fast ethernet limits

Tue Jan 14 00:01:22 UTC 2003

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- --On Monday, January 13, 2003 13:35:14 -0500 blitz <blitz at macronet.net>
wrote:

> I find the same Kevin..I've done a lot of work in broadcast stations as
> well, and ground loops are a constant problem. Hum is introduced into
> audio lines, even in balanced pairs, and Cat5 is not much different.

Read the articles at www.compliance-club.com -- there is a two-piece
article on audio systems, by the technical manager at Cadac. It definitely
goes against all gut reactions we've forced ourselves into; especially in
the telco/audio business. 

But it makes sense! It works! And, usually the audio folks were the last to
find out: Look at your average network component; the grounding scheme of a
big modern router. It is mesh grounds all over the place -- and because it
is the only way it will ever get the box approved by FCC/UL/CSA or any
similar agency. 

> In a high rise, I can see a neutral failing somewhere on a high floor,
> and that piece of #10 going incandescent, setting fire to anything
> combustible between the floor its terminated on and earth ground. (The
> resistance of an old steel framed building is NOT always lower than that
> piece of copper, especially old riveted buildings).

Which is why one must construct a low-resistance/impedance mesh, connecting
shields and grounds all over the place, so as to short out the potentials.
The steel frame could serve as one of these grids, but probably needs to be
augmented. And, I wrote "AWG way below 10"... If it is not enough, get a
thicker one, and get a new electrical contractor. (see below) 

> Maybe they do it differently in the EU, but fire safety is also a concern
> to me.

If you have potential differences like these the house needs a new
electrical grid. Wait, that means that the entire North American continent
needs rewiring ;-) Anyway, the mains PE MUST be made the best path home,
and in a fail-safe manner. 

> Thank you, but I'll ground nearest to the earth, common bonded point. Its
> served me well over the years.

Look at the emissions that manage to get into a star grounded, one point
only system vs emissions bounced off a mesh grounded system with a decent
EMC testing rig and repeat that phrase afterwards ;-)

- -- 
Måns Nilsson            Systems Specialist
+46 70 681 7204         KTHNOC  MN1334-RIPE

We're sysadmins. To us, data is a protocol-overhead.
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