20

I have an UTP cable coming from a router far, far away. The plastic part which keeps it from falling out of the socket was damaged, and I intend to replace it.

Is there any danger of cutting it while only disconnecting it from my part, and not following and disconnecting it on the other end (which is very hard to be accessed) ?

I mean, while I cut it, some of the 8 cables might make contact with each other. If one end is disconnected and the other not, can it cause any problems?

(the simple form of this question is: If I connect the individual cables in an UTP cable with each other while one end is free and the other end is plugged in, can it damage hardware?)

1
  • 3
    If you're very concerned, you can cut each wire in the cable individually.
    – 9000
    May 16 '12 at 16:21
18

It sounds like you'd have the same problem as if you tried to plug a wrong cable in (like a console cable), any reasonable network card should just discard the data as complete crap (which it would need to do anyway if you had a regular short or background noise)

Especially if you're unplugging one side, you're already taking care of the majority of the problem.

(Note that this is still my answer after your edit, I understand what you're asking, I do not think any reasonable hardware should die from this).

2
  • 5
    Aye, it wont, voltages involved are safe. Just dont be plugging the cut end into the mains, or using it to fly a kite.
    – Sirch
    May 16 '12 at 15:53
  • 2
    I did it, it works, and nothing burned down.
    – vsz
    May 16 '12 at 17:42
26

I suppose if the cable has Power over Ethernet on it, that might be an issue that I can't quantify. Cutting it might short the positive and negative wires that are transmitting power together.

44 volts with 350ma is in the "gray area" where I can't tell you if it's a big deal or ignorable.

If you know you're not pumping PoE on it, then you should be just fine. I've looped back data connections before on purpose when I've been feeling mischievous.

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  • 1
    +1 for mentioning a possible danger. Fortunately, I don't have Power over Ethernet.
    – vsz
    May 16 '12 at 16:03
  • 7
    PoE PSE (Poswer Sending Equipment) doesn't send any power over the wire until it's established that there's a PD (Powered Device) at the other end. The PD signals what power it wants by changing the resistance across certain pairs. If you're using a passive power injector, that's a different story, and one more reason to use actual PoE.
    – Chris S
    May 16 '12 at 16:44
  • @ChrisS Excellent point. May 16 '12 at 17:01
  • Additionally, even if the PD has been detected at the other end, 802.3af-2003 mandates short-circuit protection by the means of monitoring of power draw and the shutdown of power if the draw exceeds the threshold over a given period of time.
    – the-wabbit
    Apr 3 '13 at 6:59
8

It shouldn't cause any problems, but i'd still rather strip the cable at the end, and cut wire-by-wire. This is the only part where there is a large possibility of contact between them. You have to even the wires up and strip the cables anyways, and losing a cm of cable shouldn't cause much difference.

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  • +1 for inherently safer method of disabling any jacketed collection of cables. May 16 '12 at 15:59
  • +1 this is how i was taught to cut telephone cable even when you think it isn't connected.
    – jqa
    May 16 '12 at 17:41
  • 1
    If the goal is to crimp the end, then all the wires should be of exactly the same length, otherwise you'd get unnecessary tension in the wires. Kind of hard to achieve when cutting one-by-one.
    – rustyx
    Dec 24 '18 at 9:59
8

The ports on ethernet switches are transformer coupled so they are isolated from the driving circuit. You'll be safe to cut them without any problems.

1
  • As a side note, the transformer is usually called the "magnetics" when referring to an ethernet circuit.
    – mpdonadio
    May 16 '12 at 20:15

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