[rescue] Anyone here familiar with 10Base36 ?!?

[Greg A. Woods]

[ On Saturday, September 21, 2002 at 14:57:29 (-0400), Dave McGuire wrote: ]
> Subject: Re: [rescue] Anyone here familiar with 10Base36 ?!?
>
> On Saturday, September 21, 2002, at 02:50 PM, Greg A. Woods wrote:
> > Except that most fibre cable for outdoor use has a metal jacket....  
> > :-)
> 
>    I use "ordinary" fiber and put it in a liqui-tite conduit or 
> something similar.

That's a good idea -- though I don't know about going several kilometers
that way.....

> > Make sure it's properly grounded!
> 
>    ...and only at one end.

No, that would in fact be dangerous!  The rules for grounding outside
cable plants, especially aerial ones, are very much different.

The sheath must be properly grounded directly to a really good earth
ground at both ends (and sometimes also at any point where it is joined
or tapped).  That way if it gets cut one segment that's still physically
(but perhaps not electrically) attached to equipment where you might
touch it or where lightning could jump to unprotected equipment won't
ever be left ungrounded.  Ideally cable sheaths should be grounded at
the point where they enter a building, and of course cable entry points
must be properly chosen too.

Paraphrasing from some other summary documents available online:

The NEC requires a listed primary protector at both ends whenever an
aerial communications cable is routed across a street and whenever
aerial or underground circuits may be exposed to accidental contact with
power conductors operating at over 300 volts, or to lightning or "other
transients".  A cable is also considered to be "electrically exposed" if
any of its branches or individual circuits is exposed to such contact or
transients.

A lightning exposure guideline is included in the NEC Section 800-30(a).
It states that inter-building circuits are considered to have an
exposure to lightning unless cable runs are 140 feet or less, buried
with a properly grounded shield.  The NEC also states that the shield
must be bonded to the building's ground electrode system at each end.

Requirements for building ground systems are also explicitly documented
in the NEC.

See also CSA-T527 and TIA/EIA-607.

The "only at one end" rule only applies to sheaths of signal
transmission lines within a building, and only when it is protected by
other means from any accidental contact with high-tension power
conductors, and usually is only necessary to apply where you can't
guarantee that the chassis' of the equipment at either end are properly
bonded to the same single-point ground system.  In those cases the end
that's grounded really should be the one that's permanently connected
(eg. the host system, or patch panel, or whatever).

-- 
								Greg A. Woods

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