Max Cat5 Lenth with PoE

Posted on 2006-04-19
Last Modified: 2013-11-09

The max length of Cat5 Cable on a Fast ethernet network 100baseT is 100m

I have a PoE injector wich will support 100m.

Will it be possible to have 100m from a router to the PoE injector, and then another 100m from the PoE injector to the Access Point?

If ithis is NOT possible, please answer the following question:

ROUTER -->(1. max lenth of cable) --> PoE Injector --> (2. Max lenth of cable) --> AP


Thank  you
Question by:Beeshoring
    LVL 1

    Expert Comment

    If your PoE injector is rated for 100m then your setup should work just fine!
    LVL 12

    Accepted Solution

    If the PoE injector operates as a switch, it is possible to go 100m per section.

    If it does not, your aggregate length limit is 100m.  The received signal at each end would be too weak to distinguish at 200m.
    LVL 1

    Assisted Solution

    chances are the injector even if rated for 100m will do nothing more than jumper the 48v onto one of the pairs where is is connected.

    the 100m is probably the max distance before the power signal starts to suffer from attenution & crosstalk.

    as a general rule of thumb, cat5 runs should be a short as possible
    a second rule of thumb is that POE cat5 cables should be even shorter!!!!

    if you need a run that is 100m long, i would run a 99m cat5 cable from my switch, and then connect the POE injector 1m from the device.

    basicly keep the powered section of the run as short as possible.

    of course if this was for some low demand device like cctv cameras, or even 802.11b wifi access points, i might consider dropping the speed of the link down to 10mb, which would allow you to 'get away' with a much longer cable run - not technically perfect, but still very effective when needs must!

    LVL 3

    Author Comment

    Thanks for the tips!!!

    Well at first I had just less than 100m to the Poe injector and then about 70m to the AP. I could not get an IP, so I put a switch just before the PoE.

    Router -100m-> Switch -0.5m-> poe injectore -70m-> AP

    I then worked and I received an IP. It is a bit up and down, one moment it's excellent and the next moment the SSID is not even there,  so still need to track down that problem.


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