Re: Lights, cabling, CBus, etc.

["David Buckley" <db@xxxxxxx>]

--- In ukha_d@xxxxxxx, "Paul Gordon" <paul_gordon@h...>
wrote:
> 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...
>
> >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...
>

Err - no.

It is true that any Cat5 type of cable (or probably lesser cable such
as Cat3, a/k/a BT CW1308) will be entirely adequate to meet the
technical requirements for CBUS to work over, but that is not the
whole story.

As the Clipsal kit is intended for permanent installation as part of
an electrical distribution system, the kit and its installation must
be in accordance with the Wiring Regs, BS 7671:2001.

Clipsal's training bumf states (quite reasonably) that "The Clipsal C-
Bus Control System is very safe, as the control cable for all devices
is a Category 5 cable,which operates at a SELV (SafetyExtra Low
Voltage) level of 36VDC".  Wiring reg 411-02-06-a states "SELV
circuit conductors shall be insulated in accordance with the
requirements with the requirements of the Regulations for the highest
voltage present".

Much of the C-bus controlled kit is DIN rail mounted, and designed to
be incorporated into consumer unit type boxes, which are certainly
part of an electrical installation, and the highest voltage present
in such an enclosure would be 230VAC, and thus the Cat5 cable must be
rated for at least that voltage.  A quick google search failed to
find a standard voltage rating for "ordinary" cat5.

This behaviour is not unique to Clipsal; EIB is virtually identical
in terms of what it does and how it achieves it.  It too has its own
specialist cable, with a 4KV wet rating.