3
Table 2 Grounding and lightning protection requirements
Item Requirements
Grounding resistance
•
The grounding resistance is usually required to be less than 5 ohms, and less
than 10 ohms in an area with less than 20 thunderstorm days a year. If a
piece of angle steel is buried as the grounding conductor, the grounding
resistance is required to be less than 10 ohms. In an area with a higher
grounding resistance, reduce the grounding resistance by using brine or
resistance reducing agent around the grounding conductor.
•
The top of the grounding conductor must be a minimum of 0.7 m (2.30 ft)
away from the ground surface. In cold areas, the grounding conductor must
be buried below the frozen soil layer.
Grounding conductor
•
If a grounding strip is available, connect the yellow and green grounding
cable of the AP to the grounding strip. To make a grounding cable, make sure
the cable is with a cross-section area of a minimum of 6 mm2 (0.01 in2) and a
length of no longer than 3 m (9.84 ft).
•
If no grounding strip is available, bury a piece of angle steel/steel tube a
minimum of 0.5 m (1.64 ft) long in the earth to act as the grounding conductor.
In the case of a piece of angle steel, the size must be a minimum of 50 × 50 ×
5 mm (1.97. × 1.97 × 0.20 in); in the case of a piece of steel tube, it must be
zinc-plated and have a wall thickness of a minimum of 3.5 mm (0.14 in). Weld
the yellow and green grounding cable of the AP onto the grounding conductor
and use anti-erosion treatment on the welding joint. With a cross-section area
of a minimum of 6 mm2 (0.01 in2), the grounding cable must be as short as
possible and must not be coiled.
•
Make sure that the grounding terminals of all the lightning arresters of the AP
and the peer device of the AP are reliably grounded.
Grounding lead-in
A grounding lead-in is a metal conductor connecting a grounding net and a
grounding strip. The grounding cable of the AP must be connected to the
grounding strip. The grounding lead-in must be 30 m (98.43 ft) or shorter. A piece
of zinc-coated flat steel with a cross-section area of 40 × 4 mm (1.57 × 0.16 in) or
50 × 5 mm (1.97 × 0.20 in) is recommended. Connect the grounding strip and the
grounding lead-in of the AP through the yellow and green grounding cable with an
area of 35 mm
2
(0.05 in
2
), or weld them directly. Use anti-erosion treatment on the
welding joint.
Power grounding (AC)
•
Use a power cord with a protective earth (PE). Do not use a power cord with
only an L line and an N line.
•
The neutral line of the power cord must not be connected with the PGND of
other communications equipment. The L and N lines cannot be connected.
Lightning rod
•
The lightning protection grounding (for example, the grounding of the
lightning rod) must be connected to the grounding conductor of the
equipment room.
•
The lightning rod must be tall enough to protect the AP and its antennas.
•
In plain areas, the shielding angle of the lightning rod must be less than 45
degrees. In mountainous areas or lightning areas, the shielding angle must
be less than 30 degrees.
Outdoor antenna
The antenna support is already prepared according to the design requirements.
Network cable
•
Use a shielded twisted pair cable for outdoor installation. Make sure that the
devices at the two ends of the cable are reliably grounded.
•
If a metal tube is used, make sure the network cable is reliably grounded at
both ends of the tube.