I apologise if this has been discussed before but there is a reference
in the discussion on moving a 13A socket by 6 inches to adding an RCD
in accordance with Edition 17, which I am taking as an 'all-house'
RCD.

What options exist for doing this in a current design split supply CU
with MCB's and an RCD for the sockets, cooker,etc? Can the main
isolator switch be replaced, an external RCD fitted, or is it a new
CU?

Rob

robgraham coughed up some electrons that declared:

I apologise if this has been discussed before but there is a reference
in the discussion on moving a 13A socket by 6 inches to adding an RCD
in accordance with Edition 17, which I am taking as an 'all-house'
RCD.

What options exist for doing this in a current design split supply CU
with MCB's and an RCD for the sockets, cooker,etc? Can the main
isolator switch be replaced, an external RCD fitted, or is it a new
CU?

Rob

IANAQE (not qualified sparky)

Whole house RCD are deemed undesireable as a nusiance trip talks out the
house, or your angle grinder trips the RCD plunging you into darkness while
your up a ladder in the stairway, for an extreme example.

Seems 17th boards are tending towards 3 split ways (mixture of
lighting/power across two splits and the third split for fire alarms or
other special cases. You might get away with adding a 2nd RCB to a 2-split
way board, but you should still have a single isolator that kill the entire
board, so it's not as simple as chucking that out and replacing with an
RCD. There might be too many mechanical problems (busbar arrangement, lack
of space) to make converting it viable.

RCBOs are an option (the one I prefer).

Just stepping back - do you need to have your whole existing installation
conform to the 17th suddenly?

If so, would your CU allow 1-module RCBOs to be fitted in place of the MCBs
(need more vertical space).

Please wait for some more comments from better informed people than me
before you do anything... I'm not the authority here and my writing skills
sometimes don't come across clearly, I'm aware of that.

Cheers

Tim

robgraham wrote:
I apologise if this has been discussed before but there is a reference
in the discussion on moving a 13A socket by 6 inches to adding an RCD
in accordance with Edition 17, which I am taking as an 'all-house'
RCD.

A conventionally wired house - T&E cable under plaster - now needs 30 mA
RCD protection for all circuits, but certainly not a single whole-house
RCD. Viable options are to use two or more RCDs each feeding a group
of circuits, to use RCBOs exclusively, or some combination of the two.
Circuit grouping should be arranged so that any RCD trip will minimise
inconvenience and will not cause complete loss of lighting.

What options exist for doing this in a current design split supply CU
with MCB's and an RCD for the sockets, cooker,etc? Can the main
isolator switch be replaced, an external RCD fitted, or is it a new
CU?

If RCBOs are available to fit your existing CU then fitting one to each
non-RCD protected circuit in the split-load board is probably the
simplest option. Changing the main switch to an RCD won't work because
you need independent parallel-fed RCDs.

You might find this useful:
http://mk.learninglounge.com/resources/sott17esv.html
and this:
http://www.esc.org.uk/forum/

NB, assuming that the present earthing arrangements are OK, there is
absolutely no need to add RCD protection to existing lighting circuits
etc. just for the sake of it. The new requirements only come into play
if you are altering or extending an existing circuit, or providing a new
circuit.

--
Andy

On 24 Jul, 12:10, Andy Wade wrote:
robgraham wrote:
I apologise if this has been discussed before but there is a reference
in the discussion on moving a 13A socket by 6 inches to adding an RCD
in accordance with Edition 17, which I am taking as an 'all-house'
RCD.

A conventionally wired house - T&E cable under plaster - now needs 30 mA
RCD protection for all circuits, but certainly not a single whole-house
RCD. * Viable options are to use two or more RCDs each feeding a group
of circuits, to use RCBOs exclusively, or some combination of the two.
Circuit grouping should be arranged so that any RCD trip will minimise
inconvenience and will not cause complete loss of lighting.

What options exist for doing this in a current design split supply CU
with MCB's and an RCD for the sockets, cooker,etc? *Can the main
isolator switch be replaced, an external RCD fitted, or is it a new
CU?

If RCBOs are available to fit your existing CU then fitting one to each
non-RCD protected circuit in the split-load board is probably the
simplest option. *Changing the main switch to an RCD won't work because
you need independent parallel-fed RCDs.

You might find this useful:http://mk.learninglounge.com/resources/sott17esv.html
and this:http://www.esc.org.uk/forum/

NB, assuming that the present earthing arrangements are OK, there is
absolutely no need to add RCD protection to existing lighting circuits
etc. just for the sake of it. *The new requirements only come into play
if you are altering or extending an existing circuit, or providing a new
circuit.

--
Andy

Thanks for the replies, guys - I now have to admit to being a bit
unthinking it mentioning a 'whole house' RCD as I remember full well
enough having to all to regularly go round to the old man's house next
door to reset his RCD which did just kill everything..

The reason for asking is that I'm not too sure about the equipotential
bonding in this property and I'm wondering if fitting RCD's to the
lighting circuits would let me out of the chore of setting the bonding
to rights.

Rob