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? 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.

(For various reasons, he is keen to rewire with as little disruption as
possible and is happy to accept the limted numbers of sockets etc he
currently has - so being able to reuse the conduit drops to the sockets
would be ideal, but they are only large enough for one cable, unless the
circuit is wired in singles and conduit added everywhere).



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.

However a look at the general state of the wiring leads us to suspect
that it could probably do with a rewire PDQ. So I thought it prudent to
do some tests on it.

There are three/four [1] circuits in total, connected to to three
rewireable fuses. All the cable is rubber or PBJ insulated (inner and
outer), unearthed on the lighting circuit. Separate steel earth wire on
an ex-cooker point radial (this was the one that was disconnected), and
T&E construction on the ring circuit cable.

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.

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.


[1] The lighting circuit seems to have two cables terminating at the CU.
There is an open circuit between them, leading to the conclusion there
may in fact be two separate circuits (12 light fittings - so that would
also suggest more than one). For some reason however they are terminated
on one fuse, in spite of there being three spare ways in the CU complete
with unused 5A fuses!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/