Radial Power Circuits - Upgrading

[buildersmate]

One for Bright Spark or another qualified person.
If a dwelling has been rewired 30 years ago from its original (1920s) radial configuration, not converted to ring circuits for power sockets, is there an obligation to convert to rings when upgrading the CU to MCBs plus RCD.
Research suggests radial circuits can be acceptable under 17th Edition?

[LCDMAN]

Radials fine provided correct rating breaker is used - 20A for a radial, rather than 32A for a ring. UK are about the only ring users left in the world....

[buildersmate]

Thanks LCDMAN. Just what I wanted.

[Old_Geezer]

Really ? That surprises me. Surely it uses more cable to radial every socket ? Would have thought in this environmental conscious age they'd all be gradually changing to ring main.

[LCDMAN]

OG, you misunderstand radials. Several sockets on each radial "leg" - but no return to CU - so less cable used but less current capacity. Your image is more like the old network "star" topology - 1 radial leg = 1 socket/node. Not how it's done.

[LCDMAN]

http://www.tlc-direct.co.uk/Book/6.3.3.htm

[Old_Geezer]

Ah ok. Maybe I don't tend to think of them like that because I don't see an advantage. I'll read the book.

[BRIGHT SPARK]

BM..radials have several advantages over rings
You can wire 2 radials using almost as much cable as 1 ring
If one radial trips you still have the other
Instead of having a 32a current rating(as on a ring)you will now have a total of 40a (2 x 20)
You could wire the radials in 4mm cable giving you a 32a capacity on each radial.
Testing is simplified with radial circuits also.

[buildersmate]

BS, thank you for the additional clarification. The dwelling in question is already wired as a radial in PVC, replacing the original rubber insulation cable. What I don't want to have to do is rewire again when the CU is upgraded, and was wanting to check the Regs. I'll check, but I think the existing is 2.5mm squared cable, as the existing cartridge fuses are 15A. Assume that one fits a 16A MCB on each radial circuit.
I'm also clear the work needs Part P Building Regs.

[BRIGHT SPARK]

Without going too deep into the regs,there is a requirement that the radial circuits cannot serve more than a certain m2 of floor space.However in most domestic situations the breach would be unlikely.You should be ok with a 20a 'b' type mcb....though I would use BS 61009 RCBO units for each circuit as these will give full overcurrent and earth leakage protection to each circuit separately .....(they are becoming cheaper).