RE: Cat 5e or Cat 6 -- shielded or unshielded?

["Keith Doxey" <ukha@xxxxxxx>]

> -----Original Message-----
> From: Nick Shore [mailto:nick.shore@xxxxxxx]
> >
> > I am running 2 RJ45 sockets in each room down to a wiring frame
in
> > the basement.  My question therefore is:
> >
>
> Personally, I would increase the number of sockets to at
> least 4 per room,
>
> > To Cat5e or to Cat6... that is the question.
> >
>
> Cat5e - no real need for cat6 AFAIK
>
>
> > Whether tis nobler to use shielded cable or unshielded cable when
> > running through walls which could be near electricity...
> >
>
> Unshielded is easier to run and terminate, and cheaper too,
> cross mains cables at 90 degrees, though
> I'm sure that Mr Doxey will be along in a minute to explain
> the features of twisted pair, and its inherent anti-interference
properties.
>

Am I really that predictable :-)

1. As Nick has said, RUN MORE SOCKETS. Everyone on this list who though
"two
sockets will be enough" has or will eventually come to regret that
decision.

2. CAT5e vs CAT6. I see no need for anything better than CAT5e as Gigabit
ethernet will run fine over that if properly installed. Cable should not be
subjected to excessive pulling forces during installation, should not be
bent round too tight a radius, and should not be subjected to crushing
including people putting there muddy boots on it whilst laid out on the
floor prior to installation. Termination should be done with the correct
tools and the pairs should not be untwisted for more than is absolutely
neccessary to terminate on the punchdown.

3. Unsheilded vs Shielded. Run Unshielded. It your house has a source of
interference great enough to warrant the use of Sheilded CATx cable you
have
a serious interference problem somewhere which will cause grief with other
equipment as well. Unless installed correctly using the proper connectors
and tools, shielded cable can actually make matters worse. As Rob pointed
out, the shield should only ever be grounded at one end otherwise a ground
loop will be formed which can lead to currents flowing via the shield.

Another undesireable effect of using SHIELDED cable is that the screen add
to the capacitance of the cable. The greater the capacitance, the greater
the losses at higher freqencies which is precisely what you want to avoid
in
the quest for maximim speed.


The whole point of CAT5 being twisted pair is that it intended for the
distribution of BALANCED aka DIFFERENTIAL SIGNALS. These consist of two
signals of Equal but Opposite polarity. At the receiving end the DIFFERENCE
is taken as the active signal. Any interference picked up by the cable will
of equal strength AND Polarity therefore the Difference between the two
interference signals will be ZERO hence the interference does not exist.

With regard to mains crossing and separation. There should ALWAYS be a
physical barrier eg trunking or at least a 50mm separation between low
voltage and mains voltage circuits. Best practice is to keep them as far
away as possible particularly when running parallel for long distances but
one fact often overlooked it that a mains cable is also
"balanced". In most
cases the current flowing down the live is the same as the current flowing
back along the neutral and these are flowing in opposite directions
therefore any interference in that cable effectively cancels out. For
anyone
who doesnt believe this, get a "Clip On Ammeter" and put it
around a normal
mains cable. The reading will be zero or very close, to get a proper
reading
it needs to be cliped around a single conductor due to the cancelling
effect
of the wire carrying the return current.

Hope that helps

Keith

www.diyha.co.uk
www.kat5.tv