3/036 t and e on domestic ring final

If it's flat twin and earth cable, the cpc may be a problem if you split into 2 no. radials on B16 - dependent on the installation's prospective fault current vs let-through of the mcb. (usually the cpc for 3/036 is slightly under 1 sq mm). Similar problem to that with circuits wired in the later 1970s T&E that had 2.5/1.0.

Would be good to know what else you've seen that might be leading towards C2?

Are there any signs of overload? (Or have you already assessed predicted load is likely to lead to short-term small overload?) To be honest, that would be my biggest worry, especially if it's supporting a number of rooms (or a single room likely to have heavy current-using appliances).

Other than that, it would appear (on the surface ... but of course you may know something not apparent to us in the Forum), it may be safer to leave it as a ring final circuit on a B16, than split it? Yes, it's not a "conventional circuit", but from a volt-drop and overload protection perspective, as well as adiabatic for cpc (or line conductor for L-N) in parallel would be better?

what sort of fuse/breaker or rcbo is it on, and does the cable show signs of thermal distress?

a modern rcbo will speed disconnection to a point that will to a  degree mitigate the risk of insulation damage in an earth fault. If overload is the concern, then derate the breaker in the  ratio of the expected cross-section to what you have, so perhaps 1.9/2.5 changes 32A to 25A or less.

Unless  you need to break the ring for other reasons I'd agree with Graham, retain the ring, it is more flexible in terms of load distribution  and safer with the redundant earth paths, and saves you a breaker position at the board.

Mike

Thanks for the replies so far.The circuit is on a dual rcd board.So if no sign of overloading,the circuit could attract a C3 or no code at all?

                     Hz

Quite possibly. You might make take a more stringent view if it's rented property, or change of use (tenant may not know or care about the possibility of overload, or new owner/occupier may not be aware), but if it's an owner-occupied property, and the owner is aware of the situation, it's far less likely to be accidentally overloaded if serving a number of rooms.

Apparently 3/.036 was commonly used for immersion heater circuits. Did we every find a damaged earthing continuity conductor?

https://www.diynot.com/diy/threads/imperial-cable.214429/#:~:text=As%20per%20the%20table%2C%203%2F.036%20had%20a%201%2F.044,inbuilt%20core%20must%20be%20very%20rare%20Not%20especially.

Don't be shy chaps - pros will know...

3/0.029" x 1/0.044" (cpc 0.98mm²)
3/0.036" x 1/0.044" (cpc 0.98mm²)

7/0.029" x 3/0.036" (cpc 1.97mm²)

7/0.036" x 7/0.029" (cpc 2.98mm²)

7/0.044" x 7/0.036" (cpc 4.59mm²)

7/0.052" x 7/0.044" (cpc 6.86mm²)

7/0.064" x 7/0.052" (cpc 9.59mm²)

Apart from final two, have measured real cable with trusty Moore & Wright.
-0-

Z.

On conducting a condition report the rf was found to be wired in 3/036 on a b16 mcb.

If it's wired as a ring on a 16A OPD, I'd be happy if the CCC if the cable was above 10.72A  (0.67x In) - so no problem with 3/.036 on that score in most situations (provided the ring wasn't ridiculously unbalanced).

c.p.c. size for fault protection might be an issue in theory - but hardly any worse on paper than 1.0/1.0 T&E on a B6 MCB, which seems to be thought acceptable whatever the numbers in BS EN 60898 might say. With knowledge of the actual PEFC you might be able to show that the 40ms disconnection time for the RCCB would be sufficient to protect it anyway.

I don't see any advantage in breaking the ring into radials if keeping the same OPD rating - just disadvantages in terms of v.d. and loss of duplicate earthing.

You can't condemn something on an EICR just because it doesn't match something in the OSG - you need to dig a lot deeper than that.

   - Andy.