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I have recently bought a house and it came with this panel (from what I could gather, it was renewed sometime in the past 10 years):

enter image description here

Today, I changed a light switch and afterwards I had the main circuit breaker (#33 - #36) trip twice, completely randomly. It completely bypassed the other breakers and tripped the main one directly.

To work on the light switch, I shut down breaker #8 and then went downstairs to paint another room (without turning #8 back on). There was virtually no load on the whole circuit - the only things plugged in were a freezer and a 50W LED lamp, each on its own separate circuit, with their separate breakers.

I am curious what might have caused this and how I can avoid it in the future. Location is Germany

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  • You changed a light switch and problem started. Would say something not done right with the light switch. Would bet a ground(metal box) is too close to a bare hot(screw head).
    – crip659
    Oct 14, 2021 at 20:58
  • I also thought of the possibility, but does this still apply even though I never started the breaker after installing the new switch? Installation is pretty stupid proof, you just stick the cables in their designated place (see 360 here: elektro-wandelt.de/Berker-3036-Aus-Wechselschalter.html), so it might that the switch itself is broken
    – kioleanu
    Oct 14, 2021 at 21:10
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    Your main 33-36 breaker looks like an RCD/ECLB/GFCI (not sure which terminology is used in Germany). If it's tripping with no load on then it's possible you've accidentally shorted Neutral and Earth/Ground somewhere with your recent work on that light switch.
    – brhans
    Oct 14, 2021 at 21:58
  • Tripping a breaker usually means a hot to ground connection. Would still double check the switch since that is when problem started.
    – crip659
    Oct 14, 2021 at 22:00
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    @crip659 That doesn't look like a regular breaker (and not even a main one, i bet that's the triple at the bottom right). I'd agree with brhans, had a similar thing happen after plugging in an old portable light, and eventually found that it had ground and neutral bonded in the plug.
    – Dan Mašek
    Oct 14, 2021 at 22:52

1 Answer 1

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You tripped the RCD

RCD is British for GFCI. I'm not sure if there's a separate German phrase for that.

Standard European practice is to have a "whole house RCD" protecting the entire house. This is normally right before, or right after, the main circuit breaker. However it is also common for the RCD to be combined with the main circuit breaker.

What is an RCD/GFCI? A better question is "how does electricity flow?" It flows in loops. Electricity goes out one wire, and comes back another wire. And the currents in both wires are always equal and opposite, since it's a loop. So what is an RCD? It is a device which monitors current flow on neutral and all hot wires. It wants to see that the sum of the currents (counting for direction) is exactly equal. i.e. cancel each other out.

Once all the normal currents cancel, what is left? Residual current. That means current going one direction, and disappearing / coming back ??? not through the normal wires. ??? Arcing to earth??? Shocking a human ???

So the RCD trips when that happens.

Since your light switch wiring is what changed, 99% chance your light switch wiring contains (or contained) the fault.

One thing that will get you is "smart switches" (especially cheap Chinese) that need neutral to power themselves. And the old switch wiring is a "switch loop" with no neutral. So the temptation is to wire the switch neutral to safety earthing. Now the switch's own power comes out the hot and returns on earth. Earth bypasses the RCD, so the RCD correctly sees it as residual current/ground fault. (ground=earth).

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  • Thank you for the great explanation. I think that is exactly what happened. The problem didn't manifest itself anymore after I turned the #8 breaker on. Can this indicate a fault with the panel?
    – kioleanu
    Oct 15, 2021 at 12:07

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