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Cisco 7204 Installation and Configuration Guide
OL-5101-02
Chapter2 Preparing for Installation Site Requirements
Interference Considerations
When wires are run for any significant distance in an el ect ro mag net ic field, int e rfer en ce ca n oc cur
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 tra nsmitt ers, can d estroy the si gn al
drivers and receivers in the Cisco 7204, and can even create an electrical ha zar d by con duct ing
power surges through lines and into equipment. (Review the safety warnings in the section “Safety
with Electricity” section on page2- 3”.)
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 conducto rs, the
plant wiring is unlikely to emit radio interference. If y ou exceed t he r e co mmend ed dist a nces, u se a
high-quality twisted-pair cable with one ground conductor for each data signal when applicable.
Warning
A readily accessible two-poled disconnect device must be incorporated in the fixed wiring.
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 caus ed by lightni ng 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.
Distance Limitations and Interface Specifications
The size 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 coaxial cable has a greater channel capacity than twisted-pair cabling. The distance and rate
limits in the following 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 c omm only use d at 4 Mbps
without any problems. If you understand the electrical problems that might arise and can compensa te for
them, you should get good results with rates and distances gre ater tha n those shown her e; however, do
so at your own risk.
Note We recommend that you do not exceed specified transmission rate and distance limits.
When preparing your site for network connections to the Cisco 7204, you must consider a number of
factors related to each type of interface:
•The type of cabling required for each type (fiber, thick or thin coaxial, shielded twisted-pair, or
unshielded twisted-pair cabling)
•Distance limitations for each signal type
•The specific cables you need to connect each interface