On 08/11/2017 22:24, Tim Watts wrote:

3) If you overload a cable to say twice its rating and the MCB takes say
Â*15-20 minutes to trip, the cable has not instantlo y heated up to
beyond 70C - it's gradually overheating and the Type B curve is designed
to reflect that.

It's nothing to do with the B curve:-)

The same applies to C and D MCBs


--
Adam