On Fri, Dec 21, 2012 at 10:58 AM, Owen DeLong <o...@delong.com> wrote: > > On Dec 21, 2012, at 10:54 , George Herbert <george.herb...@gmail.com> wrote: > >> On Thu, Dec 20, 2012 at 3:20 PM, Matthew Kaufman <matt...@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.herb...@gmail.com
