90-100Volts in CAT5 cable???

[Evildead666]

Hi,

I have a Gigabit network at home, and have been getting a 'buzz' from touching the shielding of my network cable, everytime i plug-unplug it. I measured it with a multimeter, and came up with 90 to 100V . Explains the buzz...

I also have this problem at work on a simple 100Mbps network.

Does anyone know why this is, and if its a problem with my network somewhere?

Cheers,

Jez

[dZeus]

ehm, isn't the shield of the cable connected to the ground of each pheripheal that it's connected to? maybe you're in fact measuring the potential difference between your pc case and the ground (try to check potential difference with the multimeter between your pc case and a central heating radiator or waterpipe).

[Evildead666]

The Computer case doesn't have any voltage. i measured the + on the case and the shielding, and the - on the ground of a wall socket. I get a buzz from just holding the cable between my fingers, and not touching anything else. The multimeter only came up with 90-100V when the + was on the CAT5 shielding...edit: while it was unplugged. the hub is grounded, and i get a voltage from all the cables from the switch, and a 100Mbps hub, connected to the other hub.

edited twice for comprehension.

[gt40]

um, cat5 cable is not shielded (do you just mean the plastic jacket)
what you might be reading is voltage induced in the cable by being close to an AC source (light, transformer, etc).

[dZeus]

Cat5 usually is UTP but I've seen STP CAT-5 as well.

[Jon P. Inghram]

I don't know how French electrical wiring is set up, but if it's anything like the US the neutral and ground should be at the same potental, while the hot line is at it's specified voltage relative to both neutral and ground assuming everything is working properly.

If the house wiring on all circuits is fine (just because two sockets are 5 feet apart on the same wall doesn't mean they're on the same circuit,) I'd disconnect everything (including all external conductors like cable modem/tv lines/telephone lines) and check each device by itself.

[Evildead666]

In the work example, the cable goes from a Peabird 100MBps hub to a computer. There are 2 other cables on the hub, which don't have any sheilding around the socket, so no (detected) problem.
The cable is not looped up, its just long enough to get to the machines.

I thought of induction, but didn't think that a potential difference of nearly 100V could be produced. its not a peak, its constant. I can hold it for more than a few seconds, and haven't seen it drop over time...the hubs have 15V power supplies on them.

[Greebe]

The buildings electrical wiring is either bad or one of the PS's transformers is leaking.

[Evildead666]

I'm unplugging everything, and testing each hub with a multimeter.

@Greebe, even so, how can 100V be generated, if it was the transformer, surely the hub would die.

I would also like to point out that the network is running fine, all the while, the only problem is the annoying electrocution when plugging/unplugging, and when the shielding hits the case, and sparks fly...

Multimeter ahoy, will post results in a bit, cheers.

[Greebe]

This can occur when the neutral (common) AC line had either burnt in two or otherwise became open. What you have is refered to as a ground loop. Have seen it disrupt proper operation of all kinds of electrical equipment in various industrial, commercial and residential buildings.