User Manual
SUPM1
page 24 of 94© KEYMILE December 2015 EN/LZTBU 372 129/1 RC
94
Functions and Specifications
3.8 Length of Subscriber Lines
Table 24: Length of subscriber lines
Feature Rating or standard
The maximum subscriber (loop) cable length depends on several factors. One important factor is the resistance of the
loop and the connected telephone set. The DC-resistance of the two wires should not exceed 2x1000 Ω including the
telephone set. The telephone set is typically 200 - 600 Ω.
Maximum cable length
@ 0.4 mm wire diameter
@ 0.6 mm wire diameter
@ 0.8 mm wire diameter
@ 1.0 mm wire diameter
5.0 km
11.3 km
19.9 km
31.0 km
The above values are calculated under the assumption that the telephone set has a DC-resistance of 600 Ω.
Before you operate with a maximum line length investigate also
the following criteria:
- Influence of the cable length on the function of the subscriber
set (national standards for telephone sets).
- Cable attenuation for voice transmission and/or
- Metering pulses.
It is highly recommended to use twisted wire pairs in order to
minimize the susceptibility to cross talk and induced voltages.
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