Plant Wiring; Interference Considerations; Distance Limitations - Cisco 7000 Hardware Installation And Maintenance

Site Requirements

Plant Wiring

Following are guidelines for setting up the plant wiring and cabling at your site. When planning the
location of the new system, consider the distance limitations for signaling, electromagnetic
interference, and connector compatibility, as described following.

Interference Considerations

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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Note
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. When exceeding the recommended distances,
use a high-quality twisted-pair cable with one ground conductor for each data signal.
If wires exceed recommended distances, or if wires pass between buildings, give special
consideration to the effect of a lightning strike in your vicinity. The electromagnetic pulse (EMP)
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.
Most data centers cannot resolve the infrequent but potentially catastrophic problems just described
without pulse meters and other special equipment. These problems can cost a great deal of time to
identify and resolve, so take precautions by providing a properly grounded and shielded
environment, with special attention to issues of electrical surge suppression.

Distance Limitations

The length of your networks and the distances between connections depend on the type of signal,
the signal speed, and the transmission media (the type of cabling used to transmit the signals). For
example, standard coax cable has a greater channel capacity than twisted-pair cabling. The distance
and rate limits in these descriptions are the IEEE recommended maximum speeds and distances for
signaling; however, you can usually get good results at speeds and distances far greater than these.
For example, the recommended maximum rate for V.35 is 2 Mbps, but it is commonly used at
4 Mbps without any problems. If you understand the electrical problems that might arise and can
compensate for them, you should get good results with rates and distances greater than those shown
here. However, do so at your own risk. We do not recommend exceeding published maximum data
rates and transmission distances.
The following distance limits are provided as guidelines for planning your network connections
before installation.
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Bad practice can result in radio interference emanating from the plant wiring.
Strong electromagnetic interference, especially as caused by lightning or radio transmitters, can
destroy the signal drivers and receivers in the router, and can even create an electrical hazard by
conducting power surges through lines and into equipment. (Review the safety warnings in the
section "Working with Electricity" in the chapter "Preparing for Installation.")
To predict and remedy strong electromagnetic interference, you may need to consult experts