RCD trips intermitenly

Hi,

We had a new extension build 1.5 years ago and this is where the problem is so new cables etc.

We first had the RCD tripping with the light circuits downstairs but then it went away and never happened again. 2-3 months ago we had the RCD trip with the downstairs sockets. I isolated the issue with the Fridge and it kept tripping but after 4-5 hours then just started working again. I have a simple plug tester with the 3 dots and all plugs appeared to be fine.

Today same thing happened again. This time turning off the Fridge (we also have a Fridge main switch, chunky switch) didn't help. It kept tripping. In the meantime i tried to isolate the issue, but turning off different kitchen appliances but to no avail. Every time it will trip and could not isolate the issue to a particular device or socket. Then after 3-4 hours it started working again, no issues now.

Does anyone have any ideas what might be causing it? My builder doesn't want to know basically. Thank you!

RCD's Tripping are normally caused by a Damp issue getting into the wiring and producing an Earth leakage current somewhere on a circuit or poor insulation. In the first instance i'd start to look at any sockets/lights that have water near them.

If you only have one RCD serving all of the circuits, isolating via MCB's might or might not stop the RCD tripping. In other words a circuit can still trip an RCD, even if the circuit is turned off.

The reason being that the fault could be on the neutral, which isolating at the MCB does not disconnect.

As simple as I can explain it, RCD sense the level of current in live versus neutral, any imbalance and they should trip. Imbalance means some current is taking a path other than the path the are suppose to take - live, through load, to neutral. The alternative path, will be via earth. Idea is it could be YOU forming that connection to earth, from a live pole, so it trips to protect you or the installation.

As mentioned above, it could be damp, it could be an oven element failing, could be a nail through a cable making intermittent contact. Sometimes trips can be caused by the mains filters on equipment, or several items of equipment.

As above, do you have any outside lights / sockets?

Harry Bloomfield said:

If you only have one RCD serving all of the circuits, isolating via MCB's might or might not stop the RCD tripping. In other words a circuit can still trip an RCD, even if the circuit is turned off.

The reason being that the fault could be on the neutral, which isolating at the MCB does not disconnect.

As simple as I can explain it, RCD sense the level of current in live versus neutral, any imbalance and they should trip. Imbalance means some current is taking a path other than the path the are suppose to take - live, through load, to neutral. The alternative path, will be via earth. Idea is it could be YOU forming that connection to earth, from a live pole, so it trips to protect you or the installation.

As mentioned above, it could be damp, it could be an oven element failing, could be a nail through a cable making intermittent contact. Sometimes trips can be caused by the mains filters on equipment, or several items of equipment.

Click to expand...

Hi thank you both. See pic attached, so there are 2 RCD. The second line points to the switch that's tripping. So when i lift the black switch then the RCD trips. As long as no 2 switch stays down the rest of the circuits are fine and no issues with electricity. There is a external socket outside, properly done, IP44 socket which should be water proof. But how come, it was the fridge before and this time it didn't seem to play a role. Can the outside plug cause the rest of the problems. Can an electrician discover where the fault might be, you mentioned a nail going through a cable (unlikely) but can the electrician figure this out? So it cannot be an overload of the circuit, by some design fault which is causing this from what you are saying, it should be some water interference? Thank you again.

crystal ball said:

As above, do you have any outside lights / sockets?

Click to expand...

yes there is, just replied. When i used the socket tester the external socket didn't show any issues but it doesn't mean it's ok? I will check this first thing this weekend and see if there any signs of corrosion. Thanks

Using that switch may not be isolating the fridge circuit fully. Unplug the fridge to be certain it isn't the appliance.

NB. When I needed to do that many years ago, pulling out the appliance revealled all an an interesting cause of my trips.