3Com 8814 Limitation on dust content in equipment room, Harmful gas limits in an equipment room

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.

Table 66 Limitation on dust content in equipment room

Mechanical active material	Unit	Content
Dust particle	particles/m3	‚≤3 x 104

(No visible dust on desk in three days)

Note: Dust particle diameter ‚≥ 5µm

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 SO2, H2S, NO2, NH3, and Cl2, should be prevented. The specific limitation values of these harmful gases are given in the following table.

Table 67 Harmful gas limits in an equipment room

Gas	Average (mg/m3)	Max. (mg/m3)
SO2	0.3	1.0
H2S	0.1	0.5
NO2	0.004	0.15
NH3	1.0	3
Cl2	0.1	0.3

Anti-StaticAny possible interference sources, no matter outside or inside the system, affect Requirements 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 A good grounding system is not only the basis essential to the stable and reliable Requirements 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.