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3.2 Cable Installation
Wire type, number of wire pairs and number of individual wires are to be
determined for individual sections of the wiring system according to the
guidelines set down below.
* 4-wire twisted pair cables are to be used for wiring between indoor
terminal boards, intermediate terminal boards, main terminal boards, etc.
* Outdoor wires should be used where wiring passes through inaccessible
areas such as in ceilings or under floors. Indoor wires may also be used,
however, in cases where there is no risk of deterioration due to exposure
to heat, etc.
* The number of cable pairs laid should be determined considering the
possibility of future expansion of the system.
* There is a limit to the diameter of cables that can be used to connect
stations to the terminals of EX-16. This limit must be taken into con-
sideration when planning the wiring of this system. The diameter should
measure between 0.016" (0.41mm) and 0.031" (0.79mm).
3.3 Core Diameter Versus Transmission Distance
The diameter of the cable to be used should be determined so that the set
limits for speech attenuation (3dB maximum for transmission from the
exchange to the station) and for the DC resistance (DC loop resistance: less
than 300 ohms) are met.
Speech Attenuation, DC Loop Resistance and Service
Distance as Functions of Core Diameter
AWG no.
(solid)
22
24
Core
Diameter
mils. (mm)
25.3
(0.64)
20.1
(0.51)
Speech
Attenuation
dB per 1000 ft.
(dB per 1 km)
0.411
(1.35)
0.521
(1.71)
DC Loop
Resistance
per
1000
ft.
per 1 km)
35.1
(115)
54.5
(179)
Service
Distance
ft.
(km)
7,300
(2.2)
5,500
(1.1)
12