Faulty British General circuit breaker autopsy.

This faulty breaker was sent by Thomas Nagy, who has a very interesting YouTube channel documenting his daily working life as an electrician in London.
https://www.youtube.com/channel/UC6EJTy6p58ZW16PEljSn4Qw

The failure mode is interesting and highlights the fact that a breaker could fail in a manner where the magnetic tripping mechanism might not work. (This one failed safe.)
It's worth mentioning that many of these breakers have similar internal construction, so this issue could affect any brand.

When you test an RCD/GFI by pressing the test button a full functional test is performed internally. It's not just a simple latch release.
There's no easy equivalent test you can apply to a traditional MCB (miniature circuit breaker) to test if it is functioning within spec on site.

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