Not uncommon, 63Amp devices are specified to be fed by cables larger than 35mm sq.
While reviewing the consultant’s design, as represented by the schematic drawing, compare the cable sizes to the device sizes. Not uncommonly, 63Amp isolators or ATS are indicated to be fed by cables larger than 35mm sq.
Risk
In such a case, the cable will be too large to fit within the terminals. Consequently, you should question the cable size or ATS size.
Solution
If the cable is oversized because of its length aiming to reduce earth fault impedance then spreader box with custom terminals will be required.