[time-nuts] Standards sought for immunity of shielded cable links to power-frequency ground loops

Poul-Henning Kamp phk at phk.freebsd.dk
Thu Jan 8 03:47:29 EST 2009


In message <OF3277AC5A.F5D1FAE8-ON85257537.008059CF-85257537.00817C56 at mck.us.ra
y.com>, Joseph M Gwinn writes:

>> That's technically speaking not triax, that's double shield.  Triax
>> would have the conductors and one shield.
>
>No, I think that's twinax: <http://en.wikipedia.org/wiki/Twinax_cable>. 
>
>Triax is a center plus two concentric shields: 
><http://en.wikipedia.org/wiki/Triaxial_cable>.

Sorry, I fumbled what I wrote there.  I would say wiki is wrong
here, the usage I am used to is:
	coax: single conductor + shield
	twinax: twisted pair + shield
	triax: the wires + shield
	
>> (Who once lost all ethernet interfaces, the access control system
>> and a few minor computers when a moron first created and then cut
>> a 600+ A ground loop).
>
>Was there a big bang?  What was the source of the 600 amps?

They replaced the separation transformer with a UPS, and they
connected the two sides ground together at the UPS.

Unfortunately the grounding on our secondary side was much better
than the power companys grounding on the primary side, which was the
entire point of having the the transformer in the first place.

Yes, there were a significant bang and his two-hand wire-cutter was
recategorized from "tool" to "industrial art".

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.




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