Re: Fiber only in DataCenters?

[George Herbert <george.herbert () gmail com>]

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