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pc1966

Arms
Esteemed
What is interesting there is they are higher then BS 18th and the method generally used here.

For example, a 32A B-curve MCB here has the "instantaneous" magnetic trip at 3-5 * In so 96-160A and we would assume the worst-case, so to hit the sub-0.4s time you need Zs to be below 230V / 160A = 1.44 ohms. This is already below your 1.8 by a noticeable amount!

Next we assume you have to meet this at lower limit of UK supply voltage specification (95% of 230V) and when the cables are hot (so if measured cold, 80% of worst-case resistance) leading to a verification value on cold testing of:

1.44 * 0.95 * 0.8 = 1.09 ohm (given in the IET's On-Site Guide Table B6 as 1.1 ohm)

So Aus/Nz are 64% more optimistic!
 

telectrix

-
Mentor
Arms
Esteemed
australians are more sensible. when do we run cables @ 70deg.c? and when is our voltage down to 216V? load of crap. just anothe reason for IET to bring out a new edition to increase their pension funds at our expense.
 
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