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Logic problem in OSG - trivial

Ziggie
Page 79 OSG (blue edition)


Lcn is max fault current .......although the breaker may no longer be usable.

Lcs is max fault current .......can interupt safely without loss of performance.


.........


For domestic installations, the PFC is unlikely to exceed 6kA , up to which value the Lcn will equal Lcs.


usable , maybe usable, certainly usable?


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  • 0
    If you go above Icn, the breaker may not stay in one piece.


    If you remain below Ics, the breaker should remain serviceable - i.e. you fix the short circuit and reset.


    If the short circuit current is between Ics and Icn, the breaker should remain in one piece, but the innards cannot be guaranteed to work again, so it must be replaced.


    For BS 60898 breakers rated at <= 6 kA, Ics = Icn; and for > 6 kA and <= 10 kA, Ics = 0.75 x Icn.


    Fairly obviously, the Ics should be less than the PSCC, which is almost always the case for domestic supplies.
Reply
  • 0
    If you go above Icn, the breaker may not stay in one piece.


    If you remain below Ics, the breaker should remain serviceable - i.e. you fix the short circuit and reset.


    If the short circuit current is between Ics and Icn, the breaker should remain in one piece, but the innards cannot be guaranteed to work again, so it must be replaced.


    For BS 60898 breakers rated at <= 6 kA, Ics = Icn; and for > 6 kA and <= 10 kA, Ics = 0.75 x Icn.


    Fairly obviously, the Ics should be less than the PSCC, which is almost always the case for domestic supplies.
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