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Samit (Electrical) (OP)
11 Jul 01 8:47
Hi!
  I would like to know in detail about the impact of low insulation resistance in the Copper transmission line on the telecommunication network. What would be probable impoact on the signal if the Cu cable in the network ie. between the subscriber and the exchange has low insulation resistance( 150Mohms-km to 1.3Gohms -km)?

 -
Samit
MS2 (Electrical)
14 Nov 02 22:06
As far as voice is concearned,when only a single pair is in play, only when insulation resistance reaches 100k or less will it be noticeable. If there are more than one pair in the same cable, and several pairs share the same low insulation characteristics, crosses will develop and crosstalk will become evident. The lower the insulation resistance the higher the crosstalk. Voltage will appear on idle pairs as a spill-over from active pairs. Also, as is most often the case with telecommunication cables, the outer sheath of the cable will be metalic and it is therefore common to have some conductivity to ground (the sheath is grounded) when low insulation situations occur.
     As far as data is concearned, lets say ADSL running at 1Mb. Low insulation will have a tremendous effect. Anything less than a perfect pair will not allow maximum transmission rate. Usually, anything above 30 Meg ohms is considered perfect (with no ground conductivity). However, there are many more factors, other than pair insulation that affect transmission rate.
150M ohms to 1.3 G ohms would almost be considered an open pair and is very rarely encountered in the field.

 
SparkyDude (Electrical)
15 Nov 02 15:29
The insulation resistance is one of the major factors embeded into attenuation of each transmission line. Attenuation is measured by dB(Decible). There are some requirements for maximum acceptable dB/km for each transmission line.

You may check BICSI's manual and TIA/EIA standards to learn more about this.

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