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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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  • 0
    A C16  breaker is normally assumed as the worst case for things being supplied by a Schucko socket. In reality the B32 is not a million miles off.

    For vaporising PCB links, the 6kA or whatever you think that is the peak current is not as serious in terms of damage as how long it flows for - and the power supply designs with the fusible resistors in series do not have that problem anyway, as a dead short in the electronics "just" puts full mains across the few ohms - so for the time it takes to go 'phut' the current is in the high tens of amps up to perhaps a couple of hundred or so.


      examples     "The resistor will fuse safely if 120 or 240 V is applied. The time to fuse depends on the resistance value"
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  • 0
    A C16  breaker is normally assumed as the worst case for things being supplied by a Schucko socket. In reality the B32 is not a million miles off.

    For vaporising PCB links, the 6kA or whatever you think that is the peak current is not as serious in terms of damage as how long it flows for - and the power supply designs with the fusible resistors in series do not have that problem anyway, as a dead short in the electronics "just" puts full mains across the few ohms - so for the time it takes to go 'phut' the current is in the high tens of amps up to perhaps a couple of hundred or so.


      examples     "The resistor will fuse safely if 120 or 240 V is applied. The time to fuse depends on the resistance value"
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