In preparation for an extension to my house, I wish to replace my
consumer unit (wired fuse type) with a larger one with spare ways for
the circuits in the extension. The CU replacement will be fairly
straightforward but I have a couple of items I wish to check first.


The power reaches the house by way of a long overhead cable, running
underground from the very last post to our house. Incoming is a fat
black cable which splits to two smaller but still fat cables running
into the company fuse and a henley(?) block.

From these two blocks I have fat red and black cables to the meter,
then same large red & black to a Chilton Current Operated Earth
Leakage Current Detector. Finally cables run from the ELCD to the
Consumer unit. A separate earth cable runs from the CU to an earth
spike. (I will replace this with a much fatter earth cable at the
same time as it looks a little thin to me)

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

LHW

In article .com,
writes:

In preparation for an extension to my house, I wish to replace my
consumer unit (wired fuse type) with a larger one with spare ways for
the circuits in the extension. The CU replacement will be fairly
straightforward but I have a couple of items I wish to check first.


The power reaches the house by way of a long overhead cable, running
underground from the very last post to our house. Incoming is a fat
black cable which splits to two smaller but still fat cables running
into the company fuse and a henley(?) block.

From these two blocks I have fat red and black cables to the meter,
then same large red & black to a Chilton Current Operated Earth
Leakage Current Detector. Finally cables run from the ELCD to the
Consumer unit. A separate earth cable runs from the CU to an earth
spike. (I will replace this with a much fatter earth cable at the
same time as it looks a little thin to me)

This is a TT installation. Current Operated Earth Leakage Detector
is the original name for an RCD -- does it actually say that on it,
as Chilton are better known (to me at least) as a manufacturer of
Voltage Operated Earth Leakage Detectors, which is a previous
generation device. What rating is written on it?
The earth wiring you describe is however consistent with an RCD.

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

As you have a TT installation, all your circuits will need to be
RCD protected. It would be worth asking your supplier if you can
be easily converted to TN-C-S in where this would not be the case,
but that depends if the local supply network has been converted to
to Protective Multiple Earthing.

If you remain TT (own earth rod), you can still use a split CU,
but both sides will need RCD protection. One is protected at 30mA
for the circuits where protection against electrocution is required
or desirable, and the other is protected at 100mA (and can be time-
delayed) where protection against electrocution is not required (it
has to be time-delayed if the 30mA side is daisy-chained off it).
If you have the space available, I would consider doing these as 2
separate CU's, which gives you slightly more flexibility.

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

You generally don't want circuits running outdoors sharing an RCD
with indoor circuits, as outdoor faults are more common (moisture
ingress), and could leave indoor circuits unusable. Socket outlets
in your shed and garage should be RCD protected as they're likely
to be used to power outdoor appliances. This really implies they
should be on the 100mA RCD side and protected by an additional 30mA
RCD. If you were going the separate CU route, then add a third
dedicated 30mA RCD protected CU for them. There are lots of options
here, depending what you will be running in there (a freezer, for
example?) and how dry they are. If you do end up sharing an RCD
between indoor and outdoor circuits, do at least include a 2-pole
isolating switch in the outdoor feeds so you can isolate a faulty
circuit.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 4 Mar, 11:27, andrew@a17 (Andrew Gabriel) wrote:
In article .com,
writes:





In preparation for an extension to my house, I wish to replace my
consumer unit (wired fuse type) with a larger one with spare ways for
the circuits in the extension. The CU replacement will be fairly
straightforward but I have a couple of items I wish to check first.

The power reaches the house by way of a long overhead cable, running
underground from the very last post to our house. Incoming is a fat
black cable which splits to two smaller but still fat cables running
into the company fuse and a henley(?) block.

From these two blocks I have fat red and black cables to the meter,
then same large red & black to a Chilton Current Operated Earth
Leakage Current Detector. Finally cables run from the ELCD to the
Consumer unit. A separate earth cable runs from the CU to an earth
spike. (I will replace this with a much fatter earth cable at the
same time as it looks a little thin to me)

This is a TT installation. Current Operated Earth Leakage Detector
is the original name for an RCD -- does it actually say that on it,
as Chilton are better known (to me at least) as a manufacturer of
Voltage Operated Earth Leakage Detectors, which is a previous
generation device. What rating is written on it?
The earth wiring you describe is however consistent with an RCD.

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

As you have a TT installation, all your circuits will need to be
RCD protected. It would be worth asking your supplier if you can
be easily converted to TN-C-S in where this would not be the case,
but that depends if the local supply network has been converted to
to Protective Multiple Earthing.

If you remain TT (own earth rod), you can still use a split CU,
but both sides will need RCD protection. One is protected at 30mA
for the circuits where protection against electrocution is required
or desirable, and the other is protected at 100mA (and can be time-
delayed) where protection against electrocution is not required (it
has to be time-delayed if the 30mA side is daisy-chained off it).
If you have the space available, I would consider doing these as 2
separate CU's, which gives you slightly more flexibility.

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

You generally don't want circuits running outdoors sharing an RCD
with indoor circuits, as outdoor faults are more common (moisture
ingress), and could leave indoor circuits unusable. Socket outlets
in your shed and garage should be RCD protected as they're likely
to be used to power outdoor appliances. This really implies they
should be on the 100mA RCD side and protected by an additional 30mA
RCD. If you were going the separate CU route, then add a third
dedicated 30mA RCD protected CU for them. There are lots of options
here, depending what you will be running in there (a freezer, for
example?) and how dry they are. If you do end up sharing an RCD
between indoor and outdoor circuits, do at least include a 2-pole
isolating switch in the outdoor feeds so you can isolate a faulty
circuit.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Thanks Andrew, just the type of clear advice I was hoping for.

Having read all the other threads about ELCD I was very careful in
reading the data plate on it. It clearly reads Current Operated and
is a Type E (could be Type L as the typeface is not the greatest). It
is rated at 500mA if that means anything.

I will ask the supplier about the incoming supply and see how easy
(costly) the conversion would be. I quite like the 2 x consumer unit
options, I have the space do I just run two pairs of cables from the
meter, or do I daisy chain it someway ?

For the 'outside' circuits, assuming I go the separate 100mA CU route,
can I dedicate a way(or 2)in the CU for each outside circuit and put
30mA RCDs directly in the CU (or perhaps RCBOs) and run a ring from
that or do I have to run from a MCB to a 'garage' CU with its own
RCD ?

Lloyd

In article .com,
writes:
Thanks Andrew, just the type of clear advice I was hoping for.

Having read all the other threads about ELCD I was very careful in
reading the data plate on it. It clearly reads Current Operated and
is a Type E (could be Type L as the typeface is not the greatest). It
is rated at 500mA if that means anything.

OK, so it's a 500mA RCD. Presumably, it has zero or just one
earth connection point. A Voltage Operated ELCB has two separate
earth connections, one to the earth rod, and the other to the CU
or earth terminal.

I will ask the supplier about the incoming supply and see how easy
(costly) the conversion would be. I quite like the 2 x consumer unit
options, I have the space do I just run two pairs of cables from the
meter, or do I daisy chain it someway ?

You use a service connection block (Henley Block) to make the
connections of the tails. You would probably not get multiple
tails into the meter connections. Also, you probably won't be
able to access those connections without breaking the meter
seal, which is a big no.

For the 'outside' circuits, assuming I go the separate 100mA CU route,
can I dedicate a way(or 2)in the CU for each outside circuit and put
30mA RCDs directly in the CU (or perhaps RCBOs) and run a ring from
that or do I have to run from a MCB to a 'garage' CU with its own
RCD ?

You could do either.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In article .com,
Sun, 4 Mar 2007 02:45:47 writes

I wish to have a split load CU, with the usual circuits on the RCD side
and lighting/freezer on the other side.

I can never understand the justification of using a single RCD for
all/most of the circuits in a house - other than some saving in costs.

Who in their right mind wants a whole house to go dark just because of a
fault in one area?

I recently was called over to a neighbour where everything had gone off
as the ELCB had detected a fault. In the end it turned out to be the
central heating circuit - probably a faulty immersion heater.

I know that a standard CB is about £5 and a combined CB/ELCB is about
£20 but I would always advocate the use of the latter. For an extra
£100 or so (+ VAT) each circuit could be individually protected for
earth leakage as well as over-current. Considering the total costs
involved in rewiring and the extra cost of the above, I cannot
understand the budget solution even being allowed by the building regs.

If you can, put the fridge and freezer on separate independent circuits
for maximum resilience. If a kitchen appliance develops a fault, your
fridge and freezer will continue working.
--
Les Desser
(The Reply-to address IS valid)

In article ,
Les Desser writes:
In article .com,
Sun, 4 Mar 2007 02:45:47 writes

I wish to have a split load CU, with the usual circuits on the RCD side
and lighting/freezer on the other side.

I can never understand the justification of using a single RCD for
all/most of the circuits in a house - other than some saving in costs.

I agree. In the last 3 houses where I've replaced a CU, I've used
a non-RCD CU, with several RCBOs on the circuits where I want RCD
protection. It's not cheap, but that's what I spend the money on
which I saved by doing it myself.

Who in their right mind wants a whole house to go dark just because of a
fault in one area?

I recently was called over to a neighbour where everything had gone off
as the ELCB had detected a fault. In the end it turned out to be the
central heating circuit - probably a faulty immersion heater.

I know that a standard CB is about £5 and a combined CB/ELCB is about
£20 but I would always advocate the use of the latter. For an extra

None of my CU's have RCBO's available that cheaply.
£25 - £60 is the range I've paid (top end was rather specialised).

£100 or so (+ VAT) each circuit could be individually protected for
earth leakage as well as over-current. Considering the total costs
involved in rewiring and the extra cost of the above, I cannot
understand the budget solution even being allowed by the building regs.

If you can, put the fridge and freezer on separate independent circuits
for maximum resilience.

And central heating and any other frost protection devices.

If a kitchen appliance develops a fault, your
fridge and freezer will continue working.

I usually have two circuits in a kitchen. Non-RCD protected for
stationary and fixed appliances which don't represent a significant
electrocution risk, and RCD-protected for portable appliances and
any other easily accessible socket outlets, which is where the
electrocutionm risk is significant.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 4 Mar 2007 02:45:47 -0800, mused:


In preparation for an extension to my house, I wish to replace my
consumer unit (wired fuse type) with a larger one with spare ways for
the circuits in the extension. The CU replacement will be fairly
straightforward but I have a couple of items I wish to check first.


The power reaches the house by way of a long overhead cable, running
underground from the very last post to our house. Incoming is a fat
black cable which splits to two smaller but still fat cables running
into the company fuse and a henley(?) block.

From these two blocks I have fat red and black cables to the meter,
then same large red & black to a Chilton Current Operated Earth
Leakage Current Detector. Finally cables run from the ELCD to the
Consumer unit. A separate earth cable runs from the CU to an earth
spike. (I will replace this with a much fatter earth cable at the
same time as it looks a little thin to me)

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

Fat black cables? Fat red cables?

Leave it alone, you're scaring me. Time for the Yellow Pages, much
safer.
--
Regards,
Stuart.

Les Desser wrote:

I can never understand the justification of using a single RCD for
all/most of the circuits in a house - other than some saving in costs.

Who in their right mind wants a whole house to go dark just because of a
fault in one area?

Indeed, ("whole house" RCDs) a practice now depreciated

I know that a standard CB is about £5 and a combined CB/ELCB is about
£20 but I would always advocate the use of the latter. For an extra

Typically £40 or more alas. Another issue is that many are two modules
wide (or extra tall and only fit some CUs)

£100 or so (+ VAT) each circuit could be individually protected for
earth leakage as well as over-current. Considering the total costs
involved in rewiring and the extra cost of the above, I cannot
understand the budget solution even being allowed by the building regs.

It isn't permitted in the wiring regs - hence why split load CUs are now
the norm.

If you can, put the fridge and freezer on separate independent circuits
for maximum resilience. If a kitchen appliance develops a fault, your
fridge and freezer will continue working.

Good plan to stick the CH boiler on one as well - save anything freezing
up should you be away on hols. (oh, and tropical fish tanks!)


--
Cheers,

John.

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

wrote:

Don't take this the wrong way, but in common with some of the other
posters, I get the impression from some of your descriptions that you
might want to brush up on some of the finer details before taking on
this job, as there are a number of subtleties that can trap the unprepared!

Might I suggest a copy of the IEE On-Site guide as a basic starting
point? Amazon link:

http://tinyurl.com/32yb6h

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

As Andy suggested two CUs is often a simpler way to do a TT system -
100mA trip RCD in one and 30mA trip in the other. It is often better to
split out outside circuits yet again to save the risk of having them
trip the house circuits. If you are having multiple CUs then a single
master switch positioned before a henley block is a good way to fan out
the meter tails to each CU. That way you still have an overall "off"
switch should it be needed in a hurry.

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

My solution in your situation was to have two CUs for the house, and
then a another dedicated time delayed one for outbuildings (which in
turn have their own RCDs). The outbuildings do not have split load CUs,
but instead have non maintained emergency lighting where appropriate.


--
Cheers,

John.

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

On 5 Mar, 03:23, John Rumm wrote:
wrote:

Don't take this the wrong way, but in common with some of the other
posters, I get the impression from some of your descriptions that you
might want to brush up on some of the finer details before taking on
this job, as there are a number of subtleties that can trap the unprepared!

Might I suggest a copy of the IEE On-Site guide as a basic starting
point? Amazon link:

http://tinyurl.com/32yb6h

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

As Andy suggested two CUs is often a simpler way to do a TT system -
100mA trip RCD in one and 30mA trip in the other. It is often better to
split out outside circuits yet again to save the risk of having them
trip the house circuits. If you are having multiple CUs then a single
master switch positioned before a henley block is a good way to fan out
the meter tails to each CU. That way you still have an overall "off"
switch should it be needed in a hurry.

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

My solution in your situation was to have two CUs for the house, and
then a another dedicated time delayed one for outbuildings (which in
turn have their own RCDs). The outbuildings do not have split load CUs,
but instead have non maintained emergency lighting where appropriate.

--
Cheers,

John.

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

Could I also add in that if the run to the external CU's is lengthy,
then it is desirable to put in another earth rod at that CU. Rods in
parallel will improve the system earthing.

Also before you go upgrading the earth wire, bear in mind that the
earth resistance is quite high and the voltage drop across it will far
exceed that across the earth lead, unless excessively long. If you
search on this NG you will find a method of measuring the earth
resistance - unfortunately I stored the procedure as a .txt file and
can't point you to it. Post back if you can't find it and I will
paste it up.

Rob

In article , John
Rumm Mon, 5 Mar 2007 03:11:59 writes

Typically £40 or more alas. Another issue is that many are two modules
wide (or extra tall and only fit some CUs)

Sorry my memory at fault. £33+VAT at Screwfix for MK

http://www.screwfix.com/app/sfd/cat/pro.jsp?id=38643&ts=90597
--
Les Desser
(The Reply-to address IS valid)

In article ,
Les Desser writes:
In article , John
Rumm Mon, 5 Mar 2007 03:11:59 writes

Typically £40 or more alas. Another issue is that many are two modules
wide (or extra tall and only fit some CUs)

Sorry my memory at fault. £33+VAT at Screwfix for MK

I've got those for £25+VAT each by buying a box of them
from a wholesaler (5 in a box, IIRC).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 5 Mar, 08:55, "robgraham" wrote:
On 5 Mar, 03:23, John Rumm wrote:



wrote:

Don't take this the wrong way, but in common with some of the other
posters, I get the impression from some of your descriptions that you
might want to brush up on some of the finer details before taking on
this job, as there are a number of subtleties that can trap the unprepared!

Might I suggest a copy of the IEE On-Site guide as a basic starting
point? Amazon link:

http://tinyurl.com/32yb6h

I wish to have a split load CU, with the usual circuits on the RCD
side and lighting/freezer on the other side. Is this ok ? and do I
have to leave the ELCD in the circuit or can I connnect the new CU
direct to the meter ?

As Andy suggested two CUs is often a simpler way to do a TT system -
100mA trip RCD in one and 30mA trip in the other. It is often better to
split out outside circuits yet again to save the risk of having them
trip the house circuits. If you are having multiple CUs then a single
master switch positioned before a henley block is a good way to fan out
the meter tails to each CU. That way you still have an overall "off"
switch should it be needed in a hurry.

Finally I want to run separate RCD circuits to the shed (back garden)
and garage (front garden) from the spare ways in the CU. Should these
be on the RCD side or the other ?

My solution in your situation was to have two CUs for the house, and
then a another dedicated time delayed one for outbuildings (which in
turn have their own RCDs). The outbuildings do not have split load CUs,
but instead have non maintained emergency lighting where appropriate.

--
Cheers,

John.

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

Could I also add in that if the run to the external CU's is lengthy,
then it is desirable to put in another earth rod at that CU. Rods in
parallel will improve the system earthing.

Also before you go upgrading the earth wire, bear in mind that the
earth resistance is quite high and the voltage drop across it will far
exceed that across the earth lead, unless excessively long. If you
search on this NG you will find a method of measuring the earth
resistance - unfortunately I stored the procedure as a .txt file and
can't point you to it. Post back if you can't find it and I will
paste it up.

Rob

Rob, I don't quite understand your point about upgrading the earth
wire. I had thought that a larger earth wire and possibly an extra
earth rod would always be a good thing, are you saying that a larger
wire with (presumably) lower resistance would increase tripping of the
RCD or is there a technical problem that I don't understand ?

LHW

wrote:

Rob, I don't quite understand your point about upgrading the earth
wire. I had thought that a larger earth wire and possibly an extra
earth rod would always be a good thing, are you saying that a larger
wire with (presumably) lower resistance would increase tripping of the
RCD or is there a technical problem that I don't understand ?

I think he is saying that the size of wire to the main earth electrode
is not actually that important since it only has a small part to play in
the grand scheme of things.

Say your earth electrode (rod) has a fault loop impedance of 10 ohms
(which is not bad as these things go). A 6mm^2 wire (the size specified
in the in-site guide for TT systems), would introduce a further 6 milli
Ohms/meter extra. So to all intents and purposes the size of the
earthing conductor makes no significant difference to the total earth
fault loop impedance.

Adding additional earth rods *may* help reduce the total earth loop
impedance (if far enough apart), but again that may not be much use
unless you have a very high (or seasonally variable) earth loop
impedance to start with. In the case of an outbuilding it can be
worthwhile making the outbuilding a different TT system from the house -
i.e. its own earth rod etc. You would then need to ensure the CPC of the
submain to the outbuilding is not connected at the destination end.

--
Cheers,

John.

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