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Ever thought about ... ?

gkenyon
I was asked a series of interesting questions this week about fault protection and overload protection for a particular application. Some of these really make you think, and the physics doesn't always lead you where you think you'd go.


Dropping out of all this, was me pointing out something interesting which I wonder whether it's ever crossed the minds of contributors to this Forum ... so here goes.


Ever thought about what, in typical UK installations, protects the electronics in a plug-in [to a standard BS 1363-2 socket-outlet] phone charger / wall-wart type power converter against:

(a) Fault current (consider both cases of L-N and L-PE); and

(b) Overload current ?




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    The ratings available from Bussmann are 1, 2, 3, 5, 7, 10 and 13 amps and IR = 6 kA, as the fuse wire is enclosed, which is probably more relevant than anything else.

    https://www.electricalworld.com/Images/ModelDescriptions/Bussmann Consumer Fuse Specification Data Sheet Technical Information Electricalworld.pdf


    A Polish electrician asked me “What is it with the English electricians and switched fused connection units” I laughed and said good question.


    All these FCU are installed then the fuse doesn’t provide as close as protection as it could do, often being rated three times higher than it needs to be. But our European neighbours are quite happy protecting the same appliances with a 16-amp circuit breaker, often a C type just to compound things.


    This is wandering off from Graham’s specific question about USB chargers, but maybe the answer is it doesn’t matter if they fail without blowing a fuse or tripping a MCB, so long as they fail safe.
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  • 0
    The ratings available from Bussmann are 1, 2, 3, 5, 7, 10 and 13 amps and IR = 6 kA, as the fuse wire is enclosed, which is probably more relevant than anything else.

    https://www.electricalworld.com/Images/ModelDescriptions/Bussmann Consumer Fuse Specification Data Sheet Technical Information Electricalworld.pdf


    A Polish electrician asked me “What is it with the English electricians and switched fused connection units” I laughed and said good question.


    All these FCU are installed then the fuse doesn’t provide as close as protection as it could do, often being rated three times higher than it needs to be. But our European neighbours are quite happy protecting the same appliances with a 16-amp circuit breaker, often a C type just to compound things.


    This is wandering off from Graham’s specific question about USB chargers, but maybe the answer is it doesn’t matter if they fail without blowing a fuse or tripping a MCB, so long as they fail safe.
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