Cisco Catalyst 6816-X-LE, Руководство по установке оборудования

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avoid touching contacts on boards and cards, and protect the system from extreme temperatures and moist,
salty environments.
EMI and Radio Frequency Interference
EMI and radio frequency interference (RFI) from a system can adversely affect devices such as radio and
television (TV) receivers operating near the system. Radio frequencies emanating from a system can also
interfere with cordless and low-power telephones. Conversely, RFI from high-power telephones can cause
spurious characters to appear on the system monitor. RFI is defined as any EMI with a frequency above 10
kilohertz (kHz). This type of interference can travel from the system to other devices through the power cable
and power source, or through the air in the form of transmitted radio waves. The Federal Communications
Commission (FCC) publishes specific regulations to limit the amount of EMI and RFI emitted by computing
equipment. Each system meets these FCC regulations. To reduce the possibility of EMI and RFI, follow these
guidelines:
• Always operate the system with the chassis covers installed.
• Ensure that all chassis slots are covered by a metal filler bracket and that an unused power supply bay
has a metal cover plate installed.
• Ensure that the screws on all peripheral cable connectors are securely fastened to their corresponding
connectors on the back of the chassis.
• Always use shielded cables with metal connector shells for attaching peripherals to the system.
When wires are run for any significant distance in an electromagnetic field, interference can occur between
the field and the signals on the wires. This fact has two implications for the construction of plant wiring:
• Bad wiring practice can result in radio interference emanating from the plant wiring.
• Strong EMI, especially when it is caused by lightning or radio transmitters, can destroy the signal drivers
and receivers in the chassis, and even create an electrical hazard by conducting power surges through
lines into equipment.
To predict and provide a remedy for strong EMI, consult experts in RFI.
Note
If you use twisted-pair cable in your plant wiring with a good distribution of grounding conductors, the plant
wiring is unlikely to emit radio interference. If you exceed the recommended distances, use a high-quality
twisted-pair cable with one ground conductor for each data signal when applicable.
Category 5e, Category 6, and Category 6a cables can store large levels of static electricity because of the
dielectric properties of the materials used in their construction. Always ground the cables (especially in new
cable runs) to a suitable and safe earth ground before connecting them to the module.
Caution
If the wires exceed the recommended distances, or if wires pass between buildings, give special consideration
to the effect of a lightning strike in your vicinity. The electromagnetic pulse caused by lightning or other
high-energy phenomena can easily couple enough energy into unshielded conductors to destroy electronic
devices. If you have had problems of this sort in the past, you may want to consult experts in electrical surge
suppression and shielding.
Catalyst 6840-X Switch Series Hardware Installation Guide
25
Preparing for Installation
EMI and Radio Frequency Interference