Weird RCD trips

[silverdiy]

About 6 years ago we had the consumer unit replaced with a modern version containing MCBs and an RCD on the power circuits.
Earlier this year the RCD tripped, I reset it immediately and put it down to 'this is what you get with modern stuff'. Then it tripped again, perhaps a month or so later. I reset it and thought I'd better keep an eye on this. Since then, it trips approximately every month but can always be reset immediately on the occasions when I've noticed it straight away. Sometimes it's tripped in the middle of the night when only a few appliances are in operation, mainly fridges (2) and freezer.
The electrician who updated the system came in and did loads of tests, found no faults and went away just suggesting I try to isolate faulty appliance.
Now, my reasoning is that because it trips quite regularly (once a month) it must be something that works on some sort of time sequence. The only thing I can think of is the auto defrost on the fridges, although from what I've read, auto defrost happens more often than once a month. I'd tend to rule out anything connected with water leakage since it's always possible to reset the RCD pretty much straight away whereas the effect of water would surely persist longer. It's a transient of some sort, something switching?
Any thoughts on this mystery would be appreciated. Apart from the nuisance (and possible loss of freezer and fridge contents if we're away when it trips) I just hate not being to find an explanation for things ...
Thanks
Silver

 

[securespark]

Did he do an insulation test on the RCD protected circuits?

Have you got a copy of the results?

If he has thoroughly ruled out the wiring, the best thing to do is to have the bare minimum of stuff connected permanently:

Burglar Alarm

Boiler

Fridge

Freezer


The rest you plug in or switch on when you use it, then unplug when finished.

It's a fag, but if you only have a handful of things connected, then if it trips, you know it has to be one of them.

 

[Iggifer]

presumably your consumer unit only has one RCD not two? Are all circuits protected by this RCD or are there some unprotected ways?

 

[silverdiy]

securespark
He did an insulation test on the protected circuits. I haven't got the results, I didn't notice him writing anything down, I assume he just made a mental note that everything was OK/within spec.
Iggifer
There is only one RCD in the CU and this protects 3 rings circuits. Lighting and the cooker are unprotected.

I still think thee's some sort of clue in the facts that the RCD can be reset successfully almost immediately. Plus the fairly regular trips every month - sometimes in the day and sometimes in the night.

 

[ericmark]

All RCD's are not the same the write up for X-pole makes this plain. So there are a number of ways forward from better quality RCD to use of RCBO's so splitting the circuits.

My RCD's do trip from time to time and have done since I fitted them in around 1992 clearly that old not to the standards of a modern one although still 30ma. I find I tend to get a batch of tripping then a time with no tripping which could as easy be spikes on the supply as fault with my house.

It is common when resetting one for the other to trip with spike caused. I have planned to change my two fuse boxes and two RCD's for a modern consumer unit with either X-Pole or RCBO's for many years but just not got around to it.

The problem with RCBO's is one can trip without one noticing it. There is no 100% answer.

 

[Iggifer]

The problem with RCBO's is one can trip without one noticing it. There is no 100% answer.

Agreed but the OP doesn't have any circuits (he's told us about) that would go unnoticed for a long period of time.

5/6 ccts wouldnt cost much for an all RCBO board, but for one trip / month I wouldn't be too concerned

 

[EFLImpudence]

I still think thee's some sort of clue in the facts that the RCD can be reset successfully almost immediately.

I agree. It would appear to be an appliance switching.

Plus the fairly regular trips every month - sometimes in the day and sometimes in the night.

In the night would seem to narrow it down to Fridge, Freezer, Heating etc.

An RCD fault is very difficult to find as it can be an accumulation of lesser faults adding up to enough current to trip the device.

Other than moving one socket circuit at a time (and waiting) to the non RCD side finding the fault will be down to luck or extensive testing.

 

[silverdiy]

Reasons for wanting to sort this are:
1. possible loss of freezer and fridge contents when we're out for more than half a day. Plus nuisance of the alarm kicking in.
2. if my wife is left alone - temp or permanently ( - she just won't be able to cope with it !!
I spoke to the electrician about RCBOs and apart from their cost, he says that because they are bigger than MCBs, some rework of the wiring in the CU wouil be needed.
Looks like I'm in for a long haul process of trying to eliminate appliances one at a time ..... ?