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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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    AJJewsbury:

    Thanks Graham - that looks similar to my earlier attempt. I'll give it some thought...


    Superficially though it doesn't look too bad against the figures I've got for MCBs - at 3kA

    B16 15,000A²s

    C16 18,000A²s

    C20 22,000A²s

    B32 18,000A²s

    (which also suggest a 1.0mm² conductor (with a k²S² of 13,225) isn't protected)


    I understand that our continental cousins typically prefer C types for their socket circuits - so if anything our B32 look like a better choice.

        - Andy.

     


    Those figures look like they're from the standard ... but the Type C ones are too high at 3 kA


    The figures for let-through at 3 kA fault current, from the current standard are:



    • Type B  ≤16 A - 15,000 A²s

    • Type C  ≤16 A - 17,000 A²s

    • Type B > 16 A ≤ 32 A - 18,000 A²s

    • Type C > 16 A ≤ 32 A - 20,000 A²s



    In reality, mcb's will have let-through much lower than BS EN 60898 / BS EN 61009.


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  • 0
    AJJewsbury:

    Thanks Graham - that looks similar to my earlier attempt. I'll give it some thought...


    Superficially though it doesn't look too bad against the figures I've got for MCBs - at 3kA

    B16 15,000A²s

    C16 18,000A²s

    C20 22,000A²s

    B32 18,000A²s

    (which also suggest a 1.0mm² conductor (with a k²S² of 13,225) isn't protected)


    I understand that our continental cousins typically prefer C types for their socket circuits - so if anything our B32 look like a better choice.

        - Andy.

     


    Those figures look like they're from the standard ... but the Type C ones are too high at 3 kA


    The figures for let-through at 3 kA fault current, from the current standard are:



    • Type B  ≤16 A - 15,000 A²s

    • Type C  ≤16 A - 17,000 A²s

    • Type B > 16 A ≤ 32 A - 18,000 A²s

    • Type C > 16 A ≤ 32 A - 20,000 A²s



    In reality, mcb's will have let-through much lower than BS EN 60898 / BS EN 61009.


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