How much load for 50mm2 cable?

There's no such Word as "'Ampacity". The current carrying capacity of 50mm cable is around 300A continuous or 365amps @ 60% duty cycle. It's generally used for engine starter circuits or high current welders.

'Ampacity' is a North American term for the 'current-carrying capacity' of a cable. It is not used in most other English-speaking countries.