Is it possible to use a UTP cable for:
- 12V DC (~30W),
- 100BASE-TX Ethernet, and
- A single phone line,
at the same time? 100BASE-TX should give me two spare pairs, can I use one pair for the phone line and one for the power?
My plan is to supply a (rather old) VoIP-capable board with power, internet and a hook it up to a single phone. Can I do all that with a single cable? If yes, how do I do the wiring (i.e. which are the spare pairs in 100BASE-TX Nevermind. Found that on Wikipedia)?
To clarify, I would only run this over a short distance, 1-2m.
Best Answer
IEEE 802.3af POE has two modes, mode A sends power on the "data pairs" while mode B sends power on the "spare pairs". However that is not very relevant as it doesn't sound like you are planning to use that. It sounds more like you are planning a "Ghetto POE" type setup.
I wouldn't worry too much about mixing POTs and Ethernet on the same cable, especially if the POTs link is only local. I also wouldn't worry about CAT5 vs CAT5E on a link this short.
The bigger problem would be current on the DC power lines. 35W at 12V is nearly 3A. Apparently the safe current limit on the conductors is 350ma so if you used one conductor for power and one for ground you would be running nearly 8 times the acceptable current on each conductor. Even if you used the whole cable for power and ground you would still be running at over double the acceptable current.