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I'm not interested in PoE, I don't need data transmission in this project

I'm interested only in the wires inside an ethernet cable

I want to wire several devices (ESP nodes) all over my house. I can't use batteries on all nodes, and since I've decided on a central power supply, I'll connect all notes on the supply.

My original idea is to have a power unit (24v 100W or more) in the center of the house and from the power unit, ethernet cables will send 24v to each room in the house. On each room there will be a step down converter to turn 24v to 3v, 5v or 12v, as the local nodes require.

  1. Can I use the 4 pairs on the ethernet cable to supply power?
  2. Can I use 6 wires to vcc and 2 to ground?
  3. Can I supply different voltages on the same cable?
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  • \$\begingroup\$ PoE has nothing to do with data transmission \$\endgroup\$
    – jsotola
    Jun 24 '20 at 14:56
  • \$\begingroup\$ @jsotola I know, but I want to build my power distribution without a PoE device and people seem to be quite fond of PoE devices \$\endgroup\$ Jun 24 '20 at 15:13
  • \$\begingroup\$ off-the-shelf functionality, easy to run lan cable if not already installed, no need for AC power at device location ... what's there not to love \$\endgroup\$
    – jsotola
    Jun 24 '20 at 15:47
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Can I use the 4 pairs on the ethernet cable to supply power?

Sure. They're just wires.

Can I use 6 wires to vcc and 2 to ground?

Sure. They're just wires.

Can I supply different voltages on the same cable?

Sure. They're just wires (and you have 8 of them). For DC power purposes, the twisting doesn't really make a difference.

Things to note:

  • If you're planning to use more than about 1 amp per wire, make sure to find out what size of wires you have, so you can look up the resistance and maximum current. See here: Current over CAT6 ethernet cable

  • If you have a single centralized power source, then it may be a good idea to put a separate fuse on each power wire (at the end with the power source). Not ground wires.

  • If you do this, you obviously can't use the same wires for Ethernet. 100Mbps Ethernet only needs 4 wires though, so you can use the other 4 for power.

  • There is a standard system for this called PoE (Power over Ethernet). With PoE, you can use the same wires for Ethernet. This uses 48V and can transmit up to 60W of power on each cable (but it also depends on the power source and receiver). If you decide to use PoE, you can use standard equipment instead of building your own. Devices which send PoE power are called PoE injectors and devices which receive the power are called PoE splitters.

  • If you use normal Ethernet connectors (i.e. RJ45 connectors) then some moron will come along and plug in an Ethernet device, which is a short circuit. You should be prepared for that to happen. Maybe you can use different connectors or at least use big red warning labels. (thanks to awjlogan in comments)

If you are planning to install these permanently, you also need to check what your building code says about low-voltage wiring. There may be additional requirements, such as keeping the low-voltage wiring separated from the mains wiring.

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  • \$\begingroup\$ Thanks, that was very insightful. The project is mainly ESP and Arduinos, so I don't need (and want) the data over ethernet \$\endgroup\$ Jun 24 '20 at 14:58
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    \$\begingroup\$ As another caveat: do not use RJ-45 connectors on the end, guaranteed to be plugged into an actual network device. \$\endgroup\$
    – awjlogan
    Jun 24 '20 at 14:58
  • \$\begingroup\$ Since the step down converter takes a small current and high voltage to small voltage and high current and I'm going to use primarily 5v, would a laptop power supply be enough? rated at 48v 0.35A \$\endgroup\$ Jun 24 '20 at 14:59
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    \$\begingroup\$ @NicosKaralis Logan is saying: if you use normal Ethernet connectors then some moron will plug them into an Ethernet device, which is a short circuit. \$\endgroup\$
    – user253751
    Jun 24 '20 at 15:05
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    \$\begingroup\$ @NicosKaralis - user is correct. It's always a bad idea to use a standard connector for a non-standard purpose, doubly so if you're putting power down it. Oh, and not just morons, very easy to do if you're rummaging around for the right cable :) \$\endgroup\$
    – awjlogan
    Jun 24 '20 at 15:20

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