Adding a new ring with one wire?

[fabgav]

hi all,

current the house is on one main ring both upstairs and downstairs.
adding new sockets upstairs so want to split the two to have 2 ring mains
the trouble is i can only get one feed wire from CU upstairs as the CU is in the corner of living room which is fully decortated so i'm not ripping it down now lol

My question is, Can i have one wire from CU on a RCD procected MCB going upto one socket on 2.5mm wire with a lenght of no more thant 2 metres
then can i make a ring from the 1st socket and loop it around all the other new sockets and back to the 1st socket thus creating a ring upstairs from a CU fed socket.

does that make sense?

 

[Paul_C]

Sorry, but that would not be acceptable. You would have a single 2.5 sq. mm. cable feeding the entire ring which is not rated to carry the maximum current which it could be called upon to carry.

You'd be better to look at splitting the upstairs into separate radial circuits on 20A MCB's.

 

[Steve]

It is possible to serve a ring final with only one cable, but it must be 4mm² or above (basically rated more than 32A).

Given this is the upstairs sockets, why not make it a 20A radial? This would be acceptable.

 

[fabgav]

are radial's okay to have then because there are going to be about 6 sockets over two rooms? if i do this then will i need 4 mm cable for the entire radial circuit?

 

[ban-all-sheds]

It is possible to serve a ring final with only one cable

Possible, yes.

Compliant with the Wiring Regulations, no, not unless you used that cable to supply a CU where the ring final could start.

 

[electronicsuk]

It is possible to serve a ring final with only one cable

Possible, yes.

Compliant with the Wiring Regulations, no, not unless you used that cable to supply a CU where the ring final could start.

I know it's been discussed before, and it certainly isn't a standard circuit configuration, although I can't remember anyone ever coming up with anything concrete from BS7671 that would either explicitly forbid or allow it.

IIRC the only assumption was that since the ring final is an exceptional circuit configuration, it should not be modified beyond the standard circuit design in any way.

In any case, it would be confusing to say the least should anyone need to inspect/test the installation in the future!

 

[Steve]

are radial's okay to have then because there are going to be about 6 sockets over two rooms?

Yes its fine. Radials are good for where a ring final is inconvenient.

if i do this then will i need 4 mm cable for the entire radial circuit?

No. A radial can be run in 2.5mm² but it must be protected by a 16 or 20 amp MCB, because a 2.5mm² can only carry 27 amps MAXIMUM. A circuit must use the same cable throughout usually, unless there is some fusing down at the point of change.

16 amps is usually plenty for upstairs sockets, especially only 6 sockets (or 12 if doubles). Bedrooms are low-use rooms (alarm clocks, lamps, a computer, tvs). Unless you have electric heaters!

 

[dingbat]

Anybody - 'electrician' or not - installing ring final circuits needs to think again about committing that particular electrical design offence.

Ring final circuits were an ill-considered solution to a problem that did not actually exist. Furthermore, this pointless 'solution' was proposed in the mid 1940s and all the supposed reasons (which were not actually solved by installing rings) have long since gone away.

The only reason 'electricians' install ring final circuits is because they've always done it. Sixty-odd years on, it's about time they stopped.

(That way, in another seventy or so years time, we might finally fall into line with the rest of the civilised world, in this one respect at least.)

 

[Taylortwocities]

Hoorah! Dingbat for President!!!

 

[electronicsuk]

The only reason 'electricians' install ring final circuits is because they've always done it. Sixty-odd years on, it's about time they stopped.

I think it is very condescending to infer that professional electricians should not be installing a ring final circuit, which is just as much an accepted form of circuit design as the radial.

Like anything, the ring final has its place. Critics often point out that a broken leg on the circuit can lead to a fire risk. I would ask those same critics how often they have actually come across such a situation, when in terms of maximum current carrying capacity for 2.5mmsq conductors, the overload (even on a fully utilised ring) would be minor. Furthermore, how is this any better/worse than the pitfall of a broken CPC on a radial circuit?

Personally, I think it's about time people got off their high horse about it. If you wish to be ignorant of a tried, tested, accepted and regulated manner of circuit design, that's your choice. However, with the ever increasing requirement for RCD protection and, hence, RCBOs becoming more commonplace, you might want to reconsider - unless you have deep pockets, that is.

 

[RF Lighting]

Hoorah! electronicsuk for President!!!

 

[Steve]

boooo hissssss

 

[electronicsuk]

Hoorah! electronicsuk for President!!!

To be fair, that was only because I hinted at the use of RCBOs

 

[RF Lighting]

I'm also a fan of RFCs.

I know they are certainly not a one fits all soloution for every socket circuit, but I definatly would prefer to have the option to install one where it is suitable.

 

[fabgav]

okaaaaaaay, so i'm lost now with all this stuff lol

So, the 2.5mm cable i've managed to squeez up a pipe in the wall can go on a 20A mcb and can then go on a radial circuit to all my sockets and it should all be fine yes?

Thanks everyone