Re: Cable Marking and Separation

[Frank Mc Alinden <fmcalind@xxxxxxx>]

Hi Keith

I think it would be a good idea to upload this message to the files area as
this question pops up every so often ..

Frank
----- Original Message -----
From: Keith Doxey
To: ukha_d@xxxxxxx
Sent: Saturday, May 24, 2003 7:10 PM
Subject: RE: [ukha_d]Cable Marking and Separation


Hi Mick,

Long reply follows....

>I have a number of areas where crossing or close running of cables
cannot
be
>avoided due to the constraints of the house construction I have tried
to
>keep it to a minimum but it is still there.

Many people seem to be absolutely paranoid about maintaining a minimum of
12" separation and never running parallel but in my experience this is
totally overkill. I have worked in nightclubs where all cables have been
run
in the same trunking (WHICH SHOULD NEVER BE DONE BUT IT HAPPENS) for long
distances and ordinary screened audio cable has been adjacent to cables
carrying phase controlled lighting (which is one of the worst forms of
interference you could ever wish to to encounter) with no noticable
interference.

That said... FOR SAFETY and to comply with the IEE Regulations, Low Voltage
and Mains should NEVER be run in the same trunking unless there is a
physical barrier between them. Where there is no pyhsical barrier and
separation of at least 50mm should be made. It is good practice to ensure
that where cables cross, they cross at 90 degrees to minimise any possible
pickup.


>How much attention do I need to give to keeping CT100, CAT5, CAT5
Shielded
>and Alarm cables seperate from each other and is it ok to run like
cables
in
>bundles (eg all speaker cables in a bundle)?

Consider the multicompartment trunking used in an office environment. All
CAT5 cables run in one of the outer compartments, mains in the other outer
compartment with all faceplates fitted to the centre compartment. The
distance between the the two cable compartments is only about 5 inches and
they run for long distances without interference.

>Where cables cross/close run is there any benefit to trying to shield
them
>using aluminium foil or something similar?

IME Not required. CAT5 is balanced so interference is picked up by each
wire
of the pair at an equal strength. Because balanced transmission retrieves
the signal by taking the difference between the two wires, a signal of
equal
strength will have zero difference so therefore not exist. Likewise,
signals
radiated by the CAT5 will be equal but opposite so will cancel each other
out.

Although mains cable is not screened or twisted pair, it is still
effectively balanced as what goes up the live must return via the neutral
unless you have some strange routing of cables. Even a wire to a light
switch where there are only live wires will cancel itself out as the
current
to and from the lightswitch is travelling in opposite directions. Very
close
to the cable the EMI field will be strongest as you will be closer to one
wire than the other but as you get further away the EMI is greatly reduced.
As I said, try wherever possible to keep as much separation as possible
because this is good practice but in reallity I have never experienced
problems.


>For some of the alarm circuits to windows I can run CAT5 or alarm
cable, in
>many cases these windows have several openers and I only need one pair
per
>opener so I am thinking of splitting the cable after it gets to the
window.
>Would alarm cable or CAT5 stand up best to this treatment? I know it
won't
>be CAT 5 spec after I split it but I don't intend installing PCs in my
>windows;)


If there is any movement of the cable involved then you should use alarm
cable as it is stranded and intended for flexing. CAT5 is a solid core
cable
intended for installation where it will not be moved. A solid core cable
does not need to be flexed many times before it will break.

The method of termination is also important. Solid core cable is best
terminated by an IDC termination (punch down) or a Cage Clamp terminal
where
a metal leaf grips the cable rather than a a screw biting into it.

Stranded cable is more suited to wrapping round a screw or putting under a
screw terminal. you can terminate solid cable under a screw provided you do
it properly.

RIGHT WAY - cable goes round screw clockwise but does not overlap

----------
O
---

WRONG WAY - cable goes all the way round and overlaps.

----------
O
---
The pressure on the upper wire will cut through the lower wire and will
break at the slightest movement, usually as you push everything back into
place having made the terminations.

>About all I can think of for now and I am going to soak my muscles
after a
>marathon cable pulling session!

Good idea :-)

>Oh and so far 20 Cat 5 cables into the main living room with maybe
another
5
>to go excluding the windows. Is this enough?

If you can only think of a use for 3 of them then the answer is probably
yes.
If you are already planning to use 15 of them then use the time in the bath
to think of where you want to put the ones you havent yet pulled... and how
to add even more later when you find you need them!


Keith

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


> -----Original Message-----
> From: Mick Furlong [mailto:hiltoneltd@xxxxxxx]
> Sent: 23 May 2003 22:10
> To: ukha_d@xxxxxxx
> Subject: RE: [ukha_d] Sky Satellite cabling
>
>
> Thanks Keith I was just trying to save cable by not looping
> the feed through
> node Zero but of course it makes no difference to the overall
> length ...doh!
>
> Any chance you could help on the questions in my earlier post on cable
> marking and seperation please?
>
> cheers
>
> Mick