Fiber only in DataCenters?

George Herbert george.herbert at
Fri Dec 21 19:15:10 UTC 2012

On Fri, Dec 21, 2012 at 10:58 AM, Owen DeLong <owen at> wrote:
> On Dec 21, 2012, at 10:54 , George Herbert <george.herbert at> wrote:
>> On Thu, Dec 20, 2012 at 3:20 PM, Matthew Kaufman <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 at

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