Investigation of short circuit during rain

Hello, every time it rains, the RCD trips. This means that the garage door, the gate, and the washing machine stop working. The latter problems can only be "fixed" by switching off the fuse for the outdoor lighting. Now, we have numerous outdoor lights. Is there a trick to narrow down the problem so that you don't have to dig up the connections for every single lamp, as the electrician suggests, but can proceed more selectively? Thank you.

Do the outdoor lighting lamps have only fixed connections or also socket outlets? Do individual outdoor lights have their own fuse circuits? I would gradually disconnect everything from the power supply during rain that can be disconnected WITHOUT digging and see if the fault disappears in a certain circuit. Troubleshooting from easy to difficult, not the other way around.

Rain->corrosion/resistance value->earth/moisture… Smells very much like lamps in the outdoor area. Fi monitors L and N. If the outdoor lamps are connected separately, you can narrow down where the fault current flows by disconnecting the neutral conductor at the terminal strip. Caution: Working with electricity is and remains life-threatening! If the specialist already suspects a defective outdoor lamp, I wouldn't experiment. Remove the light bulbs and see when it gets better.

For the brave: Artificially water individual lights with the watering can until the RCD trips.

That already sounds very much like damaged insulation in the soil.

Exactly the same happened to us. We also tried to narrow down the issue by a process of elimination. Without success. Conclusion: no outdoor lighting in the rain anymore. By chance, after 2 years, Bayernwerk AG was looking for a cable fault in an underground cable around the corner from us. Long story short: an electrician found the fault with such a device at our place. It was directly under the pavement of the driveway. The underground cable was damaged. Probably damaged during installation or due to years of stress from the cars.

Often a lamp is also "drowned." I would also try to find the problem spot by pouring water with a watering can. It’s best to seal everything in the outdoor area with Aquasit or something similar. It is reversible and provides peace of mind. Of course, only after a successful test run.