On Wed, 17 Jul 2013 18:08:49 +0100, RJH wrote:

On 07/06/2013 22:02, tony sayer wrote:
In article om, mick
scribeth thus
On Tue, 04 Jun 2013 20:40:24 -0700, Roy Brophy wrote:

I am running a Cat 5 cable close to a 6mm SWA cable over a 15M run.

Is it worth using shielded Cat 5?

It's supplying a garden studio so there will be the occasional
electric fire / kettle kicking in and out.

Roy


At 15m and if trenching allowed, I'd just bury some hosepipe a minimum
of 12" (preferably 24") away from the armoured & thread cat6 through
it. The pipe lets you pull another through if you need to (include a
draw wire!). You should be able to use gigabit ethernet over that -
something that wifi can only dream about. It's simpler and cheaper
than fibre. OTOH, if you can't allow that sort of spacing, then fibre
is really the only answer.


Why would you need to be 2 foot away from a cable thats very
effectively shielded?.

CAT 5 is a very good balanced transmission system and is inherently
good at rejecting other electric fields, so why so far away?..


I'm running some cat6 alongside mains cable in places - obviously, it's
the easiest route to follow through a house. I did read that it's not
advisable, but thought I'd give it a try and so far, so good. Do you
think that ethernet-next-to-mains-equals-disaster is an urban myth?


By the way, SWA isn't a very good screen at networking frequencies. It's
better not to depend on it.

As for cat5 being balanced, look at it this way: both wires in the pair
are being moved up and down in voltage at 50Hz by mains hum. Data is
carried in the difference between the voltage on the pairs. At some point
the 1s and 0s become 1s and 1s, as the hum voltage overcomes the
differential voltage at the top and bottom ends of the 50Hz waveform.
That's when your network dies.

You can get screened cat5, which helps with the hum problem a lot, but it
also slows down the network due to capacitance to earth. Don't use it on
long runs. Better to avoid running close to mains wiring for more than
about 3m.