I was really surprised when I opened this up. I thought it was going to be much more complex.

These devices are purely intended to break current limited faults like overloads, and not really ideal for breaking high short-circuit currents.

One example of their use is in a motor circuit where the current increases dramatically when the motor stalls, and it's important to switch it off quickly before the motor suffers thermal damage.

They can also find use on the secondary side of transformers, where the fault current is inherently limited to a manageable level.

Here's a link to "Let's be techs" HVAC maintenance channel:-
https://www.youtube.com/@UChH1LTsB4IzJ_qiTh23_pJQ

If you want one of these for a non-critical application or just to open, then here's a link to the item on AliExpress (not a sponsor).
This is an affiliate link, but that will not affect the price you pay.
https://s.click.aliexpress.com/e/_c3f7Pbdj
The cost is low - maybe too low, so treat these as a novelty item, and if you have a safety critical situation then buy one from a trusted source. Even from a prominent supplier they are not very expensive.



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