electricalforum.nz

Existing 16mm Mains supplying single phase 3-4 bed house. 63A Mains switch, assumption of a 63A pole fuse.
Additional meter being installed in the msb for consumer. The house supply/mains needs to go through this meter however 16mm is to big for the terminals of the meter. The supplier of the meter has said that the 16mm can be reduced down to 10mm in a terminal block/connector to go through the meter to supply the whole house, its fine because its "short".
How would the cable being "short" change the inherent current rating of the 10mm cable? and how long is short to achieve this purpose?

Wiring in a switchboard is rated as unenclosed in air. So you would use the rating from 3008 table 4.
The rating of 10mm² is 79A in table 4 column 2 - (or 76A if you follow the guidance in table 3(1) and use the table 4 column 5 rating).
So it's not really accurate to say that it's just because it's "short".
You can probably get a reducing crimp link for 16-10mm².

The point of "short" in such cases is not related to CCC, but to volt drop.
If the entire run were 10 mm2, there would be considerably more volt drop than for 16 mm2. But reduced 'tails' at the end have only a very small contribution to volt drop; not even worth calculating for length < 1m.

Your assumption of 63A overcurrent protection for the mains is likely correct, but since you are installing new cable you need to confirm this - networks are required to provide s/c & fault protection (for mains), but overload protection is installers' responsibility.

Also, depending on exact circuit as-built, this work may be "mains work" that requires inspection. But provided the new meter is downstream of main switch, that won't be an issue.