester,  shares the same grounding body with the protection grounding of the building where the room is located in.

Use TN-S  for AC power supply

Equip the communication office with special electric transformers and metal-jacketed or insulation-jacketed power cable. The power cable is to pass through a steel pipe and buried in the earth before entering the office. Both ends of both the metal jacket and the steel pipe should be grounded by proximate. Make sure the buried length is no less than 15 meters.

Each of the three live cables at the low-voltage side of the AC transformer should be equipped with a gapless zinc oxide arrester respectively.  The chassis, the AC neutral cable of the low-voltage side, and the metal jacket of the cable connected to the chassis should all proximately grounded.

Equip the incoming power cable with a lightening arrester

Do not lead in/ lead out AC/DC power cables aerially for the office.

Equip the in-room low-voltage power cable with a lightening arrester in the voltage regulator or in the AC panel. The arrester should be grounded proximately.

If the office is located in the city, it is recommended to use an arrester with the nominal discharge current no less than 20 kA. If it is located in the suburb of intermedial lightening danger level or higher, an arrester with the surge current  higher than 60 kA is recommended. If located in an isolated huge building in the city or in the mountain area where  lightening strokes occur often, please use an arrester that has a surge current more than 100 kA.

The grounding cable should be less than 1 meter in length.

DC power supply grounding

The working ground of the office, that is, the anode of a -48 V DC power supply or the cathode of a 24 V power supply, should be led from the in-door grounding bus line by proximate. The grounding cable should satisfy the max load of the equipment.

The power supply facilities for the office are to possess a DC working neutral line, which is introduced from the general grounding bus line or the protection grounding bar of the equipment room.

Equipotential connection

All communication equipments and auxiliary equipments in the room such as the mobile base station and the transmitting, exchanging, power and distribution frame should be connected to the protection ground.

The protection grounding of all equipments in the communication office should share a same general grounding bar, while that of the same equipment room all connect to the same protection grounding bar.

The working ground and protection ground of the communication  equipment in the equipment room should adopt the joint grounding mode, that is, they share a same grounding network.

Protection grounding efforts should also be done to the indoor cable rack, equipment chassis, metal ventilation pipe, metal door or window.

General requirements on grounding

The AC neutral line is forbidden to be connected to the protection ground of any communication equipment.

Make sure there is no fuse, switch or other devices of the like on a grounding line.

All grounding lines should be as short and straightforward as possible. Make all efforts to avoid winding of  them.

On the grounding resistor

< 1Ω.

The upper end of the grounding body should be 0.7 meters or more underground. In cold areas, the grounding body should be buried in the frozen layer or lower.

Make regular monitor efforts on the grounding resistor to make sure the grounding is always valid.

On routing of the signal cable

Signal cables should be led into the communication office from underground. Aerial routing of signal cables is forbidden.

The leadin or leadout communication cable should be metal-jacketed. Otherwise, they should be routed in metal pipes.

The grounding cable of the arrester should be as short as possible. The empty pairs in the cable should be connected to the protection ground in the equipment room.

On the grounding bus line

The general grounding bus line can be grounding loop or bar.

The grounding cable should be not of aluminum material. If interconnection occurs between different metal connectors, take measures to avoid by electric chemical corrosion.

Generally, the cross-sectional area is a copper bar of no less than120 mm2 or zinc-plated flat steel of the same resistance. The grounding bus line should be kept insulated from the construction steel.

On the grounding lead-in wire

The grounding lead-in should be no longer than 30 meter. As for the material, it is recommended to use zinc plated flat steel  with the cross-sectional area being 40 mm x 4 mm or 50 mm×5 mm.