Hi There
32A "B" curve, tripping current to trip the thing in the required time is 5 times its rated current so 5 x 32 = 160.
You got 230v so V/I = R [as Andy said] gives a Zs of 230 / 160 = 1.43 ohms. Bearing in mind that when you measure it with your meter you will need to be below 0.8 of that, so 1.14 ohms
You are obviously not going to be able to achieve this, so it is back to the RCD to provide ADS.
You could use the type "S" 100mA one to protect the supply cable as it is a distribution circuit, BUT from then on you will need "ordinary" ones to achieve the disconnection times for the final circuits to the sockets that feed the caravans or whatever, as a type "S" one will be too slow..
I am certainly not an expert at this, so check with the others if this sounds ok!!!!!
john..