Cisco Systems SFS 7000D, SFS 7000P manual Dust and Particles, Corrosion

Chapter 2 Preparation for Installation

Site Requirements

Dust and Particles

Exhaust fans cool power supplies and system fan trays cool systems by drawing in air and exhausting air out through various openings in the chassis. However, fans also ingest dust and other particles, causing contaminant buildup in the system and increased internal chassis temperature. A clean operating environment can greatly reduce the negative effects of dust and other particles, which act as insulators and interfere with the mechanical components in the system. In addition to regular cleaning, follow these precautions to avoid contamination of your equipment:

•Do not permit smoking anywhere near the system.

•Do not permit food or drink near the system.

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

EMI and RFI from a system can adversely affect devices such as radio and 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 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 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:

•Operate the system only when the chassis cover is installed.

•Ensure that all expansion slots are covered either by a card-mounting bracket or by a metal filler bracket and that all drive bays have either a drive or a metal insert 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 might need to consult experts in RFI.

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