[Tfug] Switches -- and hubs!

[Bexley Hall]

Hi Adrian,

--- On Thu, 12/24/09, Choprboy <choprboy at dakotacom.net> wrote:

> During the development of ethernet at Xerox PARC it was
> noted that there was a 90V ground differential between the 
> two ends of the building the first ethernet cable spanned.

Yikes!

> Ethernet is an isolated transmission medium, so it 
> can tolerate a large differential. I don;t like to do it..

Subject only to the degree of isolation the transformers
can provide (assuming this to be the path of leeast
resistance and not some *other* "air gap" from a bad PCB
layout  :<  )

> but sometimes you have to use copper. In those cases you can get 
> telcom grounding blocks fairly cheaply for each end. Throw in a
> 60V or 90V cutoff arrester on either end and 
> you can protect against most but really close/direct
> strike.

I don't like "antennae".  Tempting lightning to strike nearby is
just asking for a problem that could otherwise be avoided.

I've had two direct/near direct strikes in my lifetime.
One, a walnut tree 12 feet from the house (30 feet from
the TV aerial).  Aside from peeling the bark off one side
of the tree for its full 60-70 ft length and shaking the 
house, no real damage.

The other was *presumably* a nearby strike (different location)
as I didn't find any direct evidence of contact with the house.
Toasted the protection zeners in a couple of electronic phones
(amusing sensation when you lose telephone service -- since you
are more often experiencing POWER losses!) and "magnetized"
the TV.  (took a month of on/off cycles to degauss the set
to the point where color purity was restored).

Nowadays, I wonder what other things would have been damaged
in such strikes...