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.

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.

> 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.

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

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

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

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

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.

> 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:

>>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.
> 
> 


No, it's a "proper" kitchen. :-(

Grant

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.

Christian McArdle wrote:

>>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.
> 
> 


Christian, thanks very much for that explanation. The 1.44 ohms figure 
has jogged my memory - last year an engineer came to fix my washing 
machine and he carried out a test on the circuit. He told me that the 
desired figure for a sucessful test was 1.44 ohms but the figure he got 
from my circuit was 3-point-something (I have a note of it at home). he 
told me not to worry because some old houses have values above 30 ohms! 
So it looks like that circuit is already dangerous and I need a rewire.

Thanks again,
Grant

> Christian, thanks very much for that explanation. The 1.44 ohms figure
> has jogged my memory - last year an engineer came to fix my washing
> machine and he carried out a test on the circuit. He told me that the
> desired figure for a sucessful test was 1.44 ohms but the figure he got
> from my circuit was 3-point-something (I have a note of it at home). he
> told me not to worry because some old houses have values above 30 ohms!
> So it looks like that circuit is already dangerous and I need a rewire.


Make sure the sockets are RCD protected. Although the circuit still won't be
up to scratch and would still fail an inspection, this removes the main
potential danger.

Christian.

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.

"Christian McArdle"  wrote in message 
news:4325658b$0$12173$ed9e5944@reading.news.pipex.net...

>> 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.


Thanks, Christian- that's probably the clearest explanation of a fairly 
complicated (to a layman) subject I've ever seen.
    If only my teachers at school could have been like you.........

> 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.

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?

"Christian McArdle"  wrote in message 
news:43257007$0$12185$ed9e5944@reading.news.pipex.net...

>
> Make sure the sockets are RCD protected. Although the circuit still won't 
> be
> up to scratch and would still fail an inspection, this removes the main
> potential danger.


But if it's RCD protected, don't you just need to meet ZsIn <= 50V?  (i.e. 
1667ohm for 30mA)

To me, the regs are clear that it's *preferable* to design for TN systems to 
disconnect on overcurrent rather than RCD, but seem to allow the use of 
RCD's instead.  (413-02-04 (ii) and 413-02-16).

What am I overlooking?

Will

> 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.

> So, I will protect the sockets with an RCD until I get the rewire done.
> Currently there is a 32A MCB for the sockets. Do I simply need to
> replace this MCB with an appropriate RCD or is the RCD in addition to
> the MCB?


If it is an RCD, then it is in addition to the MCB. You could put it in a
separate box after the MCB to just protect the socket circuit.

However, you can get an RCD that replaces an MCB. It is called an RCBO.
However, you may find it difficult to find a suitable device for some older
boards. If you have a DIN rail system, then you should be able to find a
suitable single width RCBO. These are a direct replacement.

Note, that when you get the circuit sorted, you should probably install an
extra few circuits in the kitchen. It is usual these days to have a separate
kitchen ring that is RCD protected and to have one or more circuits for
fixed appliances (washing machines/freezers/fridges/tumble
dryers/dishwashers) that is not RCD protected, so that your frozen sausages
are still frozen when you get back from holiday.

Christian.

"Christian McArdle"  wrote in message 
news:43257920$0$12183$ed9e5944@reading.news.pipex.net...

>
> It comes under bad practice. You could certainly attempt to argue the 
> toss,
> though, if it came to court or something. As I suggested, just adding an 
> RCD
> to the existing system I would regard as sufficiently safe, although much
> over 3 ohms and you're starting to look at lighting and fixed circuits, 
> too.
> However, I would not expect to see such shoddiness in a new or rewired
> installation and would regard such an installation as a cowboy bodge.


But that implies that 413-02-16 is just there for the use of cowboys.

I absolutely agree that one wouldn't design a new circuit like this, but I 
can't see how it would fail a periodic inspection.  It's in compliance with 
the regs and the GN3 guidance.

Of course, it might be a symptom of more serious problems, which *would* be 
failures.


> Best practice is to always design main equipotential bonding and circuit
> cable sizing/resistance for TN-C-S, even on a TT or TN-S system. That way,
> the system can just be transferred to TN-C-S when it becomes available,
> which is increasingly common, even on overhead lines.


Well, it could be anyway, as long as the RCD wasn't removed.

I'm really not arguing with you that it would be a good idea to look at 
what's really happening here, rather than sticking an RCD in and forgetting 
about it - I'm just always interested in what really is compliant and what 
isn't.

Will

> Not so - nothing is recorded, as you say - so even if the cable
> and fittings are date marked, it doesn't matter, as replacement
> of fittings and damaged wiring is allowed without notification.


It would be laughed out of court if you attempted to suggest that your
entire new installation had needed every single fitting and cable replaced
one at a time.

Christian.

> I absolutely agree that one wouldn't design a new circuit like this, but I
> can't see how it would fail a periodic inspection.  It's in compliance
with
> the regs and the GN3 guidance.


I'd expect to see it as an advisory, provided there was appropriate RCD
support and a plastic consumer unit.


> But that implies that 413-02-16 is just there for the use of cowboys.


I suspect it is written like that so that the OP can continue to use his
system (with an RCD) without having the power disconnected by overzealous
contractors/maintenance people. It really isn't that unsafe, provided that
the circuit conductors passed their continuity tests with the expected
numbers.

Christian.

Christian McArdle wrote:

>>Not so - nothing is recorded, as you say - so even if the cable
>>and fittings are date marked, it doesn't matter, as replacement
>>of fittings and damaged wiring is allowed without notification.
> 
> It would be laughed out of court if you attempted to suggest that your
> entire new installation had needed every single fitting and cable replaced
> one at a time.


But in context we're talking about adding a socket to a ring,
which may be exempted anyway!

Christian McArdle wrote:

>>So, I will protect the sockets with an RCD until I get the rewire done.
>>Currently there is a 32A MCB for the sockets. Do I simply need to
>>replace this MCB with an appropriate RCD or is the RCD in addition to
>>the MCB?
> 
> 
> If it is an RCD, then it is in addition to the MCB. You could put it in a
> separate box after the MCB to just protect the socket circuit.
> 
> However, you can get an RCD that replaces an MCB. It is called an RCBO.
> However, you may find it difficult to find a suitable device for some older
> boards. If you have a DIN rail system, then you should be able to find a
> suitable single width RCBO. These are a direct replacement.


I don't know if I have a DIN rail system or not. I think I'll call an 
electrician ASAP and get things sorted once and for all. I am not 
willing to take any risks whatsoever!


> Note, that when you get the circuit sorted, you should probably install an
> extra few circuits in the kitchen. It is usual these days to have a separate
> kitchen ring that is RCD protected and to have one or more circuits for
> fixed appliances (washing machines/freezers/fridges/tumble
> dryers/dishwashers) that is not RCD protected, so that your frozen sausages
> are still frozen when you get back from holiday.
> 
> Christian.
> 
> 


Christian, I can't thank you enough for your excellent advice. I'll 
certainly bear this in mind when discussing my requirements with the 
electrician.

Incidentally, how disruptive is a rewire likely to be? The two public 
rooms and hallway have nicely finished floors and I would prefer not to 
have them damaged. I know it will depend on my installation but will an 
electrician be able to pull through most of the new wiring using the 
existing stuff? None of the socket cabling is plastered in - the sockets 
are either behind skirting or fed via metal conduits.

What about cost? 1000-ish?

Cheers,
Grant

P.S. Anyone know a good electrician in Edinburgh?

"Grant"  wrote in message
news:3okvi4F66bg7U1@individual.net...

> 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

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.

/=================================================================\
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|-----------------------------------------------------------------|
|        John Rumm - john(at)internode(dot)co(dot)uk              |
\=================================================================/

Christian McArdle wrote:


> I suspect it is written like that so that the OP can continue to use his
> system (with an RCD) without having the power disconnected by overzealous
> contractors/maintenance people. It really isn't that unsafe, provided that
> the circuit conductors passed their continuity tests with the expected
> numbers.


Not wishing to alarm Grant any more, but one thing I have not seen 
mentioned yet is performing an insulation resistance check on the 
current circuit either. Since it sounds as if the place is wired with 
"older" cables, that could be a another potential problem area.

-- 
Cheers,

John.

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

> Not wishing to alarm Grant any more, but one thing I have not seen
> mentioned yet is performing an insulation resistance check on the
> current circuit either. Since it sounds as if the place is wired with
> "older" cables, that could be a another potential problem area.


Unlikely, though. PVC is pretty durable.

However, given that only one circuit was used for the entire house, it is
possible that it has been running close to design current at various times,
which may have degraded the insulation more than it might otherwise. Apart
from this, I'd expect PVC installed even 50 years ago to be in serviceable
condition.

Obviously, a periodic test should really involve an insulation test. And it
seems that the entire installation could benefit from one.

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.

Richard Conway  wrote:

> Christian McArdle wrote:
>> The only real chance of problems is if you sell the house and lie on the
>> form
> 
> Or potentially if somebody got injured or worse as a result of the work 
> and an investigation highlighted that the work was done illegally.


Don't they just call you up to investigate and fix the results, and claim 
that it was just a freak accident?

Grant wrote:

>>> My understanding is that any such work now comes under the provisions of
>>> Part P of the Building Regs 
> I'm in Scotland - I think the regs are different here aren't they? Even 
> stricter?


The Regs are completely different and there is no Part P in Scotland.

The Building Standards (Scotland) have always been stricter in that 
electric wiring has always had to be done to a safe and proper standard. 
IEE Wiring Regulations are deemed to be a safe and proper standard, but 
an equivalent is also acceptable.

What will change / has changed is the classes of person who is allowed 
to sign off a certificate. It used to be anyone could sign a 
certificate, now it has to be someone registered. However that only 
applies where a certificate is required i.e. for notifiable work. I 
*think* that wiring is not on its own notifiable and so you don't need a 
certificate. If you were building an extension, which is notifiable, 
then you would need a certificate as part of getting a building warrant.

Unlike English Part P, I don't think council building control officers 
will inspect wiring for you.

The best thing would be to check with Building Control at the local 
council.

Owain

John wrote:

> "Grant"  wrote in message
> news:3okvi4F66bg7U1@individual.net...
> 
>>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_Index/Consumer_Units_Index/Wylex_Std_1/index.html
http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/index.html

or like:

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_NS_Range/index.html
http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Ns_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_Index/Consumer_Units_Index/Wylex_Std_1/index.html
> http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/index.html
> 
> or like:
> 
> http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_NS_Range/index.html
> http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Ns_2/index.html
> 
> 
> Christian.
> 
> 
> 



Hi Christian,

They look like these:

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/index.html

Cheers,
Grant

Owain wrote:

> Grant wrote:
> 
>>>> My understanding is that any such work now comes under the 
>>>> provisions of
>>>> Part P of the Building Regs 
>>
>> I'm in Scotland - I think the regs are different here aren't they? 
>> Even stricter?
> 
> 
> The Regs are completely different and there is no Part P in Scotland.
> 
> The Building Standards (Scotland) have always been stricter in that 
> electric wiring has always had to be done to a safe and proper standard. 
> IEE Wiring Regulations are deemed to be a safe and proper standard, but 
> an equivalent is also acceptable.
> 
> What will change / has changed is the classes of person who is allowed 
> to sign off a certificate. It used to be anyone could sign a 
> certificate, now it has to be someone registered. However that only 
> applies where a certificate is required i.e. for notifiable work. I 
> *think* that wiring is not on its own notifiable and so you don't need a 
> certificate. If you were building an extension, which is notifiable, 
> then you would need a certificate as part of getting a building warrant.
> 
> Unlike English Part P, I don't think council building control officers 
> will inspect wiring for you.
> 
> The best thing would be to check with Building Control at the local 
> council.
> 
> Owain
> 


After having spoken to Edinburgh City Council they tell me that strictly 
speaking I should get a Building Warrant but they have never seen one 
just for adding sockets and wouldn't expect me to apply for one. They 
suggested I get a competent person to so the work for my own piece of mind.

I also asked about mixing old & new cable (different core colours) and 
they said that that was perfectly OK as well. I had thought that I 
needed to add a label to the CU stating that there was a mix but 
apparently not. Maybe just in other parts of the UK?

Cheers,
Grant

Grant wrote:


> I also asked about mixing old & new cable (different core colours) and 
> they said that that was perfectly OK as well. I had thought that I 
> needed to add a label to the CU stating that there was a mix but 
> apparently not. Maybe just in other parts of the UK?


The label is called up in an ammendment to BS7671 - so if you are not 
obliged to work to that then there may be no requirement for it. Having 
said that it sounds like common sense to add it anyway (not as important 
on socket circuits, but makes more difference if you are changing any 
lighting circuits with two way switches, where the three core and earth 
colours could be a tad confusing!)

-- 
Cheers,

John.

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

Grant wrote:
 > After having spoken to Edinburgh City Council they tell me
 > that strictly speaking I should get a Building Warrant but
 > they have never seen one just for adding sockets and
 > wouldn't expect me to apply for one. They suggested I
 > get a competent person to so the work for my own piece of mind.

A pragmatic approach that may seem surprising to those embattled with 
Part Pee.


> I also asked about mixing old & new cable (different core colours) and 
> they said that that was perfectly OK as well. I had thought that I 
> needed to add a label to the CU stating that there was a mix but 
> apparently not. Maybe just in other parts of the UK?


The requirement for the warning label is part of the IEE regulations. If 
you're following the IEE regulations, you need the label.

However the Building Standards (Scotland) do not require the label, 
merely an equivalent level of safety.

Labels are cheap.

Owain

> They look like these:
>
>

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/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/BH40slash2slash30.html

Installed in one of these:

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

Christian.

Christian McArdle wrote:

>>They look like these:
>>
>>
> 
> http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Wylex_Standard_Range/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/BH40slash2slash30.html
> 
> Installed in one of these:
> 
> http://www.tlc-direct.co.uk/Products/BHCT2.html
> 
> Christian.
> 
> 


Christian,

Many thanks (again!) for the information.

Cheers,
Grant