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