Nothing went in my favour today.

[Goody]

Went to replace a rewirable fuse board and had a real nightmare with upstairs ring.

Continuity of the conductors are OK but when tested for IR, there was a dead short between earth & neutral.

1. Opened up all sockets but couldn’t see any problem.
2. Tried splitting the ring – with one end (that gives a good IR) connected to the MCB, I get no supply (weird) and when I tried the other end, the other RCD trips.

I got to go back tomorrow; any feedback would be much appreciated.

Cheers!

 

[robsparky1975]

Looks like you may need to split the ring up some more im afraid,you just dont know what people have added on down the years(diyers)hopefully you get to the source sooner rather than later,going to have to go form cu to each leg of ring and so on.

 

[Marvo]

I got to go back tomorrow; any feedback would be much appreciated.

Cheers!

You do realise tomorrow is Sunday?

 

[Goody]

You do realise tomorrow is Sunday?

No peace for the wicked, I guess!

 

[hermetic]

Earth wire in neutral terminal at the back of a socket? socket front screw piercing a cable?, If you are on PME it would still work, and not trip the rcd as neutral and eart potentials are (should be) the same.I would take all the sockets offand check the connections behind them first before you get too involved in head scratching. Most faults turn out to be simple in the end!

 

[JD6400]

I think you are going to have to go down the 1/2 , 1/4 route but keep a eye on the socket fronts , i have seen more than couple go down over time , even had new ones with Ir faults !

 

[micknew]

If you have just replaced the board you have probably shared the ring main supply between the 2 RCD's.

 

[Goody]

If you have just replaced the board you have probably shared the ring main supply between the 2 RCD's.

I paired up the legs by checking the continuity and I don't think that's an issue. I now beginning to suspect a shared neutral. I think I really got into a hell hole as all the rooms are with laminated flooring and the sockets don't reveal anything.

 

[Goody]

... Most faults turn out to be simple in the end!

Very reassuring, thanks! I should live in hope.

 

[spark 68]

If you are on PME it would still work, and not trip the rcd as neutral and eart potentials are (should be) the same.

Of course this would trip the RCD!, as they are effectively joined together before the RCD, they should never meet again or they will trip the RCD

 

[Engineer54]

Of course this would trip the RCD!, as they are effectively joined together before the RCD, they should never meet again or they will trip the RCD

Was just about to point the same thing out myself!! lol!!!

 

[mogga]

"shared neutral"???? causing a neutral to earth fault WTF??

 

[telectrix]

suppose it could if someone had borrowed a N from another circuit and that N was down to E.

 

[hermetic]

what about the bond link in the DNO cutout, they are at the same potential throughout the installation, rcd will not trip.

 

[spark 68]

what about the bond link in the DNO cutout, they are at the same potential throughout the installation, rcd will not trip.

Of course it will trip,

An RCD works by monitoring what current is flowing through the RCD on the line side, and the same current returning through the RCD on the neutral side, these should be equal but opposite thus cancelling each other out = no trip.

If the current returns via the CPC, it is effectively bypassing the RCD, leading to an imbalance which = trip.

You would in effect be shorting out the sense coil on the Neutral side.
The PD doesn't really come into it.