In article ,
John Rumm writes:

Looking at a mates ring circuit wiring, the original builder (1950's
bungalow) has wired the only ring final circuit up from the CU into the
loft space, done a lap of the loft and then back to the CU. At each
socket position there is a junction box, which takes off a single 2.5mm
sq unfused spur and drops it down a conduit to the socket 5' away.

The question is, is this style of wiring still permissible?

Yes.

It violates
the guideline of having no more spurs per circuit than there are actual
outlets directly on it, but I can't find anything in the regs that
explicitly forbids it.

The reason behind that is that rings normally have no spurs when
initially installed, and are extended with spurs. When you get to
the point where it's doubled in size with added spurs, then it's
time to reevaluate the adiquacy of the original design.

Given that this ring was not installed that way, then you need to
use your own judgement to decide if it's time to consider if the
ring is too big and needs splitting or has been hacked around so
much that it could do with reinstalling.

Background for those that are interested:

Got a call from my friend the other day to say that he just had a new
washing machine delivered, and his house nearly managed to electrocute
the delivery bod! Anyway we traced the problem to a disconnected earth
on the socket in question, capacitive filters on the appliance input,
and earthed pipes. Anyway we fixed that easy enough.

One issue with that would be you can't get two connections to each
socket for separate earth paths, not that this is required for just
a washing machine in any case.

The Earth fault loop impedance was actually not bad considering (no
worse than 0.25 ohm in most places, rising to 0.7 on the end of several
cascaded 4 way trailing leads!). TN-S supply.

That's one reason why extension cords are bad things, and daisy
chaining extension cords and/or multi-way socket blocks is a very
bad thing.

Insulation resistance on the lighting and ex-cooker point circuit was
also ok at 200M Ohm @ 500V (surprisingly!). The ring circuit however
was another matter. The best isolation between any pair of conductors
being 40K ohms! The (inner) cable insulation was visibly disintegrating
and would fall off if the wire was bent about much.

Rubber when it was in good condition actually has a higher insulation
resistance than PVC.

--
Andrew Gabriel