Fiber only in DataCenters?

Owen DeLong owen at delong.com
Fri Dec 21 18:58:28 UTC 2012


On Dec 21, 2012, at 10:54 , George Herbert <george.herbert at gmail.com> wrote:

> On Thu, Dec 20, 2012 at 3:20 PM, Matthew Kaufman <matthew at 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




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