Every guide I read mentions how you can't use PoE supported cable for console port, RJ45 not USB, because you can fry the port but aren't all cat 5e and after cables PoE compatible, and I was always doing that and nothing ever happened.

So is this something like anti-static mat or is it 100% guaranteed point of failure?

And I never met sys admin that cared so am I overthinking?

Thank you

  • 1
    The difference between "PoE" cable and 5e cables is the conductor size and temperature rating of the insulation. Electrically, they are identical. Can you give an example of where you read this?
    – Ron Trunk
    Commented Jun 3, 2022 at 15:05
  • manuals, I have to map out hardware at my new job and I have to connect to everything and in every router and switch manual they say don't use PoE compatible cable you will fry/damage the port Commented Jun 3, 2022 at 16:25
  • 4
    Are you sure they aren't saying, don't connect a console port to a PoE switchport? Cable is cable.
    – Ron Trunk
    Commented Jun 3, 2022 at 16:29
  • Has any answer solved your question? Then please accept it or your question will keep popping up here forever. Please also consider voting for useful answers.
    – Zac67
    Commented Oct 31, 2022 at 19:07
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer.
    – Ron Maupin
    Commented Nov 19, 2022 at 23:00

1 Answer 1


That's nonsense. PoE uses bog standard Cat 5e or Cat 6 cables. If you max out both the cable length allowed for twisted-pair Ethernet (100 m) and power delivery, you just need to make sure that the wire gauge doesn't cause the voltage to sag below the specs. (Packing lengths of parallel cables tightly also requires care to not exceed the temperature ratings.) Accordingly, a special "PoE cable" isn't really a thing.

Also, an IEEE PoE port on a PSE detects whether a powered device (PD) is connected. If there's no PD, there's only negligible voltage on the cable that can't fry anything by design.

The situation is quite different if you encounter non-IEEE or passive "PoE" - connecting that to arbitrary devices can really fry them. You might want to stay clear.

However, PoE ports are Ethernet ports. I wouldn't try to connect them to serial or USB console ports. "RJ45" or rather 8P8C is just the form factor that's often used by other protocols than twisted-pair Ethernet as well.

  • We had some building automation devices that would blow up when connected to Cisco switch interfaces, and we had to disable PoE on any switch interface to which we were going to connect them. It turns out that the way the interfaces on the devices were wired would signal the switch to send power, even though the devices could not handle PoE. Of course, the device manufacturer denied there was anything wrong with the devices. One of our techs tried cutting a trace on the device board of a known good one, and it worked just fine on a PoE interface without disabling power on the interface.
    – Ron Maupin
    Commented Jun 3, 2022 at 18:52
  • If interfaces are designed in a weird way, not according to IEEE specs, that could happen. PoE detects if there's a signature current between cable pairs, which clearly is a severe design flaw for non-PoE devices. Also, since current runs between pairs, their magnetics design must be completely off.
    – Zac67
    Commented Jun 3, 2022 at 18:58
  • Yes. I have not heard about this for a few years, so either the group using the devices is doing something else, or the manufacturer fixed its design.
    – Ron Maupin
    Commented Jun 3, 2022 at 19:00

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