[Tfug] Switches -- and hubs!

[Bexley Hall]

Hi Louis,

Yappy Hew Near!

> The location is in Northern California near the coast. 
> Unlike Tucson, Lightning is rarely an issue.  Base-T
> Ethernet does have isolating transformers at both ends of
> the run, so ground loops are not an issue.   Lighting can

Yes.  Though you still have to worry about common mode
voltages.  Note that this also applies to the DC-DC
converters in your PoE devices...

> be a major problem.  Building R5 or R7 at Pima West Campus
> was struck by lightning once.  It was an aluminum structure
> -- quite conductive and well grounded.  We still ended up
> with $27,000 in damage. 

<grin>  Yup.  I recall working on some test equipment for a
three-letter client... their safety department insisted there
be no more than *1* ohm resistance to ground anywhere on the
device.  As if this somehow made it *safe* for people to use!

Open jawwed, I asked the safety officer (a friend of mine),
"WTF?!  The damn thing draws over 100A at 440V.  You think
that 1 ohm is going to look like a 'short'?  I think it's
going to look like a *fuse*!!"  ;-)  (figure 100A into 1 ohm
gives you more than enough voltage to overcome *dry* skin
resistance)
 
> The problem with fiber, as almost always, was the
> termination.  How do you get some one 25 miles from a small
> town to put the connectors on the cable.  

Simple!  Live in the LARGE CITY located 25 miles from that
"small town"!  :>

(couldn't buy preterminated lengths?)
 
> ps.  If you have a 90 volt differential, someone
> doesn't know how to use a meter or they forgot to
> connect the cable to ground at least one end.
> 
> When the Shiva (Used in the movie Tron) laser was first
> fired at Lawrence Livermore Labs the ground loop current
> took out all of the DEC LSI-11 computers used to control the
> mirrors.  They then put in fiber <grin>.