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?
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 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.

Sincerely,
Joseph Golan, RCDD

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