RCD tripping randomly after electrical work

[securespark]

Sure it's TN-C-S?

 

[plugwash]

JohnW2's calculations of course assume that the previous TT system actually had a functional earth rod.

 

[securespark]

The earth conductor that follows the tails does not look like it connects to the cut-out.

The earth conductor we can see connected to it disappears.

If it was TT before, unless PME was requested, it is highly likely the DNO reinstated what was there before.

After all, why would the spark bother with a rod if there was going to be a PME upgrade?

 

[JohnW2]

JohnW2's calculations of course assume that the previous TT system actually had a functional earth rod.

They do, indeed. However, the OP seems very clear in saying that the TT rod was installed, by an electrician, a couple of months ago, without any trips occurring, and it's only since the meter/cutout move/changes (and possible change to TN) that the trips started occurring. I took this to indicate that there was almost certainly a 'functional earth rod' in place during that period when no trips were occurring - although I may, of course, be wrong!

Of course, the reality is that many TT installations (mine being an extreme example) will have a lower impedance path from MET to earth due to bonding of extraneous-c-ps than would be provided by a TT electrode, even if the TT electrode is not 'functional' (or is disconnected!).

Kind Regards, John

 

[Micramary]

To clarify: we had an earth rod put in on advice of electrician. It now seems we didn't need that if we were going underground. We do have pme but kept earth rod as guy said would do no harm and can never have too much earthing! No tripping after rid, only tripping since moving of cables, meter and tails. Thanks so much for all your input

 

[JohnW2]

The earth conductor that follows the tails does not look like it connects to the cut-out. The earth conductor we can see connected to it disappears.

It does look that that. However, the G/Y from the cutout must go somewhere. Indeed, if it isn't being used as the earth, then it probably qualifies as an extraneous-c-p and ought to be bonded! [That would actually create a rather odd situation, since that 'bonding' would effectively mean that it was being used as the installation's earth!]

If it was TT before, unless PME was requested, it is highly likely the DNO reinstated what was there before.

Possibly true, but I've quite often heard of people being 'offered' PME when such work has been done. It certainly happened to most people in my village when the supply was PMEd and (for most of the village, not me)the supply was moved from overhead to underground.

After all, why would the spark bother with a rod if there was going to be a PME upgrade?

I suppose he may well not have known. The work to cutout/meter was apparently done as a result of DNO changing from overhead to underground supply, not work requested by the OP, so it could be that, at the time, neither OP nor electrician knew that the work was going to happen.

Kind Regards, John

 

[securespark]

The fact that only one RCD trips suggests to me that maybe there is a fault on that side of the board.

Have you isolated stuff to see if you can eliminate anything?

 

[Micramary]

I am starting the process of elimination...problem is things like freezer, as the tripping seems to only happen once a day/ every other day! Will start with others as use up freezer contents, then go for that last.

 

[EFLImpudence]

Will start with others as use up freezer contents, then go for that last.

You don't need to do that.

As said, supply one item by an extension lead from a socket on the other RCD and carry on as normal.


If the original RCD still trips then it's not that item.

 

[JohnW2]

I am starting the process of elimination...problem is things like freezer, as the tripping seems to only happen once a day/ every other day! Will start with others as use up freezer contents, then go for that last.

As Eric suggested early on, one way of dealing with 'difficult' things like the freezer would be to use a long extension lead to power it from one of the circuits (maybe an upstairs sockets circuit) which is protected by the other RCD. If the freezer is the culprit (at least, the lone culprit), then that ought to result in the other RCD tripping, in due course.

[I presume from what you've said that it is always the same RCD which trips?]

Edit: I must take some speed-typing lessons At least we're giving consistent advice!

Kind Regards, John