"Ed Sirett" wrote in message
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In real life PSC of 6kA are uncommon although theoretically possible.
A plausible scenario would be a cleaners' socket in a meter cupboard on
the ground floor of a block of flats containing the sub-station in the
basement.

I quite agree, but the socket is an irrelevance really - I'm talking about
any S/C fault which occurs close to the start of a final circuit, and
therefore doesn't benefit from the reduction in fault level which the final
circuit gives.

I thought the resistance of the MCB might come to our rescue but I've just
measured one and it's DC resistance is less than 0.01 ohms as measured by
good test gear. Likewise the meter might help out a bit? However the AC
impedance might be quite a bit more as MCBs do get a little warm in
operation.

Pure reactance ("AC impedance") wouldn't create any heat.

On such short circuits what fault could you have that both gave
rise to a full short circuit and which did not implicate the cable.

Well, I'm really talking about cable faults in this case (e.g. someone bangs
something large and metallic right through the cable).

What I'm fishing for is the relevance/application of the adiabatic
calculations in such situations.

Will