Final ring circuits with radial CPC

[bwm730]

Have justed looked at a job to replace the consumer unit and it appears that both the final ring circuits ( Kitchen and the rest of the Flat ) have Radial CPC's. The flat is wired in multicore Singles and Plastic Conduit , has anyone come across this type of design before. Both "ring circuits" are currently on 32A MCB's , Singles appear to be 2.5mm and CPC is 1.5mm. Did a quick continuity test and LL and NN meter out fine and all sockets have a good Earth . There is no way of adding the return CPC ( concrete floors and ceiling ), what are my options? Thanks

 

[Octopus]

I'd drop all the sockets and try and see which ones lead to the fuse board. And rewire from the board till to you can meet the earth coming the other way. If your just missing 1 return earth leg then this shouldn't be to hard.

Usually a bit of pulling on cables can establish where they go.

I love rewiring these flats 2 of you can have one buttoned in 6-7 hours.

If all else fails you'll have to go surface

Why drop the sockets. Do a Zs at each and see where the difference is the greatest and you should find the missing "link" there, or there abouts

 

[Deleted member 26818]

Unfortunately Engineer, it would appear that electrical work is now becoming a paint by numbers trade.
Just look at the EICR schedule of inspections.
We have Part P and just about any Tom Dick or Harry now calling themselves 'qualified', the OSG, which is quite usefull for charts, such conduit spacings etc. but does seem to offer a one size fits all solution, which many appear to see as being gospel.
We now have BS7671 providing information for standard circuits in Appendix 15 which many now see as the only why to wire a circuit, when in fact, it's there to explain to these Toms, Dicks and Harrys just what a RFC is.
There's all these new Regulations popping up unexpectedly, most not even necessary, and some that contradict existing Regulations.

 

[Deleted member 26818]

No requirement in BS7671 for a ring to have RCD protection?? There is if a socket is used by unskilled or likely to be used outdoors, or if the Zs tolerance of the CPD is exceeded which may be the case if the cpc is broken. Or is it i have totally misinterpreted the regs all these years lol.

No the requirement is to provide protection for the socket-outlet not to the circuit.
No Zs should not be exceeded if BS7671 is complied with.
In such circumstances where for whatever reason Zs are not satisfactory, 30mA RCD protection is only one of the available options
A time delayed 100mA, 300mA or even 500mA RCD could be used, or the preferred method of supplementary bonding installed.
It's quite a common misconception that socket circuits require 30mA RCD protection, rather than the sockets, so don't beat yourself up over it.

 

[rattlehead85]

Yes spinlondon you are quite correct in saying it is the socket itself rather than the circuit. Point i am trying to make is that the circuit the o.p is talking about is most probably RCD protected in any case so his situation does not incur immediate danger. I am sure if it was a choice between fitting an RCD to a circuit origin or change every outlet for an RCD socket i know what 99.9% of customers would want you to do.
I couldn't agree more these regs are so contradictive and misguiding they create more questions than provide clear answers.
The industry really needs to review these publications and guides and provide one clear and precise document.

 

[Robert Turnbull]

Why drop the sockets. Do a Zs at each and see where the difference is the greatest and you should find the missing "link" there, or there abouts

I ment to drop them to establish the tube run to the board ( tug test ) which if your good may only be one. you then may have to drop more to rewire the earth to the point needs to get to.

and obviously the one you need to connect to will need to be opened to make the connection.