unused pins in cat5

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 Question by Joe rup posted 04 Apr 2004
 unused pins in cat5
I wanted to know what are the unused pins 4,5,7,8 used for? I would like to know if I could disconect the unused pins from being crimped into the rj45 connector and hook a voice line through it. I figure that I could use the brown&brown white to connect an anolog phone line. Is this parctical and even reliable to the data transmition quality on the same cable?
 Answer by Joseph Golan posted 05 Apr 2004
Dear Joe,

It is not advisable to do what you are suggesting for a few reasons.

1. Down the road you may end up using one of the protocols that require all 4 pairs like 1000BaseT.
2. Sharing a sheath with multiple services may cause unwanted crosstalk on signals. The analog line you are looking to add has a nominal voltage of 48VDC and a ringing signal of 90-105 VAC @ 20-30 htz. This ringing signal can cause interference with the data on the other pairs.

Save yourself the problems later and run a separate cable for your voice line.

Joseph Golan, RCDD

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