RE: Lights, cabling, CBus, etc.

["Kevin Hawkins" <lists@xxxxxxx>]

Just a quick comment before anyone gets the wrong end of the story here -
1.5mm is used for lighting circuits based on 240V distribution voltage -
the
mm diameter relates to the current that the conductors can carry safely -
too large a current / too small a conductor causes heating and possible
failure / fire risk.
When running low voltage lighting currents are MUCH higher - a 50W mains
lamp consumes 200ma - while a 50W 12V halogen consumes 4.2A - over twenty
times as much current. If you are running each lamp back to the transformer
then you have 4.2 A in each wire - if however you ran 5 lamps off one cable
in a daisychain fashion then the cable leaving the transformer would have
over 20A flowing in it - which is a lot and well above 1.5mm cabling
recommendations. That's why low voltage cables are 'beefy' and usually
quite
short. It also retains brightness at the extremes of the cable runs as the
voltage drops over distance.
David - your approach of running each one separately will be fine as you
suggested but don't daisychain low voltage without using adequately rated
cable.

kevin

> -----Original Message-----
> From: Paul Gordon [mailto:paul_gordon@xxxxxxx]
> Sent: 07 April 2003 11:50
> To: ukha_d@xxxxxxx
> Subject: Re: [ukha_d] Lights, cabling, CBus, etc.
>
> First off, - I am not in any way qualified in electrical installation
> or
> standards, so anything I say here may well be incorrect, which I'm
sure
> someone else will point out if so...
>
>
> >
> >And leading on from that, what cabling should I use for the
lights.
> >Is 2.5mm T&E suitable?
>
> I'd be surprised if you *need* to use 2.5mm for lighting circuits. I
> believe
> it is more normal to use 1.5mm for lighting, and 2.5mm for sockets...
> In a
> similar installation I recently did, I ran 1.5mm T&E to the joist
> immediately above each fitting, then fitted a 20A junction box, and
ran
> a
> short length of 13A flex to each light fitting, - mainly because the
> terminals on the light fittings seem to work better with stranded
> cable, and
> its quite a bit easier to work with the fittings during installation.
>
>
> >Also, for the cat5, I know Clipsal recommend
> >their own, but are there other sources of lsoh/coloured cable to
the
> >same spec?
> >
>
> I speak only as a cynical observer, but I'd bet money that their
> flavour of
> CAT5 costs double what you'd pay at any of the usual electrical
> wholesalers/IT suppliers.... ;-)
>
> AFAIK, CAT5 defines a standard, so if the CBUS states CAT5 cable as a
> requirement, then I would be inclined to believe that any cable that
> meets
> the CAT5 specs would be OK, and any suggestion by Clipsal to the
> contrary is
> merely an attempt to screw more money out of you...
>
>
> >For the halogens, I wanted to use mains powered, to avoid the buzz
> >that LV ones generate when dimmed. I presume there's no problem
> >about dimmming the mains ones? I'm thinking of something like the
> >standard halogens, such as those on p70 of the Screwfix catalog
> >(vol70), although I'd gladly accept advice on better ones.
> >
>
> If these the ones I am thinking of, I'd avoid them for no other reason
> than
> the construction of them is pretty cheap. - The body is made of such
> thin &
> soft metal that when holding the retaining spring clips back as one is
> required to do when inserting them into the cut-out, the lugs to which
> the
> springs are attached actually bent backwards, meaning that when
> released,
> the springs no longer worked properly, and the fittings were often
> loose in
> the hole... Also, the circle-clip that retains the bulb in the fitting
> was
> also not a very good fit, and constantly kept popping out, allowing
the
> bulb
> to fall out! I used these ones in my kitchen ceiling, but I would not
> use
> them again... - you gets what you pays for I suppose, and these are
> pretty
> cheap (about 3-4 per fitting IIRC?)
>
>
> HTH
>
> Paul G.
>
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