electricalforum.nz

"Discrimination on overload and instantaneous operation may be
deemed to be provided when C1 ≥ 2 × C2, e.g. C1 curve 63 A
with C2 curve 32 A (see Figures 2.11 and 2.12.)"

This says a 63A with a 32A but using the method of calculation 2*32=64 so a 63A MCB is not ≥ a 32A MCB

"(A) the overload setting of C1 ≥1.6 × C2, e.g. 1000 A with 630
A; and
(B) the instantaneous setting of C1 ≥1.6 × C2, e.g. C1=5 ×
1000 A with C2=5 × 630 A."

630*1.6=1008
630*5*16=5040

1000*5=5000

Same here for the 250 to 799 requirements

Am I missing something or screwing something up or is this some sort of mistake? I highly doubt it's a mistake when it happens in 2 cases

I see both these have been changed to actually work properly in the 2018 version

They key to this apparent anomaly is the wording "deemed to be provided".
That means it doesn't matter whether the actual long-form calculation works, all that matters is the short-form "x2" calculation

I don't understand what you mean sorry Alec

The short form x2? But the resulting 63A is less the 32A x2

The long form would be a detailed calculation based on the operating curve data for the particular devices. The short form lets us get on the the job using a 'deemed to comply"; regardless of whether it actually complies.
The fact that the example doesn't quite match (by 1 A or 3.1%) doesn't invalidate the deemed-to-comply method, it's just not a very good example. However i believe it was deliberately chosen to indicate that such a small variance doesn't actually matter, when we're already in a 'deemed-to-comply" situation.
That's because all such are designed to be on the safe side.

The change between current and latest editions if from x2 to x 1.5; which is a change rather than a clarification or correction, and cuts us even more slack.

Ah, ok right, I see what you mean, thank you!