Re: Twin and Earth Cable Sizes

["David Buckley" <db@xxxxxxx>]

The problem with secondary distribution boards is that of
discrimination, or, how to make sure the 6A mcb in the slave unit
goes before the mcb in the master unit.  To ensure this happens as
planned you must either (a) have a massive differential on trip load
(and 6 vs 32 is not massive), or (b) use a "slower" MCB in the
master, so if the slave is all type one, use a type two in the master.

Secondly, earthing - standard T&E has an earth conductor of less
cross sectional area than the live, and thus you may hav to run an
earth as well.  I lost track of this bit of the regs.

Thirdly - your real enemies are voltage drop on the link cable, and
overheating.   Calculate carefully.  Be generous; voltage drop can
make your lights change intensity as other loads change.




--- In ukha_d@xxxxxxx, "Paul Robinson" <ukcueman@y...>
wrote:
> First the disclaimer: I am not an electrician.
>
> The size of the cable to feed your secondary board would depend on
the load
> the cable would take. My lighting will be fed from a single circuit
on the
> consumer unit via a 6mm cable and protected by a 32A MCB. That goes
to a
> secondary board which will have 6 10A MCBs, one per 4/8-channel
dimmer.
>
> The 32A figure is because every light turned on at 100% (which
won't happen
> in practice) will use a little below 32A.
>
> If your secondary board was going to use much less power, then you
could use
> a smaller cable. And vice-versa.
>
> HTH
> Paul
>
> ----- Original Message -----
> From: "wayne" <wayne@p...>
> To: <ukha_d@xxxxxxx>
> Sent: Wednesday, July 02, 2003 6:06 PM
> Subject: Re: [ukha_d] Twin and Earth Cable Sizes
>
>
> > Ok, just jumping on this thread, If I wanted to add a 2nd
distribution
> board
> > to an existing - what size do you use there?
> >
> > Thanks
> >
> > Wayne.
> >
> >
> > ----- Original Message -----
> > From: "Jon Payne" <jgpayne@b...>
> > To: <ukha_d@xxxxxxx>
> > Sent: Wednesday, July 02, 2003 4:06 PM
> > Subject: Re: [ukha_d] Twin and Earth Cable Sizes
> >
> >
> > > I'd agreed with James. I did this initially and it can get a
real pain
> in
> > > the a*** working this 2.5mm cable everywhere. 1.5mm is so
much
easier to
> > > work with - get some :)
> > >
> > > Jon
> > > ----- Original Message -----
> > > From: "James Hoye" <james.hoye@s...>
> > > To: <ukha_d@xxxxxxx>
> > > Sent: Wednesday, July 02, 2003 3:04 PM
> > > Subject: RE: [ukha_d] Twin and Earth Cable Sizes
> > >
> > >
> > > > > I have a simple question, If i am doing some
wiring in
lighting
> > > > > circuits is it OK to use 2.5 mm Twin and Earth? It
would
save me
> > having
> > > > > to buy 2 different types of cable, as I know 2.5mm
can be
used for
> > > > > power circuits (sockets) etc.
> > > >
> > > > >From an electrical safety point of view I can't see
any
issues -
> 2.5mm
> > is
> > > > certainly capable of carrying a 5 or 6A load!!!
> > > >
> > > > What may be a problem is coaxing the larger size cable
into
terminals
> > > meant
> > > > for 1.0/1.5mm cables - oh, and it might well confuse
any
person doing
> > any
> > > > electrical work in the future.
> > > >
> > > > A 100m roll of 1.5mm T&E is only ?11.99 from
Screwfix [other
suppliers
> > are
> > > > available etc]
> > > >
> > > > James H