Lightning Protection and Grounding

Civil construction of the equipment room

The equipment room should be built of reinforced concrete.

The equipment room should be equipped with lightning protection devices, such as a lightning arrester.

The lightning protection ground for the equipment room (the grounding of the lightning arrester) should share the same grounding conductor with the protection ground of the equipment room.

AC power system (TN-S power supply recommended)

A dedicated transformer should be used at a communications station. Power cables that are connected to the communications station should be buried with metal jackets or insulated jackets passing through steel pipes. Both sides of the metal jackets or steel pipes are connected to the nearest ground bar. The length of the buried power cables should be no less than 15 meters.

The three phase lines at the low-voltage side of the AC transformer at the communications station should each be installed with a closed zinc-oxide lightning arrester for grounding. The enclosure of the transformer, AC zero wire of the low-voltage side of the transformer, and the metal outer protector of the power cable connected to the transformer enclosure must be connected to the nearest grounding post.

Incoming power cables

AC and DC power cables should not be led into or out of the communications station through overhead lines.

After low-voltage power cables are led into the equipment room, in the AC voltage regulator and AC power distribution box (PDB), install a lightning arrester for power cables and connect the lightning arrester to the nearest grounding post.

If the equipment room is located in an urban area, the AC power system of the equipment room should have a lightning protection unit with a nominal discharge current of no less than 20 kA. If the equipment room is located in a suburban area that is classified as a medium or high level lightning zone, install a lightning protection unit with a nominal discharge current of greater than 60 kA. If the equipment room is located in a mountainous area that is classified as a high-level lightning zone or in an isolated building in an urban area, install a lightning protection unit with a nominal discharge current of greater than 100 kA.

The ground cable of the lightning arrester used for the power supply must be shorter than one meter.

DC distribution grounding

The DC working ground of the communications station (the positive pole of the -48 V DC power supply or the negative pole of the 24 V DC power supply) should be led in from the nearest indoor main earthing conductor.

The device that supplies power to the communications station should provide the DC working ground that connects from the collective ground cable of the building (or from the protection ground bar in the equipment room) to the power supply.

Equipotential bonding

The communications devices and auxiliary facilities in the equipment room must be properly grounded. These devices and facilities include mobile base transceiver stations (BTSs), transmission devices, switching devices, power supply, and distribution frames. All the devices in the communications station should be grounded to the same ground busbar. All devices in the equipment room should be grounded to the same protection ground bar in the equipment room.

A ground grid must be shared by the working grounds and protection grounds of all devices in the equipment room.

The cable tray, iron suspension racks, racks, chassis, metal ventilation pipes, and metal doors and windows must be grounded.

Common grounding requirements

The neutral of the AC power cables must not be connected to the protection ground of any communications device in the equipment room.

Do not install switches or fuses on the ground cables.

Ground cables should be as short and straight as possible and should not be coiled.

Grounding resistance

Less than 1 Ohm

The upper end of the ground body must be no less than 0.7 m from the ground. In cold regions, the ground body should be buried under the frozen soil layer.

Measure the grounding resistance periodically to ensure that the grounding works properly.

Signal cable layout

No overhead signal cable should exist in the communications station. Signal cables should be led into the station from underground.

The communications cables led into or out of the communication station should be protected with metal sheaths or laid out in metal pipes.

The ground cable of a lightning arrester should be as short as possible. The unused wire pairs in the cables should be grounded in the equipment room.

Collective ground cable

The main earthing conductor can be a cable grounding ring or busbar.

Do not use aluminum materials as ground cables. Avoid electrochemical corrosion when different types of metals are interconnected.

Generally, a copper busbar with a cross-sectional area of no less than 120 mm² or galvanized steel with the same resistance is used as the main earthing conductor. The main earthing conductor must be insulated from the reinforcing steel bar in the building.

Grounding lead-in cable

The grounding lead-in cable must be no longer than 30 m. The grounding lead-in cable should use galvanized steel with a cross-sectional area of 40 mm x 4 mm or 50 mm x 5 mm.