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Energy let-through for Type 2 MCB's ?

justinneedham

I'm nursing an elderly installation containing MK brand Type 2 breakers.

Does anyone have let-through energy curves for MK Type 2 32A MCB ? - Specifically LN5932.

Without any better data I'm likely to expect it to have I^2t no higher then a type C BS60898, and (based on 7x multiplier for instantaneous trip..), perhaps somewhere between a B and  C? Is that a safe assumption? 

I have curves for Wylex BS60898 and for one or two other brands. 

It's a bit of hand-waving I'd sooner not do if there are measured curves somewhere out there?

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  • 0

    I think that the point that Zoomup is making is how often in a domestic installation would you be selecting the conductor size of the CPC? How often would you be wiring in singles?

    The adiabatic isn't just for singles - most T&E cables have reduced c.p.c.s - 1.5mm² (or even 1.0mm² if it's an older 2.5mm²) on a 32A device isn't an automatic pass if the fault currents could be high.

       - Andy.

  • 0 in reply to AJJewsbury

    In the past with 2.5mm2 T&E cables with a 1.0mm2 C.P.C. protected by a 30 Amp bit of fuse wire for a ring, did we really have lots of melted cables or fires caused by that arrangement?

    Quote: 

    "OK do the calculation for a 2kA or 1.5kA  fault current then if you prefer - it's still likely to be more than would reasonably be expected."

    If so the breakers and cables will be happy with a lower fault current. Or a large one, but not for long eh?

    Z.

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  • 0 in reply to AJJewsbury

    In the past with 2.5mm2 T&E cables with a 1.0mm2 C.P.C. protected by a 30 Amp bit of fuse wire for a ring, did we really have lots of melted cables or fires caused by that arrangement?

    Quote: 

    "OK do the calculation for a 2kA or 1.5kA  fault current then if you prefer - it's still likely to be more than would reasonably be expected."

    If so the breakers and cables will be happy with a lower fault current. Or a large one, but not for long eh?

    Z.

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