In article ,
"Christian McArdle" writes:
Ring circuits were designed to be easily constructed by converting
from 15A radial circuits, originally.

Yes, I'd forgotten about those! They usually have both ends of the ring
going to different MCBs...

MCB's would be rather unlikely, but originally, they could both go
to separate 15A fuses when such a conversion was done, these being
the fuses which originally protected the two 15A radial circuits
which were converted into the two ends of the ring.

--
Andrew Gabriel