13
Grounding and lightning protection
Table 8
Grounding and lightning protection requirements
Item
Requirements
Grounding
resistance
The grounding resistance is typically required to
be less than 5 ohms, and less than 10 ohms in an
area that has less than 20 thunderstorm days a
year. If an angle iron is to be buried into the
earth as the earthing conductor, the grounding
resistance is required to be less than 10 ohms. If
the installation site has a high earth resistance
rate, it is recommended to spray some salt water
or resistance-reducing agent on the earth
around the buried earthing conductor to
reduce the resistance rate of the earth.
The top of the earthing conductor should be at
least 0.7 m (2.30 ft) away from the ground
surface. In cold areas, the earthing conductor
should be buried below the frozen soil layer.
Protection
grounding
If a grounding strip is available at the site, attach
the yellow-green PGND cable of the AP to the
grounding strip. The PGND cable must have a
cross-section area of at least 6 mm
2
(0.01 in
2
)
and a length not longer than 3 m (9.84 ft).
If no grounding strip is available at the site,
hammer a 0.5 m (1.64 ft) or longer angle iron or
steel tube into the earth. The angle iron should
be sized at least 50 × 50 × 5 mm (1.97 × 1.97 ×
0.20 in.); the steel tube should have a wall
thickness of at least than 3.5 mm (0.18 in.) and
be zinc-plated. Weld the yellow-green
grounding cable to the angel iron or steel tube
and treat the joint for corrosion protection. With
a cross-section area of at least 6 mm
2
(0.01 in
2
),
the grounding cable should be as short as
possible. Do not coil the cable.
Make sure the lightning arresters of all devices
and the peering devices connected to these
devices are well grounded.
Grounding
lead
The grounding lead is a metal conductor
connecting the grounding strip to the
grounding grid. The PGND cable of the device
should be attached to the grounding strip. The
grounding lead should not be longer than 30
m (98.43 ft). H3C recommends a zinc-plated
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)..
The grounding strip and the grounding lead
should be jointed using a 35 mm2 yellow-green
PGND cable or directly welded together with
the joint treated for corrosion protection.
