Cisco 4948 - Catalyst Switch Installation Guide download pdf (Page 34)

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Catalyst 4948E and Catalyst 4948E-F Switch Installation Guide

OL-21561-02

Chapter 2 Preparing for Installation

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:

• 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.

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.

Note To predict and remedy strong EMI, you may also need to consult experts in radio frequency interference

(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.

Caution 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.

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Cisco 4948 - Catalyst Switch Installation Guide Page 34