No earth at socket

[jwphillips]

MCB tripped due to minor roof leak causing water to dribble down thru roof felt and onto external aspect of plasterboard in attic conversion. Water came into contact with back of double socket. Isolated system and disconnnected 2.5mm T&E supplying socket. Double socket appears on ring main supplying attic conversion as they were 2 leads. I have connected up 2 loose ends into 30A junction box to make safe, whilst roof leak fixed.

Meantime used simple socket tester to test double sockets around room and opened number of sockets to check wiring. Hollow fast fix type plastic mounts with no flybacks needed are in use. 3 double sockets in one corner appear to have no earth according to socket tester, whilst most do. On the opposite corner there appears to be one double socket with no earth. Most appear to be on the ring with one on an apparent "spur".

I don't have equipment or knowledge to start testing earth loop impedence, etc.. I'm not certain how this could have happened. Could it relate to the roof leak have caused some burning in the wires at the original double socket.

Your advice would be welcome before I call out a spark.

Thanks

 

[Steve]

Its essential that you do not use any of the sockets until you have established the earth issue. Even the screws on the faceplates could become live if a fault occured.

Anyway, did you open up any other sockets?

The socket you opened, did that have earth wires connected?

You need to open up the sockets and check for earth wires being connected, then go downstairs and find where the ring has been extended from (IF it has been extended - you may find the whole lot is one long spur - again, do not use it if this is the case)

 

[jwphillips]

I opened several sockets. 2 had the 2 earth wires covered in g and e sleeve but twisted together and not connected to 1 of the 2 earth terminals. Reconnecting appropriately did not make any difference. I can't tell whether 3 of the no earth sockets are on a long spur or part of a true ring main. My understanding was that you should only have 1 socket per spur?

Looks like I need a PIR?

 

[Steve]

I opened several sockets. 2 had the 2 earth wires covered in g and e sleeve but twisted together and not connected to 1 of the 2 earth terminals.

If you mean they were both connected to ONE terminal, this is ok, as long as its the one on the socket itself, not the backbox.

I can't tell whether 3 of the no earth sockets are on a long spur or part of a true ring main. My understanding was that you should only have 1 socket per spur?

True, but if its been DIY'd, or the builder's "electrician mate" did it, anything's possible. The one-socket-per-spur rule is because 2.5mm² T+E is only rated to 25 amps or so. a twin socket can only draw 13 amps without being overloaded.

Looks like I need a PIR?

Possibly, but it may be possible for you to fix this yourself. If you open up all your sockets upstairs, and check every one, you will be able to tell where all the wires go and whether, in fact, you have an extended ring, or a long spur! A long spur is correctable by putting a fused spur in line, to limit the whole lot to 13 amps.

 

[jwphillips]

Have opened up all of the faulty sockets with no earth. 3 of them had satisfactory wiring. In 2 the earth wire had become disconnected. Re-connected the earth wir made no difference to the socket tester result. All 5 have no satisfactory earth reading. 2 sockets are on opposite faces of an internal partition wall. Both have 2 cables present. The other 3 sockets are on the opposite side of the room. The central socket has 2 cables, but the other 2 have 1 cable each.

How would adding a FCU solve the lack of earth at these sockets?

 

[sparkyspike]

It won't.

You either have TWO breaks in the CPC on the ring, or ONE break in a spurred radial circuit.

You need to locate the breaks before trying to correct the spur situation (if there is one).

You will need a multimeter with a continuity setting to trace the fault. Quite a simple task - can take a while though, especially if the break isn't at a socket (it could be in an inaccessible JB!). Using a continuity meter will at least show you roughly where the problem is.

 

[Steve]

How would adding a FCU solve the lack of earth at these sockets?

It wouldn't, but it would be a solution to having loads of sockets on a spur. You can have as many sockets as you want protected by a 13 amp fuse!

Anyway, back to the earthing.

When was the loft converted? Who did the electrics?

If you cannot answer these questions, then get an electrician in.

 

[jwphillips]

Further developments. Crawled around in roof space around attic conversion. Appears to be a radial circuit, but without multimeter guess could be long spur. All seemed OK until I discovered 2.5mm T+E disappearing into space above alcove with 1.5 3 core and earth appearing on other side. There is a plastic chock with blue wired to black, red wired to red and yellow wired to bare earth with no G+E sleeve. The bare earth from the 3 core is not connected. I a resolved to call out electrician to further investigate. I don't know whether they ran out of 2.5 T+E and used a short section of 3 core, but that's not satisfactory. It would be possible to extend from another socket on the other side of the room, but I don't know whether this is ring, radial or spur. Presumably the 3 core and earth shouldn't be taking loads from anything other than lighting? I won't use these sockets until checked further.