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Installing the 56/64 kbit data communication
Chapter 5
cables
Installing the terminal
6
Installing the 56/64 kbit data communication
cables
When using galvanic connection between protection terminal and communication equipment or
point to point galvanic connection between two protection terminals it is essential that the cable
installation is carefully done. This is true regardless of type of module used, G.703, V.36, short
range galvanic etc., only the possible length of the cable differs. The factors that must be taken
into account are the susceptibility for noise disturbance, due to that the levels of the communi-
cation signal are very low.
For best result a cable with twisted pairs and double screens should be used, one screen for each
twisted pair and one surrounding all pairs. Each signal shall utilizie its own twisted pair as in
figure
12. The screen for each separate pair shall be connected to internal screen or ground con-
nection of equipment in one and the same end only, if available, or in other case connected to
earth close to the equipment.
The outer screen surrounding all pairs shall be connected to a solid earth at each end close to the
equipment.
Note also that recommendation about cable lengths given for modules according ITU/EIA inter-
face, excluding the short range galvanic module, are under the assumption that the two devices,
the protection terminal and the communication terminal, are within the same building and that
the earthing system of the building is of good quality. It also presumes that the environment is
relatively free from electromagnetic interference.
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