Re: Twin and Earth Cable Sizes

["David Buckley" <db@xxxxxxx>]

I'm assuming that the second dis board is some distance from the
incomming mains.

If you do what Paul suggests, you will need either ensure that the
cable to the second dis board is fed by cable of sufficient cross-
sectional area for the rated capacity of the incomming feed, which if
100A means more than 6mm cable, or more sensibly have a separate
isolator / single breaker breaker where the incommers are.


--- In ukha_d@xxxxxxx, "Paul Robinson" <ukcueman@y...>
wrote:
> I seem to have unwittingly hijacked this thread. Sorry about that!
>
> Anyway, I will consult my sparky on this. I would much prefer the 6A
> breakers to trip before the 32A.If this does turn out to be a
problem, I can
> always follow Neil's suggestion and not have the lighting circuit
go through
> a breaker in the main consumer unit, or else change the 32A breaker.
>
> Thanks,
> Paul
>
>
> ----- Original Message -----
> From: "David Buckley" <db@e...>
> To: <ukha_d@xxxxxxx>
> Sent: Thursday, July 03, 2003 1:45 PM
> Subject: [ukha_d] Re: Twin and Earth Cable Sizes
>
>
> >
> > 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