Corrosion; Electromagnetic And Radio Frequency Interference - Cisco 4948 - Catalyst Switch Installation Manual

Site Requirements

Corrosion

Corrosion of system connectors is a gradual process that can eventually lead to intermittent failures of
electrical circuits. The oil from a person's fingers or prolonged exposure to high temperature or humidity
can corrode the gold-plated edge connectors and pin connectors on various components in the system.
To prevent corrosion, avoid touching contacts on boards and cards, and protect the system from extreme
temperatures and moist, salty environments.

Electromagnetic and Radio Frequency Interference

Electromagnetic 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 like 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:
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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:
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To predict and remedy strong EMI, you may also need to consult experts in radio frequency interference
Note
(RFI).
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
Caution
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.
Catalyst 4948E and Catalyst 4948E-F Switch Installation Guide
2-6
Only operate the system with the chassis covers installed.
Ensure 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.
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.
Chapter 2 Preparing for Installation
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