H3C Technologies H3C S9800 Series Switches - Manual (Page 10)

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• Lasting high relative humidity can cause poor insulation, electricity creepage, mechanical property
change of materials, and metal corrosion.
• Lasting low relative humidity can cause washer contraction and ESD and bring problems including
loose captive screws and circuit failure.
• High temperature can accelerate aging of insulation materials and significantly lower the reliability
and lifespan of the switch.
Cleanliness
Dust buildup on the chassis might result in electrostatic adsorption, which causes poor contact of metal
components and contact points, especially when indoor relative humidity is low. In the worst case,
electrostatic adsorption can cause communication failure.
Table 1 Dust concentration limit in the equipment room
Substance Concentration limit (particles/m³)
Dust ≤ 3 x 10 4 (no visible dust on the tabletop over three days)
NOTE:
Dust diameter ≥ 5 μm
The equipment room must also meet limits on salts, acids, and sulfides to eliminate corrosion and
premature aging of components, as shown in Table 2 .
Table 2 Harmful gas limits in the equipment room
Gas Maximum concentration (mg/m 3 )
SO
2
0.2
H
2
S 0.006
NH
3
0.05
Cl
2
0.01
EMI
All electromagnetic interference (EMI) sources, from outside or inside of the switch and application
system, adversely affect the switch in the following ways:
• A conduction pattern of capacitance coupling.
• Inductance coupling.
• Electromagnetic wave radiation.
• Common impedance (including the grounding system) coupling.
To prevent EMI, use the following guidelines:
• If AC power is used, use a single-phase three-wire power receptacle with protection earth (PE) to
filter interference from the power grid.
• Keep the switch far away from radio transmitting stations, radar stations, and high-frequency
devices to make sure the EMI levels do not exceed the compliant range.
• Use electromagnetic shielding when necessary. For example, use shielded interface cables.