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Examining Installation Site 49
Cleanness Requirements Dust is a hazard to the operating safety of the switch. The indoor dust
accumulated on the chassis can cause electrostatic absorption, which may result in
the poor contact of the connector or metal contact point. This happens more
frequently when indoor relative humidity is low, which will not only shorten the
service life of the switch, but also cause communication failure.
The required specifications on dust content and particle diameter in an equipment
room are shown in the following table.
Besides the dust specifications, the equipment room of the switch should also
meet the rigorous requirements for the content of salt, acid and sulfide in the air.
These harmful gases could accelerate the metal erosion and the aging process of
some parts. Incursion of harmful gases, such as SO
2
, H
2
S, NO
2
, NH
3
, and Cl
2
,
should be prevented. The specific limitation values of these harmful gases are
given in the following table.
Anti-Static
Requirements
Any possible interference sources, no matter outside or inside the system, affect
the switch in use in a way of capacitive coupling, inductive coupling,
electromagnetic radiation, common impedance (including the grounding system)
coupling or conducting line (power line, signaling line and transmission line etc.).
To prevent the interference, you should:
■ Take effective measures against electrical net interference for power supply
system.
■ Separate the working ground of the switch from the grounding device of the
power supply equipment or lightning-protection grounding device as far as
possible.
■ Keep the switch far away from the radio launcher, radar launcher, and
high-frequency devices working in the high current.
■ Adopt electromagnetic shielding if necessary.
Grounding
Requirements
A good grounding system is not only the basis essential to the stable and reliable
switch operation, but also an important guarantee of lightning protection,
anti-interference and ESD-prevention. The user must provide good grounding
system for the switch.
Table 66 Limitation on dust content in equipment room
Mechanical active material Unit Content
Dust particle particles/m
3
‚≤3 x 10
4
(No visible dust on desk in three days)
Note: Dust particle diameter ‚≥ 5µm
Table 67 Harmful gas limits in an equipment room
Gas Average (mg/m3) Max. (mg/m3)
SO
2
0.3 1.0
H
2
S 0.1 0.5
NO
2
0.004 0.15
NH
3
1.0 3
Cl
2
0.1 0.3