I’ve always been a bit disappointed that the US never adopted RCD’s at the service panel. I discovered a double-gang light switch box at my house that for some inexplicable reason has a common neutral for lights on two separate circuits, and when replacing one after turning off what should have been the correct breaker I got a nice buzz touching the neutral wire - if the panel had an RCD those lights never would have worked in the first place.

In hindsight it was stupid to not have turned off both circuits anyway, I’m just glad I was wearing sneakers so the shortest path to ground was the junction box itself.

Using a shared neutral for two circuits was a common practice to save on wire. It's allowed as long as the two circuits are connected to different legs/phases of the electrical panel.

More recent versions of the NEC require that the breakers used for both hot legs of such circuits be linked so turning one circuit off also turns off the other.

Common neutrals on residential branch circuits have largely fallen out of favor for new construction due to requirements for GFCI or AFCI protection on most circuits.

For anyone as unfamiliar with the term RCD as I was until now, it is the same thing that in the US we typically call a GFCI or GFI (ground-fault circuit interrupter):

https://en.wikipedia.org/wiki/Residual-current_device

These are usually built into the electrical outlet (or one outlet may provide the GFCI/RCD for several connected outlets). A whole-house RCD as described above would be a wonderful thing.

From personal experience, a GFI-ied house can also be a nightmare. A house can have a lot of outlets. Some of them well-hidden, unused, and long forgotten.

If the “test” button is ever unintentionally pressed, maybe from some furniture or whatever pressing against it, then your whole circuit goes down. But the breaker box shows no fault, and now you get to waste the afternoon inspecting every inch of wall space for an upset outlet.

This is a problem you don’t have when the GFCIs are in the breaker box, though.

Yea. I have three of them for my condo. One for the "wet-rooms" (bath and such), one for the electrical stove in the kitchen, and one for the rest. Though it wasn't so initially. Got upgraded about 10 years ago. Now the breaker box says 400v 63A and I wonder how I ever reasonably could use that here.

You have a condo, so the 400v is because the building is being supplied with three-phase power - 63A gives you a total of 25KW which is certainly a lot, but normal residential service is usually 240V @ 100A because of HVAC needs so it’s really more or less the same.

RCD breakers really are a wonderful thing though, I had my second small fridge knocked out because I had accidentally hit the test button of the outlet near the kitchen sink that the dining room outlet was fed from - having it at the breaker makes it a whole lot less confusing and removes the searching for the protected outlet conundrum.

Depending on where you are in the US GFCI breakers might be required these days in certain scenarios. Dual AFCI/GFCI breakers are certainly available at the hardware store. They're expensive though so it seems most people don't use them unless required to (which is crazy IMO).

Related but different, AFCI breakers are now required where I'm at in bedrooms and similar spaces where you wouldn't expect appliances to be plugged in.