Cable termination

ayha1999 used Ask the Experts™
Is there any unused pairs of cables in RJ-45 connection? How may pairs are necessary for using Cisco IP phones?

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CAT5 cable is sufficient for IP phone and most networked devices.  Problems due to faulty cabling are most frustrating to deal with.  Therefore, if you can, replace/install proper cables to save you from future headaches.

If you are in a bind, you can use the "unused" pairs.  RJ45 has 4 pairs (8 strands of wire).  CAT5 uses 2 pairs (pins 1 & 2, 3 & 6).  You can rewire the unused pairs.  

Here is a link to the wiring layout:
Top Expert 2014
To use a Cisco IP Phone you only need TX and RX pairs.  If you want to use PoE to power the phone you need all 4 pairs.
Les MooreSr. Systems Engineer
Top Expert 2008
Also, the newer phones are Gigabit which also uses all 8 wires...
So POE and/or Gigabit uses all 4 pairs always.



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