On Fri, Dec 21, 2012 at 10:58 AM, Owen DeLong <owen@delong.com> wrote:
On Dec 21, 2012, at 10:54 , George Herbert <george.herbert@gmail.com> wrote:
On Thu, Dec 20, 2012 at 3:20 PM, Matthew Kaufman <matthew@matthew.at> wrote:
On 12/17/2012 9:22 AM, joel jaeggli wrote:
If the facility is big enough the utility of twisted pair becomes quite limited, both due to distance and differing electrical potential, multibuilding campuses in particular make this is a nonstarter.
For twisted-pair Ethernet: Distance yes. Differing electrical potential no. It is a balanced pair, transformer coupled at both ends. As long as AC common-mode pickup doesn't saturate the transformer core, it just works.
...Up to certain limits of DC / ground differential between the ends, at which one can cause sparks anyways.
Yes, the POTS telcos use 48V in the same or lower quality wire pairs, and the various CatN wires should be able to take it, and the connectors. I'm not sure whether the sparks were from 110 or 220 V of differential, but I saw sparks.
Sparks come from voltage, but wire tolerance is entirely a matter of amperage.
A 24ga cat-6 wire can take millions of volts as long as you keep the amperage low enough.
Owen
In the ultimate limit, Insulator breakdown voltage is measured in V/mm, but in this case it was almost certainly not that, and merely a case of excessive amps at sufficient volts to give a nice large watts. The subsequent facility power get-well was not cheap. I have also, independently, melted and partly vaporized multiple cubic centimeters of 8 ga wire with a (purely accidental, I assure you) short of 12 volts from a serial stack of D-cell sized NiCd rechargeable batteries. The same works well with an old car 12 V battery and any conductor up to wrenches (not recommended at home...). What's the old saying? Volts hurt, Amps kill? -- -george william herbert george.herbert@gmail.com