type of breaker

[i=p/u]

in a hotel i want to change an old brown mcb from 50A too 20A or 30A any of you know the bs number im after, i know long shot but it has the rating engraved on the top of the switch in white...

 

[i=p/u]

well they get it tested every year i think. i have asked for the past test results yesterday.... so might get them over weekend and have a nosey