So, we are assuming that there is a spare 45A cpd in the board but that there is no cable connected at present.?? That certainly has not been confirmed by the OP.
If a new cable is required then 10mm would be required as 6mm isn't up to 45A except in completely ideal conditions (ref method C).
If 45A is OK will depend on the makers instructions for the appliance, of course.
I am trying to get some more information from the OP.
By saying that I am hoping he might says something like
"oh no, there is a 45A fuse laying around in the cupboard but there is no extra space for it in the board"
By the way, CPD is an abbreviation for circuit protective device. A fuse is one type of CPD. I am surprised that you don't know that.
You have been in the jungle too long. Do you see those two squiggly things after the word present?. Those are question marks. I am querying if there is a cable already connected. Otherwise I would have made it a statement and there would not have been any squigglys at the end of the sentence.
Go play with your monkey - you are not adding any value.
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