[c-nsp] Galvanic isolation for Ethernet?

[Victor Sudakov]

Michael Loftis wrote:
> No standard surge protector will help at all for you I'm betting.  

I have already guessed that therefore I was asking for something
better than standard :-)

> As
> some have mentioned you're probably suffering significant (if
> intermittent) common mode voltages...ethernet ports are already
> "galvanically isolated" in the switch itself, and usually in the
> device too, there's a transformer that'll remove the common mode
> voltage component from the signal.  

Last time I looked at a NIC (and the inside of a toasted Catalyst) I
don't remember seeing any transformers. But probably I did not look
well enough, or they do not look as a typical transformer. Do you care
to show a picture please?

> If you've enough common mode
> voltage to fault those out you may still be well short of "surge"
> voltages that are protected by most equipment.  You might improve the
> issue by re-terminating each end only leaving the "spare" copper pairs
> connected at one end of the RJ-45 (the switch end
> generally)...

Sounds like magic but could you elaborate? I did not quite catch the
picture.

> ultimately I've found nothing cures these issues except
> full optical isolation (using a media converter at each end of the
> building to building runs...in some cases this meant colocating
> another switch in each building) and not running copper between the
> buildings.

Well, there are different rugged industrial copper Ethernet solutions
for outdoor use (e.g. from Siemens), what do they use?

> 
> The root cause is almost always bad grounding in one building or
> another.  In a couple cases we discovered that ants and termites had
> colonized around the grounding rod.  In another we discovered the

Our electricians say that the grounding is correct, all grounding
circuits on the site are interconnected and that they measure the
parameters annually.  I am not the person to expose them to be lying
(if they really are), I lack such qualification.


-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
sip:sudakov at sibptus.tomsk.ru