Site Wiring Guidelines
Cisco 12008 Gigabit Switch Router Installation and Configuration Guide
2-20
EMI Considerations
When wires are run for any significant distance in an electromagnetic field, interference can
occur between the electromagnetic field and the signals on the wires. Be aware of the
following points:
•Bad site wiring practices can result in the emanation of radio frequency interference
(RFI) within the site.
•Strong EMI, especially that caused by lightning or radio transmitters, can destroy the
signal drivers and receivers in the router. EMI can 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 an RFI expert.
If you use twisted-pair cables in your plant wiring with an adequate distribution of
grounding conductors, the plant wiring is unlikely to emit RFI. If you exceed the
recommended cabling 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 hav e had p roblem s
of this kind in the past, you may want to ask experts for assistance in electrical surge
suppression and shielding.
Most data centers cannot resolve the infrequent, but potentially catastrophic, problems
described above without pulse meters and other special equipment. Such problems are
difficult to identify and resolve, so take precautions by providing a properly grounded and
shielded environment, paying special attention to issues regarding electrical surge
suppression.