The main Difference CSH30-120-200 is in the diameter of residual current sensor
CSH30 -> 30mm
CSH120 -> 120mm
CSH200 -> 200mm
I will try to give you more explanation in the below question
In Sepam M20 with sft2841 software, you can choose from the software if you will use CSH 120 as 2A rated or 20A rated
But Why in the software did not give you the option to choose between CSH 120 or CSH 200
The option to choose between 2A and 20A rated CSH depends on the residual current value you need to monitor. For example: in the Earth Fault protection if you choose 2A rating, you can set the threshold current between 0.2A to 30A, if you choose 20A rating, you can set the threshold current between 2A to 300A.
As for why there is no option to choose CSH120 or CSH200 in the SFT2841 software, because in term of measuring characteristics these 2 CSH models are almost the same. That is why SFT2841 consider them as the same CSH. Their differences are more on physical, which are their diameters and weights. CSH120 is 120mm in diameter and weigh at 0.6kg, while CSH200 is 200mm in diameter and weigh at 1.4kg.