by ssl-3 | 2026-02-27 11:20:52+00:00
The only per-socket "circuit breakers" that I'm familiar with in the US are GFCI outlets. They're the ones that often have a glowy light inside of them, with Test and Reset buttons on the face.

These detect an imbalance of current flow betwixt the two current-carrying conductors and shut off when that imbalance exceeds a threshold, which does reduce the risk of shocks -- particularly in wet environments. The imbalance is evidence of a leak, possibly through a person -- so their intent is to halt that situation when it happens.

But our GFCI outlets have nothing at all to do with what is usually referred to, in the US, as a circuit breaker.

Regular circuit breakers are very different. They only detect overcurrent conditions and switch off -- much a fuse does, but with a reset function. They primarily protect the wiring of the home, and they do not give a fuck if you're being shocked. (Human factors and leakage current are not part of their purvey.)

GFCIs and fuses/circuit breakers are similar in that they both break circuits, but they're different in every other way.

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Meanwhile, in UK wiring, bathrooms do not have GFCI outlets. Instead, they have a shaver socket. That's a lower-voltage socket that also has a built-in transformer.

The transformer provides galvanic isolation. Galvanic isolation means the current imbalance that a GFCI is meant to detect and shut down can't happen in the first place, so it's safer in that way than a GFCI is.

With a shaver socket: Shaver in one wet hand, other wet hand touching metal water pipe? Perfectly safe: There's no opportunity for current to flow from one hand to the other. It's isolated.

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Meanwhile: Fuses. British electrical widgets generally use fused plugs. The fuse is to protect the wiring of the device being plugged in.

Why? Because homes are sometimes wired with what is called a ring circuit. This can increase ampacity while using less wire. A ring circuit with 2.5mm wire is typically be fused at 32 amps, which is way spicier than common 2.5mm wire can safely handle, much less a device being plugged in.

But it's OK, because it runs in a ring -- each outlet has 4 current-carrying wires, and they each feed eachother within that ring. The ring (all 4 wires of it) extends all the way to the box where the fuse/MCB [maybe with an RCD], or RCBO live. (In American terms, an MCB is like out central circuit breakers. The RCBO is a combination device that detects and protects against leakage current and overcurrent conditions, like the central GFCI breakers that some homes have for some circuits.)

Rings safe as long as both legs of the ring remain contiguous and are never fucked with improperly.

For the history: The UK does use ring circuits because they had a fuck of a bad time rebuilding after WWII, and they decided that this would save them money and let it gone quicker. They were probably right about this, for them at that time.

But that means their plugs need fuses. So it be.

We don't use ring circuits in the States, because we've never had a post-electrification war here and the opportunity to broadly start over has never forced itself.

We don't usually use fused plugs, either -- our unfused pluggy-inny things are supposed to be able to trip our common 15 or 20a breakers without much drama. (Except when their design doesn't allow that. In those cases, they're supposed to have their own protection devices -- which is why Christmas lights have fused plugs in the US. Their tiny little wires can't carry enough current to trip the branch circuit's breaker in the event of a dead short. We got to choose between using bigger wires for the lights themselves, or fusing the plugs, or having houses burn down. We chose fuses. We were probably right about this, for us.)

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Two different countries, two different pathways. Both paths work well-enough, but they're not the same.

And it's fine. :)