Cartridge Fuses in Domestic Fuse Boxes.

I'd imagine cost. Both of the test gear to successfully test a circuit breaker at up to its breaking capacity, and more importantly, the cost of the breaker itself.   And this leads back to your point. Should the breaker not be designed to survive a possibly unlimited number of dead shorts at its rated capacity, or should the test be reserved for installation and at every EICR... with a decrementing counter on the breaker body itself somewhere? More expense. Breakers are a couple of pounds each, new, name brand, plus VAT. Designing in the ability to survive a fault AND continue operating would at least quadruple that.


All that's currently required is that a decent sample of the batch fails SAFELY in the event of a catastrophic fault.  If the internals of the breaker are trash... provided it didn't destroy the rest of the DB, and opened the circuit, it passes.


I actually like cartridge fuses for just this reason. Their MO is to destroy themselves, so they automatically get replaced. And are well proven.


But I'd posit that given the number in service, and the number of major problems caused by their failure... that MCB's have actually managed to pass that bar also?


Remember, functional testing of 'things that live in the CU' is only a thing because of RCD's, which can, by their nature, be tested under severe 'fault' conditions without actually endangering anything.


Sorry for the ramble :)

I'd imagine cost. Both of the test gear to successfully test a circuit breaker at up to its breaking capacity, and more importantly, the cost of the breaker itself.   And this leads back to your point. Should the breaker not be designed to survive a possibly unlimited number of dead shorts at its rated capacity, or should the test be reserved for installation and at every EICR... with a decrementing counter on the breaker body itself somewhere? More expense. Breakers are a couple of pounds each, new, name brand, plus VAT. Designing in the ability to survive a fault AND continue operating would at least quadruple that.


All that's currently required is that a decent sample of the batch fails SAFELY in the event of a catastrophic fault.  If the internals of the breaker are trash... provided it didn't destroy the rest of the DB, and opened the circuit, it passes.


I actually like cartridge fuses for just this reason. Their MO is to destroy themselves, so they automatically get replaced. And are well proven.


But I'd posit that given the number in service, and the number of major problems caused by their failure... that MCB's have actually managed to pass that bar also?


Remember, functional testing of 'things that live in the CU' is only a thing because of RCD's, which can, by their nature, be tested under severe 'fault' conditions without actually endangering anything.


Sorry for the ramble :)