On 07/02/2019 23:27, Roger Hayter wrote:
ARW wrote:
On 07/02/2019 13:30, Roger Hayter wrote:
Roger Hayter wrote:
ARW wrote:
On 06/02/2019 12:58, Roger Hayter wrote:
I have an economy seven supply. Two 25mm wires go from the main fuse
block to the meter (presumably live and neutral) and then to a switch
and then to two Henley blocks. From one of these a 25mm wire goes to a
radio controlled switch, and out of this time switch another 25mm wire
goes to a third Henley block. The house supply runs from the first two
blocks, and a separate wire from the third block presumably supplies
live to the night time only supply.
However, there are two 10mm wires from the main fuse block to the radio
switch, and one 6mm wire joins the radio switch to the meter.
Can I assume that none of the Henley blocks is live when the main fuse
is open? In theory any one of the last three wires by-passes the main
switch and could internally connect the night time supply to the live
via the radio switch box. And theoretically could back feed the main
house CUs via the live in connection to the radio switch. Is it safe
to assume with a high degree of reliablity that the internal
construction of the radio switch is such as to make this impossible?
(Obviously I wouldn't work on anything without checking it is not live,
but the radio switch is, after all, a switch and if it could connect
live to the wrong wiring could presumably do it suddenly and
unexpectedly.)
With the main fuse out everything should be dead.
True, but I only want to change an MCB for an RCBO in the economy 7 CU
and would prefer to rely on the main switch if it isafe to do so.
Removing the main fuse is potentially hazardous, isn't it?
In response to a very sensible email suggestion, here are some photos.
As an added bonus, does anyone think a Wylex RCBO will fit in the one
unit CU photoed?
Thanks all for advice.
http://www.photobox.co.uk/album/5568689698
You cannot fit a RCBO into that CU. That looks like an old plug in fuse
that has been swapped for a MCB.
Thanks for the pictures.
OK so its a new CU or delete the economy 7 cirtuit. Thanks, that's
useful to know. It is mainly borderline OCD that makes me want to
change it just because it is the only circuit in the house not protected
by an RCD.
PS I suppose I can't use an RCBO on its own without a mains switch a) to
make servicing the RCBO safer and b) because I won't find an RCBO with
16mm terminals. Is there a more fundamental reason?
(I realise me doing it is all theoretical because of part P, of course,
but I can influence the specs! Another practical electrician question
is whether someone who replaced this CU would have to test the whole
house installation?)
I've carefully avoided checking that the economy 7 circuit is wired as a
ring so far, but I suppose I could always use a smaller MCB.
A couple of options.
First of all find out if is a ring or not. Now is the time to find out!
If not a ring then swap the Wylex box for a new CU with 2 x 20A radial
circuits with RCBOs or a RCD main switch. Don't consider a 2 way garage
CU as you have 25mmm tails. You might just squeeze a 4way with main
switch CU in there.
If it is a ring then
a) swap the sockets for sockets with RCD built into them. Job done in
minutes.
b) swap the Wylex unit for a 32A double width RCBO in a suitable
enclosure (going to be tricky with 25mm tails)
or
c) follow the advice for the radial circuit and have 3 spare ways and
one 32A RCBO.
--
Adam