Typically, a 26 AWG wire is equal to 81.6 ohm/Kft and 24 AWG wire is equal to 51.3 ohm/Kft.
Note
Interference Considerations
When you run cables for any significant distance in an electromagnetic field, interference can occur between
the electromagnetic field and the signals on the cables. This has two implications for the installation of terminal
plant cabling:
• Unshielded plant cabling can emit radio interference.
• Strong electromagnetic interference (EMI), especially as caused by lightning or radio transmitters, can
destroy the EIA/TIA-232 drivers and receivers in the Cisco VG450 Voice Gateway.
If you use twisted-pair cables with a good distribution of grounding conductors in your plant cabling, emitted
radio interference is unlikely.
If you have cables exceeding recommended distances, or if you have cables that pass between buildings, give
special consideration to the effect of lightning strikes or ground loops. If your site has these characteristics,
consult experts in lightning suppression and shielding. The electromagnetic pulse caused by lightning or other
high-energy phenomena can easily couple enough energy into unshielded conductors to destroy electronic
devices.
Most data centers cannot resolve such infrequent, but potentially catastrophic problems without pulse meters
and other special equipment. Take precautions to avoid these problems by providing a properly grounded and
shielded environment and by installing electrical surge suppression.
If you remove any module, you must either install a module in its place or install a cover plate over the opening.
All module openings must be either occupied or covered to prevent electromagnetic interference.
For advice on the prevention of electromagnetic interference, consult experts in radio-frequency interference
(RFI).
Cisco 450 Voice Gateway Hardware Installation Guide
14
Planning Your Installation
Interference Considerations
