RE: Cabling Question

["Keith Doxey" <lists.diyha@xxxxxxx>]

Hi Steve,

As I said.... you SHOULD keep separation. I also said that any mains
cable
is effectively balanced and should radiate little or no interference.

I cannot condone breaking any IEE regs as peoples safety is at risk,
however
I would certainly not get paranoid like some of the people on
comp.home.automation who shudder at the thought that cables may only be
11
3/4 inches apart instead of 12 inches.

Having maintained the sound and lighting installations in several local
nightclubs and pubs after all sorts of cowboys have been let loose in
the
past, I have seen 50x50 trunking packed to capacity with Audio,
Lighting,
Mains and Telephone cables with less than a fag papers separation let
alone
12  inches. Whenever I have redone any of these installations the
cables
have been segregated into different trunkings to give the required
physical
barrier but from an electromagnetic perspective they have still been in
close proximity. Even prior to segragation there were no problems from
interference.

What you describe, using separate holes is giving segragation.
Commercial
office trunking is about 8" wide and has a lower channel for LV, an
upper
channel for HV and a centre section where the electrical accessories
are
fitted. The floorboxes fitted in offices have several physically
separate
but adjacent compartments. Neither of these suffer problems yet the folks
on
c.h.a often advocate leaving a full stud width (16") between Low and
High
voltage outlets !

Susceptibility to interference is more down to the type of cable used
and
the type of signal than the physical installation. A poorly screened
cable
trying to carry low level audio over long distances will pick up all
sorts
of interference. The air is full of radio waves and other EMI. By
comparison
a properly balances audio signal sent at 0dB can travel for miles over
unscreened twisted pair.

Wherever possible you should attempt to maximise the distance to minimse
the
risk because if you are unlucky enough to suffer interference then the
time
and effort required to rectify the problem will be more than doing it
right
in the first place, but in the real world that isnt always possible.

REMEMBER : THERE MUST BE PHYSICAL SEPARATION BETWEEN MAINS AND LV.
An insulating barrier that does not form part of the cable itself
constites
a physical separation.



Keith

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


-----Original Message-----
From: Steve B [mailto:steve@xxxxxxx]
Sent: 04 May 2002 13:57
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] Cabling Question


Keith,

How likely are problems in a domestic situation ?

In a retro fit to an old house you often want to keep disturbance to a
minimum and often there is only one route to go. One hole or holes side
by
side etc. I have many cables parallel for say 20m and have found no
problems YET :-)

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