On Saturday, 30 June 2018 15:57:00 UTC+1, John Rumm wrote:
On 30/06/2018 11:42, tabbypurr wrote:
On Saturday, 30 June 2018 08:15:22 UTC+1, ARW wrote:
On 29/06/2018 21:51, John Rumm wrote:
On 29/06/2018 00:19, tabbypurr wrote:
On Monday, 25 June 2018 01:08:08 UTC+1, tabbyÂ* wrote:

Current fusebox has several fuseways each feeding a meter then a 2
way fusebox which powers each rented room. Plan is a new CU & new
secondary 2 way CUs, the meters will be retained. The question is how
may RCD protection be implemented. If done in the main CU with an
RCBO, a trip results in a room losing all power including lighting.
If done in the secondary small CU, the cable from main CU to meter to
secondary would not be RCD protected. This wiring is surface clipped
direct. Neither of those options strike me as fully satisfactory.
How's good to do this?


NT

OK, some questions.
Does there need to be separate rcd protection for lights & sockets so
lighting isn't lost when sockets trip?

Ideally, yes

Since SP RCBOs don't disconnect N-E faults, I presume the whole
install still requires 2x DP RCDs. Can these be 300mA time delayed or
must they be 30mA?

If there are additional downstream 30mA trip devices, then they can in
theory be 100mA type S devices. However you won't then be able to
achieve discrimination with the RCD protecting the submain feeds to the
meters. So you are no nearer a workable solution.

So that leaves you needing either 2 DP RCBOs per room, or two
conventional 30mA RCDs and two MCBs (likely 6 ways in total per room)..

The cheapest option may be a small CU for the head end - Type S RCD on
its incomer, then 4 x regular MCBs for your submain feeds.

It would probably be a a lot cheaper and easier to use a hi integrity
dual split load CU with a 100mA main switch, 4 MCBs for the rooms fed
from the mains switch and to use the 30mA RCD supplies for the communal
areas and just fit a 2 way garage CU in each room.

Unless I'm mistaken the surface wiring to & from the meters must be DP RCDed on this TT system, either at 30mA or 100mA time delayed.

Yup, if you look carefully at what Adam wrote "100mA" main switch rather
than the more common "100A" main switch, I think he was implying that
the main switch would be a 100mA trip type S device.

yes, I misread that

I think it would be ok to feed all 4 meters from the same RCD.

I would be happy with that since the chances of a fault on the submains
is likely to be rare enough for it to be an acceptable risk /
inconvenience.

I take it discrimination between lights & sockets in each room is not required, meaning both can run off the same RCD. That certainly simplifies things, as you say a garage CU would do the job. I was looking at a single larger secondary CU with SP RCBOs because that would be cheaper & neater, but if SP RCBOs are no good then so be it.

This is one of the cases where the designer will need to make a
judgement call based on the circumstances.

No discrimination between circuits in the room is less than the perfect
ideal, but may be acceptable since the risks are low - i.e. no stairs,
no rotating machinery etc, and its only one room etc.

yes, all power to a room being cut off in the event of credit running out is standard practice.

A similar situation will exist with a 17th edition style split load unit
- one RCD trip will affect several circuits (although you normally
arrange them such that the power circuit would not cause a trip on the
same lighting circuit that serves the power circuit)

You could also mitigate with a £15 non maintained emergency light in the
room if you wanted.

If discrimination against N-E faults is required, why are single pole RCBOs sold? There's something I'm not clear on yet here.

For TN-C-S installs there is unlikely to be any significant voltage
difference between N & E at the origin of the installation (since they
are joined there). So once the loads are disconnected there is unlikely
to be any significant current flow in the CPC. What there is, will be
conducted by the suppliers PEN conductor which is designed to be a
current carrying conductor in normal operation (i.e. it is a "live" wire)

With TT, the neutral at the point of supply could be at a different
potential to that of the local earth spike. So a persistent N E fault
could drive significant current through the local earth spike (which in
turn could cause heating, loss of moisture and rising external earth
impedance).

So on balance a SP RCBO will still result in a significant reduction in
serious injury risk for most installations - its just not as suitable
for TT installs

gotcha
Presumably for the same reason it wouldn't be well suited to TN-S either, only for PME supplies.


(although I would highlight that I have a 16th edition style TT system
here, with 100mA trip type S incomer, and then a DP 30mA normal RCD for
power circuits. I also have a SP RCBO on my kitchen circuit (since that
was nuisance tripping the 30mA RCD). I decided it was preferable to
accept that a N&E fault on that one circuit could result in tripping the
incomer RCD as well, and be rid of the nuisance trip issue that was
there before). (I do have several non maintained emergency lights as
well though)

I've also been reading about the 18th edition, such as it is so far. Fixing of cables in escape routes has come up. I presume the usual plastic cable clips will no longer be permissible, are we going to go back to metal buckle clips? Is their lack of insulation ok today?

Yup this is a significant (and long overdue) change especially for
commercial / office installs.

(The main issue being that in many office / commercial fires things like
suspended ceilings would be covered is a mass of wiring. The moment the
flimsy ali frames fail in the heat, this is dropped onto the people
below - typically fire fighters - where it will snag on their breathing
apparatus and risks trapping them).

For the commercial installs, better use of cable trays, metal trunking
etc will solve most of the problems.

For smaller installs and domestic situations, I would expect there will
emerge a new range of non combustible cable restraint systems.

In this case the submain wiring is unsupported & there's no possible way to clip the cables using any known cable clip product. Insulated copper cable & wafer head screws should meet the requirements.


NT

On 30/06/2018 23:44, wrote:
On Saturday, 30 June 2018 15:57:00 UTC+1, John Rumm wrote:

If discrimination against N-E faults is required, why are single pole RCBOs sold? There's something I'm not clear on yet here.

For TN-C-S installs there is unlikely to be any significant voltage
difference between N & E at the origin of the installation (since they
are joined there). So once the loads are disconnected there is unlikely
to be any significant current flow in the CPC. What there is, will be
conducted by the suppliers PEN conductor which is designed to be a
current carrying conductor in normal operation (i.e. it is a "live" wire)

With TT, the neutral at the point of supply could be at a different
potential to that of the local earth spike. So a persistent N E fault
could drive significant current through the local earth spike (which in
turn could cause heating, loss of moisture and rising external earth
impedance).

So on balance a SP RCBO will still result in a significant reduction in
serious injury risk for most installations - its just not as suitable
for TT installs

gotcha
Presumably for the same reason it wouldn't be well suited to TN-S either, only for PME supplies.

I don't recall DP being a requirement for TN-S. While you are likely to
see a bigger voltage between N & E at the premises, they are still tied
together typically within a few hundred yards. The supply cable earth is
also properly bonded to a substatial earth at the sub station, so there
are not the same risks as there might be with a puny local earth rod.





--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Sunday, 1 July 2018 00:36:23 UTC+1, John Rumm wrote:
On 30/06/2018 23:44, tabbypurr wrote:
On Saturday, 30 June 2018 15:57:00 UTC+1, John Rumm wrote:

If discrimination against N-E faults is required, why are single pole RCBOs sold? There's something I'm not clear on yet here.

For TN-C-S installs there is unlikely to be any significant voltage
difference between N & E at the origin of the installation (since they
are joined there). So once the loads are disconnected there is unlikely
to be any significant current flow in the CPC. What there is, will be
conducted by the suppliers PEN conductor which is designed to be a
current carrying conductor in normal operation (i.e. it is a "live" wire)

With TT, the neutral at the point of supply could be at a different
potential to that of the local earth spike. So a persistent N E fault
could drive significant current through the local earth spike (which in
turn could cause heating, loss of moisture and rising external earth
impedance).

So on balance a SP RCBO will still result in a significant reduction in
serious injury risk for most installations - its just not as suitable
for TT installs

gotcha
Presumably for the same reason it wouldn't be well suited to TN-S either, only for PME supplies.

I don't recall DP being a requirement for TN-S. While you are likely to
see a bigger voltage between N & E at the premises, they are still tied
together typically within a few hundred yards. The supply cable earth is
also properly bonded to a substatial earth at the sub station, so there
are not the same risks as there might be with a puny local earth rod.

ok cheers. So the TN-S place can use the SP RCBOs for the final circuits. Do they still need to be fed from 2x DP RCDs to provide N-E fault protection?


NT

On 30/06/2018 11:42, wrote:

If discrimination against N-E faults is required, why are single pole RCBOs sold? There's something I'm not clear on yet here.


Well it's only a problem as you have a TT supply with a RCD main switch.

I've also been reading about the 18th edition, such as it is so far. Fixing of cables in escape routes has come up. I presume the usual plastic cable clips will no longer be permissible, are we going to go back to metal buckle clips? Is their lack of insulation ok today?

There use is fine. If using trunking there are special clips that fit
inside the trunking.


--
Adam

On 30/06/2018 11:47, Fredxx wrote:
On 30/06/2018 08:15, ARW wrote:
On 29/06/2018 21:51, John Rumm wrote:
On 29/06/2018 00:19, wrote:
On Monday, 25 June 2018 01:08:08 UTC+1, tabbyÂ* wrote:
Current fusebox has several fuseways each feeding a meter then a 2
way fusebox which powers each rented room. Plan is a new CU & new
secondary 2 way CUs, the meters will be retained. The question is
how may RCD protection be implemented. If done in the main CU with
an RCBO, a trip results in a room losing all power including
lighting. If done in the secondary small CU, the cable from main CU
to meter to secondary would not be RCD protected. This wiring is
surface clipped direct. Neither of those options strike me as fully
satisfactory. How's good to do this?


NT

OK, some questions.
Does there need to be separate rcd protection for lights & sockets
so lighting isn't lost when sockets trip?

Ideally, yes

Since SP RCBOs don't disconnect N-E faults, I presume the whole
install still requires 2x DP RCDs. Can these be 300mA time delayed
or must they be 30mA?

If there are additional downstream 30mA trip devices, then they can
in theory be 100mA type S devices. However you won't then be able to
achieve discrimination with the RCD protecting the submain feeds to
the meters. So you are no nearer a workable solution.

So that leaves you needing either 2 DP RCBOs per room, or two
conventional 30mA RCDs and two MCBs (likely 6 ways in total per room).

The cheapest option may be a small CU for the head end - Type S RCD
on its incomer, then 4 x regular MCBs for your submain feeds.

It would probably be a a lot cheaper and easier to use a hi integrity
dual split load CU with a 100mA main switch, 4 MCBs for the rooms fed
from the mains switch and to use the 30mA RCD supplies for the
communal areas and just fit a 2 way garage CU in each room.

Won't that mean the feeds to each room will not be 30mA RCD protected
and will need to be surfaced wired, or in SWA.

Do you need the lighting in a HMO room to be on a separate RCD to mains
outlets, or is the light in the landing on a different RCD circuit
sufficient?

As it's a TT supply then a 100mA RCD and surface mounted cable is fine.

There is no requirement for the lights and sockets to be on seperate
RCDs apart from inconvenience in the case of a trip.

The communal lights should be on a separate RCD to the rooms.

--
Adam

On 30/06/2018 11:42, wrote:
On Saturday, 30 June 2018 08:15:22 UTC+1, ARW wrote:
On 29/06/2018 21:51, John Rumm wrote:
On 29/06/2018 00:19, tabbypurr wrote:
On Monday, 25 June 2018 01:08:08 UTC+1, tabbyÂ* wrote:

Current fusebox has several fuseways each feeding a meter then a 2
way fusebox which powers each rented room. Plan is a new CU & new
secondary 2 way CUs, the meters will be retained. The question is how
may RCD protection be implemented. If done in the main CU with an
RCBO, a trip results in a room losing all power including lighting.
If done in the secondary small CU, the cable from main CU to meter to
secondary would not be RCD protected. This wiring is surface clipped
direct. Neither of those options strike me as fully satisfactory.
How's good to do this?


NT

OK, some questions.
Does there need to be separate rcd protection for lights & sockets so
lighting isn't lost when sockets trip?

Ideally, yes

Since SP RCBOs don't disconnect N-E faults, I presume the whole
install still requires 2x DP RCDs. Can these be 300mA time delayed or
must they be 30mA?

If there are additional downstream 30mA trip devices, then they can in
theory be 100mA type S devices. However you won't then be able to
achieve discrimination with the RCD protecting the submain feeds to the
meters. So you are no nearer a workable solution.

So that leaves you needing either 2 DP RCBOs per room, or two
conventional 30mA RCDs and two MCBs (likely 6 ways in total per room).

The cheapest option may be a small CU for the head end - Type S RCD on
its incomer, then 4 x regular MCBs for your submain feeds.

It would probably be a a lot cheaper and easier to use a hi integrity
dual split load CU with a 100mA main switch, 4 MCBs for the rooms fed
from the mains switch and to use the 30mA RCD supplies for the communal
areas and just fit a 2 way garage CU in each room.

Unless I'm mistaken the surface wiring to & from the meters must be DP RCDed on this TT system, either at 30mA or 100mA time delayed. I think it would be ok to feed all 4 meters from the same RCD.

It would have to be 100mA S type for the meters

I take it discrimination between lights & sockets in each room is not required, meaning both can run off the same RCD. That certainly simplifies things, as you say a garage CU would do the job. I was looking at a single larger secondary CU with SP RCBOs because that would be cheaper & neater, but if SP RCBOs are no good then so be it.

I am trying to think of a way to simplify it.


--
Adam

On 01/07/2018 09:29, ARW wrote:

I am trying to think of a way to simplify it.



Ways to simplify and keep down costs bearing in mind that it's an HMO
and no one of any importance will live there.

Lets assume that we are now going to put the lights and sockets in each
room on a shared 30mA supply.

1.Use a 5A unswitched fused spur in the room to power the lights from
the sockets. This saves space in your CU and will not be a problem.

2.This now means you just need 1 DP switched RCD in the CU for each
room, these can be DP or SP width depending on what you want to pay (the
Wylex SP width DP switching ones I linked to were about £26)

3.Use a hi integrity split load CU with a 100mA main switch.

4.Put the RCBOs on the 100mA side of the board (this will take 4 to 8
ways up of the CU).

5.Feed the room meters from the RCBO and then from the meter to each room.

6.Use the 30mA RCD protected spaces to power the communal areas


So if using Wylex stuff about £250.


--
Adam

On Sunday, 1 July 2018 08:23:56 UTC+1, ARW wrote:
On 30/06/2018 11:42, tabbypurr wrote:

If discrimination against N-E faults is required, why are single pole RCBOs sold? There's something I'm not clear on yet here.


Well it's only a problem as you have a TT supply with a RCD main switch.

I've also been reading about the 18th edition, such as it is so far. Fixing of cables in escape routes has come up. I presume the usual plastic cable clips will no longer be permissible, are we going to go back to metal buckle clips? Is their lack of insulation ok today?

There use is fine. If using trunking there are special clips that fit
inside the trunking.

Yup. It turns out there's no space for trunking or clips, the bundle tied with electrical singles screwed to the wall looks the only viable fire resistant option. It will be out of view, but not to the extent that it becomes a drilling hazard.


NT

On 01/07/2018 11:06, wrote:


Yup. It turns out there's no space for trunking or clips, the bundle tied with electrical singles screwed to the wall looks the only viable fire resistant option. It will be out of view, but not to the extent that it becomes a drilling hazard.


electrical singles?

explain please.

--
Adam

On Sunday, 1 July 2018 11:52:56 UTC+1, ARW wrote:
On 01/07/2018 11:06, tabbypurr wrote:


Yup. It turns out there's no space for trunking or clips, the bundle tied with electrical singles screwed to the wall looks the only viable fire resistant option. It will be out of view, but not to the extent that it becomes a drilling hazard.


electrical singles?

explain please.

what I meant was an insulated neutral conductor from a bit of cable. There's no room for other fixings & plastic cable ties won't hold it up in a fire.


NT

On 01/07/2018 07:08, wrote:
On Sunday, 1 July 2018 00:36:23 UTC+1, John Rumm wrote:
On 30/06/2018 23:44, tabbypurr wrote:
On Saturday, 30 June 2018 15:57:00 UTC+1, John Rumm wrote:

If discrimination against N-E faults is required, why are single pole RCBOs sold? There's something I'm not clear on yet here.

For TN-C-S installs there is unlikely to be any significant voltage
difference between N & E at the origin of the installation (since they
are joined there). So once the loads are disconnected there is unlikely
to be any significant current flow in the CPC. What there is, will be
conducted by the suppliers PEN conductor which is designed to be a
current carrying conductor in normal operation (i.e. it is a "live" wire)

With TT, the neutral at the point of supply could be at a different
potential to that of the local earth spike. So a persistent N E fault
could drive significant current through the local earth spike (which in
turn could cause heating, loss of moisture and rising external earth
impedance).

So on balance a SP RCBO will still result in a significant reduction in
serious injury risk for most installations - its just not as suitable
for TT installs

gotcha
Presumably for the same reason it wouldn't be well suited to TN-S either, only for PME supplies.

I don't recall DP being a requirement for TN-S. While you are likely to
see a bigger voltage between N & E at the premises, they are still tied
together typically within a few hundred yards. The supply cable earth is
also properly bonded to a substatial earth at the sub station, so there
are not the same risks as there might be with a puny local earth rod.

ok cheers. So the TN-S place can use the SP RCBOs for the final circuits. Do they still need to be fed from 2x DP RCDs to provide N-E fault protection?

On TN-S NE fault currents are likely to be small in comparison to LE
(from an infrastructure point of view they are typically a RCD nuisance
trip hazard rather than a fire risk) so don't require explicit protection.

(obviously NE shorts can pose a shock risk to users and maintainers of
the system - and may lay undetected on non RCD systems).


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 01/07/2018 23:08, wrote:
On Sunday, 1 July 2018 11:52:56 UTC+1, ARW wrote:
On 01/07/2018 11:06, tabbypurr wrote:


Yup. It turns out there's no space for trunking or clips, the
bundle tied with electrical singles screwed to the wall looks the
only viable fire resistant option. It will be out of view, but
not to the extent that it becomes a drilling hazard.


electrical singles?

explain please.

what I meant was an insulated neutral conductor from a bit of cable.
There's no room for other fixings & plastic cable ties won't hold it
up in a fire.


NT


You can buy metal cable ties.

On Monday, 2 July 2018 09:26:16 UTC+1, dennis@home wrote:
On 01/07/2018 23:08, tabbypurr wrote:
On Sunday, 1 July 2018 11:52:56 UTC+1, ARW wrote:
On 01/07/2018 11:06, tabbypurr wrote:


Yup. It turns out there's no space for trunking or clips, the
bundle tied with electrical singles screwed to the wall looks the
only viable fire resistant option. It will be out of view, but
not to the extent that it becomes a drilling hazard.


electrical singles?

explain please.

what I meant was an insulated neutral conductor from a bit of cable.
There's no room for other fixings & plastic cable ties won't hold it
up in a fire.


NT


You can buy metal cable ties.

yes, though they're less useful rather than more.


NT

On Monday, 25 June 2018 01:08:08 UTC+1, tabby wrote:

Current fusebox has several fuseways each feeding a meter then a 2 way fusebox which powers each rented room. Plan is a new CU & new secondary 2 way CUs, the meters will be retained. The question is how may RCD protection be implemented. If done in the main CU with an RCBO, a trip results in a room losing all power including lighting. If done in the secondary small CU, the cable from main CU to meter to secondary would not be RCD protected. This wiring is surface clipped direct. Neither of those options strike me as fully satisfactory. How's good to do this?


NT

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it be external to protect against a tail to case short? If external can it be in plastic or must be metal? And if metal does it need another before it to...

Rented rooms can all go on one DP S RCD, with one SP RCBO then feeding each meter, which feeds each socket circuit which feeds each lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is to give discrimination against L-E leakage trips.

Communal areas I take it must be fed from 2 RCDs not 1 because losing lighting could be an issue due to cooking being potentially hazardous.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its own separate DP RCD?

thanks.


NT

On 03/07/2018 00:23, wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome, and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.


NT

On 04/07/2018 01:06, wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome,

You might find that 1 x RCD + 2 x MCB is cheaper than 2 x RCBO.

and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.

Nope... then again if paying for the labour, then that would probably
dwarf the material cost.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wednesday, 4 July 2018 01:41:31 UTC+1, John Rumm wrote:
On 04/07/2018 01:06, tabbypurr wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome,

You might find that 1 x RCD + 2 x MCB is cheaper than 2 x RCBO.

I found that reusing the SP RCBOs is far cheaper


and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.

Nope... then again if paying for the labour, then that would probably
dwarf the material cost.

When I've got a bit of time I'll have to look again at what's available. It's going to be a monster of a CU at this rate.


NT

On Wednesday, 4 July 2018 10:52:33 UTC+1, tabby wrote:
On Wednesday, 4 July 2018 01:41:31 UTC+1, John Rumm wrote:
On 04/07/2018 01:06, tabbypurr wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome,

You might find that 1 x RCD + 2 x MCB is cheaper than 2 x RCBO.

I found that reusing the SP RCBOs is far cheaper


and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.

Nope... then again if paying for the labour, then that would probably
dwarf the material cost.

When I've got a bit of time I'll have to look again at what's available. It's going to be a monster of a CU at this rate.


NT

was going to go for a Wylex NM CU, but with all the required RCDs there won't be enough ways left. If a different CU is used it will add hundreds to the cost due to need for new RCDs/RCBOs. So... could this lot be split into 2 CUs? How?


NT

On 04/07/2018 14:58, wrote:

was going to go for a Wylex NM CU, but with all the required RCDs
there won't be enough ways left. If a different CU is used it will
add hundreds to the cost due to need for new RCDs/RCBOs. So... could
this lot be split into 2 CUs? How?

Multiple CUs is probably the way I would go - the number does not really
change the principle of what you are trying to do (much - although note
that previous comment about having a terminal to use as a neutral).

You could probbaly do a large CU for the head end with sumbmain feeds,
and say a couple of rooms. Then a second smaller one for the next two
rooms.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/07/2018 01:06, wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome, and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.


I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.


--
Adam

On Wednesday, 4 July 2018 15:08:25 UTC+1, John Rumm wrote:
On 04/07/2018 14:58, tabbypurr wrote:

was going to go for a Wylex NM CU, but with all the required RCDs
there won't be enough ways left. If a different CU is used it will
add hundreds to the cost due to need for new RCDs/RCBOs. So... could
this lot be split into 2 CUs? How?

Multiple CUs is probably the way I would go - the number does not really
change the principle of what you are trying to do (much - although note
that previous comment about having a terminal to use as a neutral).

You could probbaly do a large CU for the head end with sumbmain feeds,
and say a couple of rooms. Then a second smaller one for the next two
rooms.

How would I feed the secondary(ies) from the first CU? Ie what electrical protection would the interconnecting cable need?

This 21 way might do the job, though it comes with the wrong RCDs:
https://www.screwfix.com/p/wylex-21-...mer-unit/2503j


NT

On Wednesday, 4 July 2018 18:42:18 UTC+1, ARW wrote:
On 04/07/2018 01:06, tabbypurr wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome, and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.


I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.

I await with interest. There's one way I can think of to do that, TN-C, but I don't think that's allowed now. Not on T&E anyway, which everything is wired with.


NT

On 04/07/2018 19:39, wrote:
On Wednesday, 4 July 2018 15:08:25 UTC+1, John Rumm wrote:
On 04/07/2018 14:58, tabbypurr wrote:

was going to go for a Wylex NM CU, but with all the required
RCDs there won't be enough ways left. If a different CU is used
it will add hundreds to the cost due to need for new RCDs/RCBOs.
So... could this lot be split into 2 CUs? How?

Multiple CUs is probably the way I would go - the number does not
really change the principle of what you are trying to do (much -
although note that previous comment about having a terminal to use
as a neutral).

You could probbaly do a large CU for the head end with sumbmain
feeds, and say a couple of rooms. Then a second smaller one for the
next two rooms.

How would I feed the secondary(ies) from the first CU? Ie what
electrical protection would the interconnecting cable need?

They would be fed from the return sub main from the meters. If they are
also surfaces wired then they don't require 30mA trip RCD protection. So
a type S 100mA trip device as main switch in primary CU. MCBs on feeds
to meters. Returns from meters feeding whatever you decide to go with
(RCBOs etc)

This 21 way might do the job, though it comes with the wrong RCDs:
https://www.screwfix.com/p/wylex-21-...mer-unit/2503j

Might be better buying an empty CU and reusing what you can and buying
what extra devices you need.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wednesday, 4 July 2018 23:06:38 UTC+1, John Rumm wrote:
On 04/07/2018 19:39, tabbypurr wrote:
On Wednesday, 4 July 2018 15:08:25 UTC+1, John Rumm wrote:
On 04/07/2018 14:58, tabbypurr wrote:

was going to go for a Wylex NM CU, but with all the required
RCDs there won't be enough ways left. If a different CU is used
it will add hundreds to the cost due to need for new RCDs/RCBOs.
So... could this lot be split into 2 CUs? How?

Multiple CUs is probably the way I would go - the number does not
really change the principle of what you are trying to do (much -
although note that previous comment about having a terminal to use
as a neutral).

You could probbaly do a large CU for the head end with sumbmain
feeds, and say a couple of rooms. Then a second smaller one for the
next two rooms.

How would I feed the secondary(ies) from the first CU? Ie what
electrical protection would the interconnecting cable need?

They would be fed from the return sub main from the meters. If they are
also surfaces wired then they don't require 30mA trip RCD protection. So
a type S 100mA trip device as main switch in primary CU. MCBs on feeds
to meters. Returns from meters feeding whatever you decide to go with
(RCBOs etc)

I'm not sure that would work. It needs 4x RCDs total, doing the above would not farm any of the RCDs out to the 2nd box, so wouldn't enable use of 2x split CUs. I'd still need a box with 4x RCDs, and haven't seen any.


This 21 way might do the job, though it comes with the wrong RCDs:
https://www.screwfix.com/p/wylex-21-...mer-unit/2503j

Might be better buying an empty CU and reusing what you can and buying
what extra devices you need.

On second look I realised I could work it with the RCDs supplied, and 21 ways is just enough. So maybe I've found the right CU at last.

Didn't like the prices of industrial units.


NT

On 05/07/2018 00:09, wrote:
On Wednesday, 4 July 2018 23:06:38 UTC+1, John Rumm wrote:
On 04/07/2018 19:39, tabbypurr wrote:
On Wednesday, 4 July 2018 15:08:25 UTC+1, John Rumm wrote:
On 04/07/2018 14:58, tabbypurr wrote:

was going to go for a Wylex NM CU, but with all the required
RCDs there won't be enough ways left. If a different CU is used
it will add hundreds to the cost due to need for new RCDs/RCBOs.
So... could this lot be split into 2 CUs? How?

Multiple CUs is probably the way I would go - the number does not
really change the principle of what you are trying to do (much -
although note that previous comment about having a terminal to use
as a neutral).

You could probbaly do a large CU for the head end with sumbmain
feeds, and say a couple of rooms. Then a second smaller one for the
next two rooms.

How would I feed the secondary(ies) from the first CU? Ie what
electrical protection would the interconnecting cable need?

They would be fed from the return sub main from the meters. If they are
also surfaces wired then they don't require 30mA trip RCD protection. So
a type S 100mA trip device as main switch in primary CU. MCBs on feeds
to meters. Returns from meters feeding whatever you decide to go with
(RCBOs etc)

I'm not sure that would work. It needs 4x RCDs total, doing the above would not farm any of the RCDs out to the 2nd box, so wouldn't enable use of 2x split CUs. I'd still need a box with 4x RCDs, and haven't seen any.

You can make your own sub divisions - you don't have to go with what is
provided. If you start with a "high integrity" CU - that will normally
have provision for at least three main switching elements (typically a
main switch, some space for MCBs/RCBOs, then a pair of RCDs with their
own bus bars in typical split load configuration).

I think you need to decide what topology of devices you are going to go
with, then it will be easier to work out how to "package" what you need.

This 21 way might do the job, though it comes with the wrong RCDs:
https://www.screwfix.com/p/wylex-21-...mer-unit/2503j

Might be better buying an empty CU and reusing what you can and buying
what extra devices you need.

On second look I realised I could work it with the RCDs supplied, and 21 ways is just enough. So maybe I've found the right CU at last.

Didn't like the prices of industrial units.

To an extent you get what you pay for. The industrial stuff tends to be
more configurable, and flexible, better made, and more wiring space (not
to mention capabilities for things like 3 phase, and high breaking
capacity control gear).


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/07/2018 19:45, wrote:
On Wednesday, 4 July 2018 18:42:18 UTC+1, ARW wrote:
On 04/07/2018 01:06, tabbypurr wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome, and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.


I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.

I await with interest. There's one way I can think of to do that, TN-C, but I don't think that's allowed now. Not on T&E anyway, which everything is wired with.

I do apologise for the delay. The World Cup and having to travel to
Durham everyday has left me little time. I also forgot that I had a
suggestion to make because of the number of World Cup matches I have to
watch in the pub.

Get rid of the 100mA main switch and just use a normal main switch with
SP switching RCBOs for all circuits.

Feed the rooms meters off say a 32A or 20A RCBO (depending on what the
socket circuit is powered at) you then either use the fused connection
unit in the room for the lights that I suggested or back feed from the
meter to a 6A MCB in the CU for the lights.

The rooms will share a RCD but who cares?


If you want DP isolation for the rooms then fit a cooker switch before
the meter.


--
Adam

On Friday, 6 July 2018 19:15:57 UTC+1, ARW wrote:
On 04/07/2018 19:45, tabbypurr wrote:
On Wednesday, 4 July 2018 18:42:18 UTC+1, ARW wrote:
On 04/07/2018 01:06, tabbypurr wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome, and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.


I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.

I await with interest. There's one way I can think of to do that, TN-C, but I don't think that's allowed now. Not on T&E anyway, which everything is wired with.

I do apologise for the delay. The World Cup and having to travel to
Durham everyday has left me little time. I also forgot that I had a
suggestion to make because of the number of World Cup matches I have to
watch in the pub.

we know how that works

Get rid of the 100mA main switch and just use a normal main switch with
SP switching RCBOs for all circuits.

I didn't realise one could omit RCD action for N-E faults. It would simplify things.

Feed the rooms meters off say a 32A or 20A RCBO (depending on what the
socket circuit is powered at) you then either use the fused connection
unit in the room for the lights that I suggested or back feed from the
meter to a 6A MCB in the CU for the lights.

I'll go with fuses otherwise the required CU becomes 25 ways.

The rooms will share a RCD but who cares?

hmm, I'd not thought of commoning the meter supplies.

If you want DP isolation for the rooms then fit a cooker switch before
the meter.

no need for that. N-E faults are almost always going to be in appliances.


If only SP RCD action is permitted this simplifies things. Cheers.


NT

On 07/07/2018 01:35, wrote:
On Friday, 6 July 2018 19:15:57 UTC+1, ARW wrote:
On 04/07/2018 19:45, tabbypurr wrote:
On Wednesday, 4 July 2018 18:42:18 UTC+1, ARW wrote:
On 04/07/2018 01:06, tabbypurr wrote:
On Tuesday, 3 July 2018 12:19:41 UTC+1, John Rumm wrote:
On 03/07/2018 00:23, tabbypurr wrote:

OK, here's where things are so far...

TT & metal CU means a 100mA S RCD - can that go in the CU or must it
be external to protect against a tail to case short? If external can
it be in plastic or must be metal? And if metal does it need another
before it to...

You may be able to get an extra insulation kit for TT installs to allow
them to be done in a metal enclosure.

Rented rooms can all go on one DP S RCD, with one SP RCBO then
feeding each meter, which feeds each socket circuit which feeds each
lighting circuit via a 5A fused FCU. The purpose of the SP RCBOs is
to give discrimination against L-E leakage trips.

A SP RCBO will discriminate on L E faults, but not N & E faults as
previously discussed. Since you are feeding both lights and sockets
from the same circuit, then a normal DP RCD and MCBs would be adequate
and also protect against tripping the head end RCD on a NE fault.

Yes, but that isn't wanted. The expense of multiple DP MCBs is unwelcome, and the lack of discrimination of a single DP RCD is also not wanted. Hence the plan to split the protection: L-E discriminating, N-E not.


Communal areas I take it must be fed from 2 RCDs not 1 because losing
lighting could be an issue due to cooking being potentially
hazardous.

They also want to be independent of the rooms, so that you can "escape"
to a light communal area, if a trip takes out all power to a room.

Fire alarm circuit requires its own MCB or SP RCBO: does it need its
own separate DP RCD?

You don't want any other fault being able to disable it.

That takes the count up to a minimum of 4 main RCDs, effectively a 4 way split CU. Not going to be cheap.


I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.

I await with interest. There's one way I can think of to do that, TN-C, but I don't think that's allowed now. Not on T&E anyway, which everything is wired with.

I do apologise for the delay. The World Cup and having to travel to
Durham everyday has left me little time. I also forgot that I had a
suggestion to make because of the number of World Cup matches I have to
watch in the pub.

we know how that works

Get rid of the 100mA main switch and just use a normal main switch with
SP switching RCBOs for all circuits.

I didn't realise one could omit RCD action for N-E faults. It would simplify things.

You still have NE protection


Feed the rooms meters off say a 32A or 20A RCBO (depending on what the
socket circuit is powered at) you then either use the fused connection
unit in the room for the lights that I suggested or back feed from the
meter to a 6A MCB in the CU for the lights.

I'll go with fuses otherwise the required CU becomes 25 ways.

The rooms will share a RCD but who cares?

hmm, I'd not thought of commoning the meter supplies.

I was still thinking of one RCD for each meter and each room, I meant
that the lights and sockets in that room would share a RCD


If you want DP isolation for the rooms then fit a cooker switch before
the meter.

no need for that. N-E faults are almost always going to be in appliances.


If only SP RCD action is permitted this simplifies things. Cheers.

It is allowed as long as every circuit is RCD protected and there is no
100mA mainswitch.


--
Adam

On Saturday, 7 July 2018 06:11:39 UTC+1, ARW wrote:
On 07/07/2018 01:35, tabbypurr wrote:
On Friday, 6 July 2018 19:15:57 UTC+1, ARW wrote:
On 04/07/2018 19:45, tabbypurr wrote:
On Wednesday, 4 July 2018 18:42:18 UTC+1, ARW wrote:

I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.

I await with interest. There's one way I can think of to do that, TN-C, but I don't think that's allowed now. Not on T&E anyway, which everything is wired with.

I do apologise for the delay. The World Cup and having to travel to
Durham everyday has left me little time. I also forgot that I had a
suggestion to make because of the number of World Cup matches I have to
watch in the pub.

we know how that works

Get rid of the 100mA main switch and just use a normal main switch with
SP switching RCBOs for all circuits.

I didn't realise one could omit RCD action for N-E faults. It would simplify things.

You still have NE protection

yes, the penny has dropped. The relevant SP RCBO would disconnect the load, thought not disconnect the N-E fault.


Feed the rooms meters off say a 32A or 20A RCBO (depending on what the
socket circuit is powered at) you then either use the fused connection
unit in the room for the lights that I suggested or back feed from the
meter to a 6A MCB in the CU for the lights.

I'll go with fuses otherwise the required CU becomes 25 ways.

The rooms will share a RCD but who cares?

hmm, I'd not thought of commoning the meter supplies.

I was still thinking of one RCD for each meter and each room, I meant
that the lights and sockets in that room would share a RCD

yes will do that, using your FCU strategy


If you want DP isolation for the rooms then fit a cooker switch before
the meter.

no need for that. N-E faults are almost always going to be in appliances.


If only SP RCD action is permitted this simplifies things. Cheers.

It is allowed as long as every circuit is RCD protected and there is no
100mA mainswitch.

That would make life a lot easier. John reckoned DP RCD cover was required for TT - I may have to go reading.

Cheers


NT

On 07/07/2018 11:32, wrote:
On Saturday, 7 July 2018 06:11:39 UTC+1, ARW wrote:
On 07/07/2018 01:35, tabbypurr wrote:
On Friday, 6 July 2018 19:15:57 UTC+1, ARW wrote:
On 04/07/2018 19:45, tabbypurr wrote:
On Wednesday, 4 July 2018 18:42:18 UTC+1, ARW wrote:

I think I have a solution that would please you. Give a bit of time I
have just got in from work. It does away with the 100mA RCD main switch
and only used SP RCDs.

I await with interest. There's one way I can think of to do that, TN-C, but I don't think that's allowed now. Not on T&E anyway, which everything is wired with.

I do apologise for the delay. The World Cup and having to travel to
Durham everyday has left me little time. I also forgot that I had a
suggestion to make because of the number of World Cup matches I have to
watch in the pub.

we know how that works

Get rid of the 100mA main switch and just use a normal main switch with
SP switching RCBOs for all circuits.

I didn't realise one could omit RCD action for N-E faults. It would simplify things.

You still have NE protection

yes, the penny has dropped. The relevant SP RCBO would disconnect the load, thought not disconnect the N-E fault.


Feed the rooms meters off say a 32A or 20A RCBO (depending on what the
socket circuit is powered at) you then either use the fused connection
unit in the room for the lights that I suggested or back feed from the
meter to a 6A MCB in the CU for the lights.

I'll go with fuses otherwise the required CU becomes 25 ways.

The rooms will share a RCD but who cares?

hmm, I'd not thought of commoning the meter supplies.

I was still thinking of one RCD for each meter and each room, I meant
that the lights and sockets in that room would share a RCD

yes will do that, using your FCU strategy


If you want DP isolation for the rooms then fit a cooker switch before
the meter.

no need for that. N-E faults are almost always going to be in appliances.


If only SP RCD action is permitted this simplifies things. Cheers.

It is allowed as long as every circuit is RCD protected and there is no
100mA mainswitch.

That would make life a lot easier. John reckoned DP RCD cover was required for TT - I may have to go reading.

The main switch is your DP cover. It need not be RCD DP protection.




--
Adam