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

Bruce Griffiths bruce.griffiths at xtra.co.nz
Thu Jan 8 05:14:30 EST 2009


Poul-Henning Kamp wrote:
> 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".
>
>   
Similarly for Quadraxial cable there are 2 interpretations:

1) an inner conductor surrounded by 3 coaxial tubular conductors all
insulated from each other.

2) 2 twisted pairs with an outer tubular shield used in some high speed
network cabling.

Both meanings are in common use.

Quintaxial cable seems only to be mentioned in texts on cable shielding.
In which it consists of a central conductor surrounded by 4 coaxial
tubular screens all of which are insulated from each other.

Bruce




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