RCD tripping randomly after electrical work

[Micramary]

We have been in our house for a few months. We had a full electrical inspection done and an earthing rod was put in. We then had the overhead power cables put underground, so the meter was relocated into white box on outside of garage, not too far from where it had been inside the garage. An electrician then put tails from fuse board/ box inside garage to meter outside and connected us back up.
Since then the RCD trips about once a day, with nothing prompting it. It never tripped before the work. When I asked the electrician he said it was likely leakage from appliances, but we haven't changed anything - it is the same as before the relocation of cables etc. the only change is underground cabling, meter box moved and tails from electrician. Any ideas? Thanks.

 

[securespark]

A diary may prove helpful.

Try and disconnect stuff as much as possible. Either switch off, if it has a switch (like boiler, shower, cooker, immersion heater etcetera) or unplug altogether if it plugs in.

Leave it for a few hours (if you can) with everything disconnected. Does it still trip?

If it does not trip, plug back in or switch on the bare essentials, burglar alarm, fridge, freezer and boiler. Use other things by all means, but unplug them (or switch them off) when they are done with.

Has the guy who reconnected you left any paperwork?

Did he get the polarity right?

Did he test the RCD to check it is operating within the correct parameters?

 

[ricicle]

If you never had an RCD before or one not as sensitive, then the fault(s) on the wiring or appliance(s) may have already been there but the RCD is now highlighting the fault(s) for you.
Have you always had the RCD ? If so it is quite possible that you never had a sufficient earth path to operate it before.

 

[Micramary]

Always had RCD - the whole fuse box is fairly new. Had whole system, plugs etc checked couple of months ago when they put in new earthing rod. There was no tripping until last week when the tails were put in, cables underground and meter moved. If it was appliances wouldn't we have experienced tripping before. Unfortunately the electrician didn't leave paperwork, he was brought in by our builder. I'dlike him to come back to check but am not sure what I need to ask him. Starting with RCD parameters sounds good.

 

[securespark]

Can you post a piccy of where the new cable connects to meter and before the meter?

 

[Micramary]

Will have a go! The meter is now in a white box on the outside wall and the fuse box on inside of garage. I will take a pic and try to load it!

 

[Micramary]

Images as requested - thanks. View media item 60495 View media item 60494 View media item 60493The fuse box photo is upside down for some reason and where the tails go to the meter outside is sideways!

 

[ericmark]

I can't read from pictures but I would think 30ma type? Clearly two is it just one that is tripping? I would think from your report that there was a problem with earths in the past or you would not have fitted an earth rod. So the fault could have been there for years but without the earth rod would not have tripped anything. RCD's are not all the same some will resist tripping without real faults better than others. But first step is to find if real fault or some spike on the line. If always same one likely real fault. There are some odd faults but one a day first I would look to fridge/freezer switching on auto defrost so would try moving so supplied from other RCD.

Extension lead and move items one at a time from one RCD to other most likely method to isolate what is wrong.

 

[Micramary]

Ok thanks. The earth road has been in for 3 months with no tripping. Only since meter moved and tails have we had tripping. One thing that I just noticed is that the electrician has put all switches to on whereas a couple were off before as they were not needed. I will put those to off to see if that makes a difference, then try the elimination process.
Yes there are two, and only one is tripping. It did it during the night last time so if it is an appliance then I suppose that points to fridge or freezer?

 

[pjcomp]

How old are fridge and freezer - they're vey good at setting off RCDs when they get old.

PJ

 

[Micramary]

Freezer is about eight years old, fridge the same. The freezer would be my first elimination, but it hasn't been causing trips before this work was done. Could this work have made the RCD more sensitive?

 

[ban-all-sheds]

Only since meter moved and tails have we had tripping.

Only since the meter moved etc have you had what appears to be a TN-C-S supply.

With a much lower resistance to earth any leakage currents will increase.

 

[JohnW2]

[nly since the meter moved etc have you had what appears to be a TN-C-S supply. With a much lower resistance to earth any leakage currents will increase.

True - but the leakage currents (in the range we're talking about) would only increase by a tiny amount ... imagine that there had been a 29mA leakage current when he had a TT supply - total leakage path impedance about 7,930Ω at 230V, say 7,830Ω plus 100Ω TT electrode resistance.

Now let the Ze decrease to near zero, due to change to TN-C-S - leakage path now ~7,830Ω, leakage current ~29.4mA at 230V.

The change from TT to TN-C-S is, in itself, most unlikely to have made the difference between a leakage not tripping and tripping an RCD.

Kind Regards, John

 

[ban-all-sheds]

You're only saying that because you bothered to do the calculations.

 

[JohnW2]

You're only saying that because you bothered to do the calculations.

I only did some real calculations because I realised what the answer would be. I knew that the leakage loop impedance had to be around 8kΩ at the 30mA trip threshold, and hence realised that the TT's 100Ω or so was really a pretty trivial proportion of that!

Kind Regards, John