Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead is
the fact that the existing cable appears to be ever so slightly thicker
than the 2.5mm^2 that I was going to use. It is also multi(6)-stranded
instead of single-stranded. Is this to be expected with older wiring (I
believe a rewiring was done in the 70's)? There is a 32A MCB at the fuse
box so I thought that 2.5mm^2 would do the job but having seen the
existing wire I now have doubts. I don't want to weaken the installation
by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in
the room and they both still worked - does this allow me to conclude
that I have a ring mains? Also, 4mm^2 cable doesn't seem to be available
from B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!

Cheers,
Grant

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in the
room and they both still worked - does this allow me to conclude that I
have a ring mains? Also, 4mm^2 cable doesn't seem to be available from
B&Q, etc. - the next size up is 6mm^2.

Maybe it was a radial at some point, then was taken back to the CU and made
into a ring?

Are there any markings on the cable?

Sparks...

Sparks wrote:
After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in the
room and they both still worked - does this allow me to conclude that I
have a ring mains? Also, 4mm^2 cable doesn't seem to be available from
B&Q, etc. - the next size up is 6mm^2.


Maybe it was a radial at some point, then was taken back to the CU and made
into a ring?

Are there any markings on the cable?

Sparks...



No markings on the cable. What I have noticed is that some of the
existing cable doesn't appear to be copper - it is a silvery colour.

Cheers,
Grant

Grant wrote:
Sparks wrote:
After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets
in the room and they both still worked - does this allow me to
conclude that I have a ring mains? Also, 4mm^2 cable doesn't seem to
be available from B&Q, etc. - the next size up is 6mm^2.

Maybe it was a radial at some point, then was taken back to the CU and
made into a ring?

Are there any markings on the cable?

.... and can you see both ends of the ring coming back to the C.U.?


No markings on the cable. What I have noticed is that some of the
existing cable doesn't appear to be copper - it is a silvery colour.

It's tinned copper.

Chris Bacon wrote:
Grant wrote:

Sparks wrote:

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets
in the room and they both still worked - does this allow me to
conclude that I have a ring mains? Also, 4mm^2 cable doesn't seem to
be available from B&Q, etc. - the next size up is 6mm^2.


Maybe it was a radial at some point, then was taken back to the CU
and made into a ring?

Are there any markings on the cable?


... and can you see both ends of the ring coming back to the C.U.?


I don't really know what I'm looking for at the CU so I think, based on
other advice in this thread, I should really be getting in a qualified
electrician.

Cheers,
Grant

No markings on the cable. What I have noticed is that some of the
existing cable doesn't appear to be copper - it is a silvery colour.

Probably tinned standed cable, as used yonks ago. You can probably use the
2.5mm cable as you wish. However, you should be doing a full circuit test
afterwards, which will ascertain that the circuit is a complete ring.

If it really is a radial (which is unlikely), your choices are to use bigger
cable, or drop the MCB to 20A, which is no hardship if the circuit just
covers a few reception or bedrooms. Don't even think about it for a kitchen,
though.

However, if you're unlucky the test may show that the old cable isn't up to
the earth loop impedence test. In that case, you probably must drop to 20A,
or even rewire.

You'll need an electrician to do the testing. It is probably well beyond
your experience, and the test equipment costs many hundreds of pounds.

Christian.

Christian McArdle wrote:
No markings on the cable. What I have noticed is that some of the
existing cable doesn't appear to be copper - it is a silvery colour.


Probably tinned standed cable, as used yonks ago. You can probably use the
2.5mm cable as you wish. However, you should be doing a full circuit test
afterwards, which will ascertain that the circuit is a complete ring.

If it really is a radial (which is unlikely), your choices are to use bigger
cable, or drop the MCB to 20A, which is no hardship if the circuit just
covers a few reception or bedrooms. Don't even think about it for a kitchen,
though.

However, if you're unlucky the test may show that the old cable isn't up to
the earth loop impedence test. In that case, you probably must drop to 20A,
or even rewire.

You'll need an electrician to do the testing. It is probably well beyond
your experience, and the test equipment costs many hundreds of pounds.

Christian.



Many thanks for your reply. I think it's time for a professional!

Cheers,
Grant

Christian McArdle wrote:
If it really is a radial (which is unlikely), your choices are to use bigger
cable, or drop the MCB to 20A, which is no hardship if the circuit just
covers a few reception or bedrooms. Don't even think about it for a kitchen,
though.

Flipping the 32A MCB off shows that all sockets in the house (dining
room, sitting room, hall, 3 bedrooms & kitchen) are all on the same circuit.

Cheers,
Grant

Flipping the 32A MCB off shows that all sockets in the house (dining
room, sitting room, hall, 3 bedrooms & kitchen) are all on the same
circuit.

Ouch. You should really look into splitting the kitchen off it, unless it is
a tiny kitchenette.

Christian.

In an earlier contribution to this discussion,
Grant wrote:

Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead
is the fact that the existing cable appears to be ever so slightly
thicker than the 2.5mm^2 that I was going to use. It is also
multi(6)-stranded instead of single-stranded. Is this to be expected
with older wiring (I believe a rewiring was done in the 70's)? There
is a 32A MCB at the fuse box so I thought that 2.5mm^2 would do the
job but having seen the existing wire I now have doubts. I don't want
to weaken the installation by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in
the room and they both still worked - does this allow me to conclude
that I have a ring mains? Also, 4mm^2 cable doesn't seem to be
available from B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!

Cheers,
Grant

2.5mm^2 is fine for a ring main as long as you *insert* it into the ring so
as to still have a continuous ring - rather than creating spurs. My house
has a mixture of older (stranded) cable and new solid stuff. Doesn't seem to
be a problem!

There is a limit (can't remember what it is!) to the permitted number of
outlets on a single ring - but you probably won't exceed that unless the
ring has already been extended.

My understanding is that any such work now comes under the provisions of
Part P of the Building Regs - and that, legally, the work needs to be
certified by a qualified electrician - or by Building Control if they are
capable! Many competent DIY-ers choose to ignore this - particularly if
there's no obvious evidence as to *when* the work was carried out.

But if you're not confident *and* competent, get an electrician.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Set Square wrote:
My understanding is that any such work now comes under the provisions of
Part P of the Building Regs - and that, legally, the work needs to be
certified by a qualified electrician - or by Building Control if they are
capable! Many competent DIY-ers choose to ignore this - particularly if
there's no obvious evidence as to *when* the work was carried out.

Effectively, it doesn't matter when it was done, as long as there
isn't an exact record existing of what's there.

Chris Bacon wrote:
Set Square wrote:

My understanding is that any such work now comes under the provisions of
Part P of the Building Regs - and that, legally, the work needs to be
certified by a qualified electrician - or by Building Control if they are
capable! Many competent DIY-ers choose to ignore this - particularly if
there's no obvious evidence as to *when* the work was carried out.


Effectively, it doesn't matter when it was done, as long as there
isn't an exact record existing of what's there.

I'm in Scotland - I think the regs are different here aren't they? Even
stricter?

Cheers,
Grant

In an earlier contribution to this discussion,
Chris Bacon wrote:

Set Square wrote:
My understanding is that any such work now comes under the
provisions of Part P of the Building Regs - and that, legally, the
work needs to be certified by a qualified electrician - or by
Building Control if they are capable! Many competent DIY-ers choose
to ignore this - particularly if there's no obvious evidence as to
*when* the work was carried out.

Effectively, it doesn't matter when it was done, as long as there
isn't an exact record existing of what's there.

Well, on the basis of complying with the 11th commandment "Be thou not found
out" - it's as well to make sure that there's no incriminating evidence
which could prove that the work was done *after* the introduction of Part P.
This could be important if and when you want to sell the house.

For example, if the electrics are in an extension which was built this year,
they *couldn't* have been done before Part P.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

For example, if the electrics are in an extension which was built this
year,
they *couldn't* have been done before Part P.

And date stamps on cable etc. are becoming more common.

Christian.

Christian McArdle wrote:
For example, if the electrics are in an extension which was built
this year, they *couldn't* have been done before Part P.

And date stamps on cable etc. are becoming more common.

Readers will have to refer to previous messages in this thread
for context. Why not quote a bit more?

Anyway:

Even if date stamps are on *everything*, then what does it
matter if there's no previous record of what was installed?

Set Square wrote:
Chris Bacon wrote:
Set Square wrote:
My understanding is that any such work now comes under the
provisions of Part P of the Building Regs - and that, legally, the
work needs to be certified by a qualified electrician - or by
Building Control if they are capable! Many competent DIY-ers choose
to ignore this - particularly if there's no obvious evidence as to
*when* the work was carried out.

Effectively, it doesn't matter when it was done, as long as there
isn't an exact record existing of what's there.

Well, on the basis of complying with the 11th commandment "Be thou not found
out" - it's as well to make sure that there's no incriminating evidence
which could prove that the work was done *after* the introduction of Part P.
This could be important if and when you want to sell the house.

For example, if the electrics are in an extension which was built this year,
they *couldn't* have been done before Part P.

There's the existing record, then - however, I shall be very interested
if anyone knows what information is collected - is it simply "electrics
passed", or is it "electrics passed, CU (type xxx), socket on wall X, Y,
Z; lighting to points a,b,c (type xxx) (etc., etc.)". What is recorded?

There's the existing record, then - however, I shall be very interested
if anyone knows what information is collected - is it simply "electrics
passed", or is it "electrics passed, CU (type xxx), socket on wall X, Y,
Z; lighting to points a,b,c (type xxx) (etc., etc.)". What is recorded?

Bugger all. Your chance of being detected is between zero and nil.

The only real chance of problems is if you sell the house and lie on the
form, with would be regarded as fraud and could end you in prison. Your new
house owner will be far more motivated at picking up infringements and
evidence of new work than a BCO who is more interested in his next job where
he gets to say how deep the foundations go.

Christian.

Set Square wrote:

There is a limit (can't remember what it is!) to the permitted number of
outlets on a single ring - but you probably won't exceed that unless the
ring has already been extended.

The limit is actually based on maximum floor area (100m^2) served by the
circuit, rather than a number of sockets as such. However, while this
should not be exceeded, you should still design the circuit taking into
account likely loads. So in a kitchen you may decide that a ring of only
10m^2 is "full"

My understanding is that any such work now comes under the provisions of
Part P of the Building Regs - and that, legally, the work needs to be
certified by a qualified electrician - or by Building Control if they are
capable! Many competent DIY-ers choose to ignore this - particularly if
there's no obvious evidence as to *when* the work was carried out.

Adding a socket to an existing circuit counts as a "minor work" IIRC and
hence is not notifiable.

--
Cheers,

John.

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

Grant wrote:
Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead is
the fact that the existing cable appears to be ever so slightly thicker
than the 2.5mm^2 that I was going to use. It is also multi(6)-stranded
instead of single-stranded. Is this to be expected with older wiring (I
believe a rewiring was done in the 70's)? There is a 32A MCB at the fuse
box so I thought that 2.5mm^2 would do the job but having seen the
existing wire I now have doubts. I don't want to weaken the installation
by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in
the room and they both still worked - does this allow me to conclude
that I have a ring mains? Also, 4mm^2 cable doesn't seem to be available
from B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!

Cheers,
Grant

Grant,
if it has 7 cores then it may be the old 7/029 standard. 7 cores,
0.29 something, and more tricky to work with than 2.5mm. 2.5mm came in
about the late 60s/ early 70s iirc. Yes it looks like a ring, yes I'd
just extend it with 2.5mm.
Phil

P.R.Brady wrote:

Grant,
if it has 7 cores then it may be the old 7/029 standard. 7 cores,
0.29 something, and more tricky to work with than 2.5mm. 2.5mm came in
about the late 60s/ early 70s iirc. Yes it looks like a ring, yes I'd
just extend it with 2.5mm.
Phil


I'm pretty sure that it has six cores, but I'll check when I get home
tonight. However, based on other advice in the thread regarding full
circuit & earth loop impedence tests I think I will hand this job over
to a professional.

Cheers,
Grant

I'm pretty sure that it has six cores, but I'll check when I get home
tonight. However, based on other advice in the thread regarding full
circuit & earth loop impedence tests I think I will hand this job over
to a professional.

Note that there is no harm in running the cables before they come. That's
the long, expensive laborious bit, and I would say that there was an 80%
chance of the cabling being useful.

You only need the electrician for the skilled bit involving expensive
equipment.

Christian.

Christian McArdle wrote:
I'm pretty sure that it has six cores, but I'll check when I get home
tonight. However, based on other advice in the thread regarding full
circuit & earth loop impedence tests I think I will hand this job over
to a professional.


Note that there is no harm in running the cables before they come. That's
the long, expensive laborious bit, and I would say that there was an 80%
chance of the cabling being useful.

You only need the electrician for the skilled bit involving expensive
equipment.

Christian.



Yes, I was planning on doing that. I am now having nighmares about my
house being ripped apart for a rewire (especially after having had the
floors done). Not enough forward planning I suppose :-(

Out of interest, maybe you could enlighten me on what a failed earth
loop impedence test would signify and what dangers does it put me at
risk from?

Cheers,
Grant

Out of interest, maybe you could enlighten me on what a failed earth
loop impedence test would signify and what dangers does it put me at
risk from?

When you have an earth to live fault, in the worst case, the current has to
flow from your incoming supply, through the consumer unit, along the circuit
cables to the furthest point. It then has to flow back down the earth
conductor back to your incoming supply. The incoming supply will also have
some resistance along its live and earth connection.

The earth loop impedence is the total of all the resistances of the path
that the current has to flow down.

Now, a socket circuit must disconnect rapidly in the event of a fault. Using
MCBs, to trip quickly enough, you must be able to guarantee that the current
flowing will be 5 times the circuit rating. Therefore, a 32A circuit needs
160A to reliably flow. That requires a total earth loop impedence of 230/160
= 1.44 ohms, some of which will already come from the supply.

Now, the old cables you have found, I believe, had a smaller earth conductor
than modern cables. The horrendously large ring, including your entire house
has more of it, too. It is quite possible that the resistance of the cable
will be too much, either as is, or with your proposed extension.

The danger of not fixing this potential problem is that in the event of an
earth fault, it could take tens of seconds to disconnect the power, which is
a fire and electrocution risk.

In reality, such circuits are normally RCD protected, so provided the RCD is
present and working, then the danger is not real, although it is not
permitted to design circuits that rely on this, with the exception of TT
earthed (earth rod) systems, where it is simply not possible to comply.

Christian.

P. R. Brady dropped a zero in his message. He was correct at first with
7/029 as the name but that is seven strands of 0.029 of an inch or 29
thousandths of an inch.

Chris.

"Grant" wrote in message
...
Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead is
the fact that the existing cable appears to be ever so slightly thicker
than the 2.5mm^2 that I was going to use. It is also multi(6)-stranded
instead of single-stranded. Is this to be expected with older wiring (I
believe a rewiring was done in the 70's)? There is a 32A MCB at the fuse
box so I thought that 2.5mm^2 would do the job but having seen the
existing wire I now have doubts. I don't want to weaken the installation
by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in the
room and they both still worked - does this allow me to conclude that I
have a ring mains? Also, 4mm^2 cable doesn't seem to be available from
B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!


It sounds like 7/.029 cable which was the forerunner of 2.5 solid conductor
and ws usually tinned copper conductors.
A simple solution of just using 2.5mm T&E to extend it is possible but
ignores the ramifications of cicuit protective conductor sizing (earth
conductor) and fault currents. However I suspect most of the run of the mill
sparkys might do just that.
4mm cable is readily available from half decent suppliers and some
wholesalers might even be willing to cut lengths for you.
For a fuller answer we would need to know what earthing arrangements apply
to your installation and an idea of possible cable lengths involved. You
have already advised us that you have a 32A MCB but can you tell us if it a
type B or otherwise? If the protection is problematic it might be possible
to use a 32A RCBO but we need answers first

John wrote:
"Grant" wrote in message
...

Hi,

I want to extend the ring mains in my (1930's) house to add two double
sockets to a room. I've got the floorboards up and know where the new
cable needs to go. However, the thing that's stopping me going ahead is
the fact that the existing cable appears to be ever so slightly thicker
than the 2.5mm^2 that I was going to use. It is also multi(6)-stranded
instead of single-stranded. Is this to be expected with older wiring (I
believe a rewiring was done in the 70's)? There is a 32A MCB at the fuse
box so I thought that 2.5mm^2 would do the job but having seen the
existing wire I now have doubts. I don't want to weaken the installation
by using wire that is too thin.

After a bit of Googling it seems that 4mm^2 cable might be used in a
radial installation but I disconnected the wire between two sockets in the
room and they both still worked - does this allow me to conclude that I
have a ring mains? Also, 4mm^2 cable doesn't seem to be available from
B&Q, etc. - the next size up is 6mm^2.

Maybe the fact that I'm having to ask these questions suggests that I
should get in an electrician?!



It sounds like 7/.029 cable which was the forerunner of 2.5 solid conductor
and ws usually tinned copper conductors.
A simple solution of just using 2.5mm T&E to extend it is possible but
ignores the ramifications of cicuit protective conductor sizing (earth
conductor) and fault currents. However I suspect most of the run of the mill
sparkys might do just that.
4mm cable is readily available from half decent suppliers and some
wholesalers might even be willing to cut lengths for you.
For a fuller answer we would need to know what earthing arrangements apply
to your installation and an idea of possible cable lengths involved. You
have already advised us that you have a 32A MCB but can you tell us if it a
type B or otherwise? If the protection is problematic it might be possible
to use a 32A RCBO but we need answers first



Hi,

I have checked the old wire, and yes, it has seven conductors in it (I
had previously indicated that I thought it had six).

I plan to replace 3 metres of the existing wire (there isn't very much
slack between the two sockets it currently joins) and add another length
across the room (2 metres) to a new socket. Then another 3 metres to
another socket, finally completing the ring with existing cable which I
will cut about 1.5 metres off.

The 32A MCB has "Type 2" written on it and the CU is an old brown
plastic Wylex one (other MCBs in the CU have "Type B" written on them).
Can I get an RCBO for this or is a new CU required?

Cheers,
Grant

The 32A MCB has "Type 2" written on it and the CU is an old brown
plastic Wylex one (other MCBs in the CU have "Type B" written on them).
Can I get an RCBO for this or is a new CU required?

Do they look like:

http://www.tlc-direct.co.uk/Main_Ind...d_1/index.html
http://www.tlc-direct.co.uk/Main_Ind...nge/index.html

or like:

http://www.tlc-direct.co.uk/Main_Ind...nge/index.html
http://www.tlc-direct.co.uk/Main_Ind...s_2/index.html


Christian.

Christian McArdle wrote:
The 32A MCB has "Type 2" written on it and the CU is an old brown
plastic Wylex one (other MCBs in the CU have "Type B" written on them).
Can I get an RCBO for this or is a new CU required?


Do they look like:

http://www.tlc-direct.co.uk/Main_Ind...d_1/index.html
http://www.tlc-direct.co.uk/Main_Ind...nge/index.html

or like:

http://www.tlc-direct.co.uk/Main_Ind...nge/index.html
http://www.tlc-direct.co.uk/Main_Ind...s_2/index.html


Christian.





Hi Christian,

They look like these:

http://www.tlc-direct.co.uk/Main_Ind...nge/index.html

Cheers,
Grant

They look like these:


http://www.tlc-direct.co.uk/Main_Ind...nge/index.html

OK, to my knowledge, you won't find an RCBO to fit that. You'll need a
standalone RCD installed after the existing MCB.

Something like:

http://www.tlc-direct.co.uk/Products...h2slash30.html

Installed in one of these:

http://www.tlc-direct.co.uk/Products/BHCT2.html

Christian.