Lost cpc at socket

[derbyspark]

Hi i have been working at a 70's prefab bungalow that has no earth reading at 1 socket, it's part of a ring circuit and all readings good end to end from cu r1 0.44 rn o.43 but no end to end on cpc. readings at socket end to end r1 0.44 rn 0.43 but no cpc end to end. have crossed r1 + rn and have proved it to be a ring and no alterations on electrics since built. have checked all cpcs at every socket and all others ok. There's only a 100mm cavity under a ply floor for access. Apparently the houses were bolted together in 2 parts and all electrics were done in the factory, So i am thinking something must be joining them when erected? just seems very strange that readings are so good on L-N but not the earth if there's some sort of loose connection.

 

[supasparxs]

there was a time when ring mains came in, the sparks used to joint the cables in a junction box and only have a radial to the socket.
that maybe the case with your installation, so there maybe a JB somewhere with a loose earth.

 

[derbyspark]

thanks for the reply, never knew that or seen it. There's 2 lives, neutrals and earths at every point and getting crossed linked readings, but somewhere along the the electrics must have been joined together maybe through a jb so food for though.

 

[supasparxs]

maybe not then
apparently, it got so widespread, that an amendment in the regs came in stating that you could had to have more devices than spurs on a circuit, to stop the over use of JB, and spuring off the ring main.

I'm 44 and it was years before I started my apprenticeship

 

[Des 56]

I take it that Zs is apparent at all sockets

If so then possibly the socket with the highest Zs may be the starting point for investigation
It may narrow down your search

By then splitting the ring at that socket and taking the Zs on the other half of the ring,the highest reading on that half may be the linking socket to the other one identified

It may help narrowing down the fault,but if not,it will have served to segregate the two halves for possible conversion to 2 radials


Just editing because the above was a waste of time,I just re read the post and missed that has no earth reading at 1 socket,I'm a muppet

 

[derbyspark]

Yes zs at every socket, Thinking about just running new earth to that that socket as its the main 1 in the living room where the tv is. I'm a little worried that something is likely to be very wrong on connection somewhere tho and will cause problem on L or N in the future.

 

[Des 56]

If there is Zs at every socket,then my post is relevant,thats a relief

The radials option is possibly the one that will remove any concern,You could take a reading of the neutral as well as the R1+R2 for each



Dont you just love ring faults,open any socket and if the fault is on one,it is always the last to be opened (it matters not where you begin)If its under the floor,its the place that is the most awkward to get to,sparks law

 

[supasparxs]

you could run a new earth, but I seem to remember that there is a reg stating that all cables need to be earths
(you know because a DIYer could drill through a cable.)
I would suggest open the ring and test between R1 and Rn,
this way you should find the sockets either side of the socket without the CPC.
Then I would rewire those 2 legs.

anyone else have a view on this one?

 

[derbyspark]

All of the wiring is done below the floor in the cavity and looped up to the socket, but if i replace legs i think it might be hard to disconnect L-N if there is joint boxes somehere, Also had all pipe work was done in a factory and ply put down so with only 100mm cavity it's going to be risky to open up a section.

 

[Octopus]

Draw a sketch map of the bungalow, mark all the sockets on the sketch, do a ZS on all sockets marking the readings on the sketch, and somewhere you'll almost certainly see a significant change in the ZS - then look at these sockets, then check the continuity between them.

Fingers crossed you'll find the area to concentrate on.

 

[ezzzekiel]

if no end to end then theres a break somewhwere, join l/e an test round till you loose continuity

 

[supasparxs]

All of the wiring is done below the floor in the cavity and looped up to the socket, but if i replace legs i think it might be hard to disconnect L-N if there is joint boxes somehere, Also had all pipe work was done in a factory and ply put down so with only 100mm cavity it's going to be risky to open up a section.

what cxable has it been wired in?
is it singles or twin & earth

if the factory made the conduits and cable void, maybe you could draw a new cable in using the old cable as a draw wire.
either using singles, or double insulated singels for the neutral and a single core and earth for the live.
I know you can get this type of cables for lighting however I don't know if you can get it in 2.5mm cable
there maybe a conduit cast in concrete. if so

 

[i=p/u]

do asyou taught at tech.. R1 +R2 at every socket and see where it stops... then go to next socket see if it starts again.... and rub your head walk up and down room , scratch the bald part then go ahhhhhhhhhhhhhhhhhhhh good luck

 

[sparkydude]

As the bungalow is prefab, it sounds very likely that you have a house wired in what they used to call Octoflex, basically a pre-wired conduit system which used to have plug and socket arrangements at junctions between sections of the prefab. It is most likeley that there is a loose pin on a multiplug somewhere, where this may be is anyones guess. If its a bungalow have you looked in the loft ??? Either that or if its wired in conduit , someone has had a brain fart and miswired the ring. My favourite is option 1 though

Nick

 

[derbyspark]

Thanks for the reply's, Bungalow is pitched but there is no loft, ceiling just follows the pitch, new carpets are going in soon so when old ones come will chop some floor up.Might buy a fuse finder to try and track it as there's only 100mm cavity that's insulated so wont be able to see much. Bungalow is wired in t&e.