There's no prohibition on mixing parts from different manufacturers in a single bit of switchgear. However, you then take on the responsibility of ensuring that the whole enclosure complies with BS EN 61439 including (I'm guessing here, not having the millionaire income necessary for easy access to such standards) the ability to not arc on 6 kV spikes, on the enclosure's ability to contain hot gases from CB's breaking of short circuits, that devices adjacent to each other at max load don't overheat, etc.
There's no prohibition on mixing parts from different manufacturers in a single bit of switchgear. However, you then take on the responsibility of ensuring that the whole enclosure complies with BS EN 61439 including (I'm guessing here, not having the millionaire income necessary for easy access to such standards) the ability to not arc on 6 kV spikes, on the enclosure's ability to contain hot gases from CB's breaking of short circuits, that devices adjacent to each other at max load don't overheat, etc.
