There is an Ethernet cable that runs from a server room to an office. That cable is connected to a router. There are times when we need to reset that router and I will like to do that remotely. There is only one Ethernet cable that runs to the office I wish there was one more.

I will like to place an arduino or raspberry pi at the office that will be responsible for turning off and on the router with a relay.

I need to send a signal from the server room to the arduino located at the office.

I have tried using the NRFL01 and other radio signals but the distance is to far and the signal is lost because there is a lot of walls in between.

I want to use 2 of the existing Ethernet cables just like a Poe switch uses some off the wires to inject power. Instead of injecting power I will like to insert a signal. What cables can I use of the internet cable. I know very little about networking. Does it matter if it's a cat5/cat6? Can I do something like that?

  • \$\begingroup\$ You say there is only one ethernet cable running to the office, but later say you would like to use two of the existing ones. Are you perhaps confusing wires and cables? \$\endgroup\$
    – JYelton
    May 26, 2020 at 22:55

1 Answer 1


If it is a CAT5 or CAT6 twisted pair cable, and it's used by 10baseT or 100baseT Ethernet (max 100 Mbit Ethernet), then the existing connection is only using pins 1,2,3 and 6 (usually the green and orange pairs) of the RJ45 plug. You can use the other 2 pairs (brown and blue, on the remaining 4 pins) as you like, even for a complete second Ethernet line, although they will interfere with each other (which, depending on the shielding, the speed and the length, may or may not make a difference.

There are probably better solutions for your application (like TCP/IP controlled relays), but this answers your question.

  • 1
    \$\begingroup\$ Good advice on TCP/IP relay. It is funny that the very first relay I googled has this in the description: "Can be used in smart home control, control router to restart when network is off" \$\endgroup\$
    – Maple
    May 26, 2020 at 20:43
  • \$\begingroup\$ I will not be able to use a tcp/ip relay because if the switch goes down then I will not be able to comunícate with the tcp/ip relay. I will have to buy that and another tiny switch. Thanks for the help it was helpful! \$\endgroup\$
    – Tono Nam
    May 27, 2020 at 4:34
  • \$\begingroup\$ Most people like to run 1000Mbps ethernet which uses all 4 pairs though. Perhaps you could add a low-frequency signal like how PoE works. \$\endgroup\$
    – user253751
    Jul 3, 2020 at 10:15

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