Who can work out this one!!

[brizospark]

Ok here is a fault I discovered today which is a bit of a headscratcher

Was called to a house today to look at problem with upstairs sockets, the customer was saying that they were working intermittently

so first thing I did was get the volt stick out for a quick check. There was one socket which had laptop etc plugged in and I noticed the volt stick was glowing whenever I went near any of the equipment let along te plug top or cables. Thought at first it may be interference with the
volt stick as I know they are unreliable for this.

Anyway looked properly into this problem there are 5 sockets on a ring. First socket from DB I plugged in my socket tester everything ok. Went to the second socket and live earth reversed showed up! Ok that explains why volt stick was glowing away from cables and plug top. So I opened socket number 2 expecting to find a simple live earth reverse but everything was ok. Opened all other sockets and these appeared ok

so I split the ring and pinpointed the problem to be between socket 2 and 3. Could not trace cable as the cable was concealed within walls etc. it was at this point I noticed tat the boiler too was fed from this circuit, but only had 1 cable at FCU. there was not three cables at any socket so I am assuming that they have cut into cable between socket 2 and 3 and mixed up live and earth!!! Cannot access this joint though as under hard wood floor!!

so in the end I disconnected the link between socket 2 and three and split the ring into 2 x radials at the DB , both protected by a 16 a mcb and rcd. I also had to put a plug top on the boiler and plug it into socket 2 temporarily. This has cleared the fault

heres the bits I cannot fathom, entire house rcd protected. Why did this fault not trip the rcd and also why was the polarity not showing up as incorrect at socket1???

 

[RJT_94]

did you conduct any other tests? ir or any rcd tests?

 

[ste77]

did u test the RCD just cos its there doesnt mean it works properly

 

[Rockingit]

1) Have you considered that the polarity reversal may be on the outgoing side of socket one?
2) When you understand how an RCD works you will understand why it doesn't give a monkies about polarity (normally)
3) And more importantly to your client - a polarity reversal is unlikely to be causing intermittent results. Suggest you go looking for a loose connection once you've found the reversal.

 

[ste77]

Also you need to carry out ring continuity on the circuit as you may have had two radial circuits on the 32A mcb

 

[dcelectrical]

also just cos the rcd is fitted doesnt mean its connected, seen loads of them bridged out cos they kept tripping

 

[brizospark]

The rcd is connected and is tripping out within the permitted times on rcd tests

 

[brizospark]

Plus at socket 2 I tested

l-n 0v
l-cpc 230 v
n-cpc 230v

this indicates te the 230v is at the cpc. What would cause this?

 

[Rockingit]

Plus at socket 2 I tested

l-n 0v
l-cpc 230 v
n-cpc 230v

this indicates te the 230v is at the cpc. What would cause this?

The polarity reversal that you're looking for!!!!!!!!!!!!!!!!!!!!!!!!

 

[Lrmurray]

live and earth is reversed. that is why you are getting those readings

 

[mark80]

Could be simply a loose neutral in the joint box to this socket! No neutral = no potential difference between live and neutral. Neutral basically becomes live. thats why you are getting readings between L-E and N-E.
If it was the case of wrong polarity then the socket would never have worked! Deff sounds like a loose neutral to me, especially with the intermittent issues

 

[Deleted member 9648]

^^^^11 posts in problem nailed methinks^^^^
Easily checked as there will only be a voltage on the neutral if a load is connected on the broken side....also suggests the circuit is not a ring.

 

[Guest111]

The circuit cannot be a ring,in the situation you describe if we assume that it is wired correctly in cu then if the L and E conductors had been crossed somewhere then in effect you would have a direct short to earth unless they had been crossed twice.