[Asterisk-Users] OT: VoIP over bonded link

[Andrew Kohlsmith]

On Thursday 23 February 2006 13:57, Bob Goddard wrote:
> It's stupid. Don't ever connect 2 different building with copper.
> Just wait until you get some kind of lightening hit or electrical
> fault, but make sure you are no where near it. Use fibre.

That's a great rule of thumb, but the reality isn't quite so black and white.

A direct lightning strike is not going to draw *any* significant current 
through the ethernet cable, as the moment you try to pull significant 
current, those cables will either open up or vaporize due to IR losses in 
such small gage wire.  You'll have far more current draw through the (I'm 
assuming) metal conduit, which is already grounded.

Yes, you may introduce grounding loops and these will cause other (sometimes 
significant) issues but they have all been solved before.  The best solution 
is to simply take a pair of media converters with a fiber patch cable between 
them, space them out adequately and hope for the best.  You're already going 
to have a conduction path through the power supplies of the media converters 
but with an isolation transformer and appropriate surge arrestors it's about 
as best as you are going to be able to do.

Electrical faults are *easily* dealt with with appropriate fusing, surge 
arrestors, isolation and plain old common sense.

I work in the power electronics industry; we regularly deal with lightning 
strikes (both direct and "close call" style) and while there is very little 
to protect you from a direct strike (we use station-class arrestors) there is 
a LOT you can do to minimize grounding or loop problems when wiring between 
buildings.  Sometimes fiber just doesn't cut it, so no, it's "not just 
stupid."

-A.