The same bimetallic break was used in old circuit breakers. You would literally have to wait for the metal to cool down before the connection could be restored. Not sure if it's still used or we use something fancier these days?
The bimetallic strip is for overcurrent protection over a period of time. For example, if you are running an appliance using a constant 15A on a 10A breaker. The breaker will pop, but not instantly, and I guess you may have to wait a bit for the metal to cool down, though it never happened to me.
But there is also a short-circuit protection, it uses a solenoid to quickly trip the breaker when the current is way over its rating. The fancier types (with GFCI) also pop if the return current is not the same as the input current, this is to prevent electrocution.
The problem with drawing too much current is that things can overheat, and it is more of a problem during heat waves as well.
[1] https://www.tekdok.dk/files/CA908024E_Trip_curve_2021.pdf
I haven't given it a lot of research because NEC requires 125% (1/.8) for continuous loads (for conductor protection).
Perhaps my experience was hot ambient/panel.
> Modern circuit breakers are much fancier. They break... when the currents passing in both directions [is] unequal
You can get devices which fit into a standard circuit breaker slot which perform both functions. However a conventional circuit breaker (which are still widely available) doesn't do any of that.
[0] Ground Fault Circuit Interruptor
[1] Residual Current Device
in the UK such a device is called an "RCBO" aka "Residual Current Breaker with Over-Current (protection)"
good summary here from schneider
https://eshop.se.com/in/blog/post/what-is-the-difference-bet...
But, what is quite common in the last 30 years are AFCIs, arc fault interruptors which are code for pretty much all living area branch circuits (just not bathrooms). These are built in to the circuit breaker. You can get dual GFCI/AFCI breakers, but these tend to be expensive and not commonly used. Nobody wants to have go down to the basement just because of a ground fault in the kitchen. Also the propensity for GFCIs to nuisance trip increases with the length of the branch circuit. There’s also cases where they are specifically disallowed.
Part of the issue with "not terribly common" is that no one ever retrofits these things into older houses and new houses only get them where code requires it since it's an increased cost.
They should of course be added to any kitchens or bathrooms. It's cheap insurance.
You mean neutral or return wire. No current should be normally passing through the ground wire. In fact in the US at least, GFCIs can be used on grandfathered ungrounded outlets. When you buy GFCI outlets they come with little stickers: “No Equipment Ground” to affix on the outlet in that case.