This isn't technically home DIY but I think the answer should be the same. I have a power system with an incoming supply of 125A 3ph. This is split to several 16A sockets. Let's take 6 for example:
I have 6x 16A sockets the are downstream of individual RCBOs which themselves are downstream of a 125A MCCB. If I connect all the earths of the 16A sockets to an earth commoning block, which is in turn connected to the earth of the 125A, does the commoning block have to have a current rating of 125A? Surely not, and presumably we hope that a short circuit fault doesn't occur on all 6 sockets at the same time...?
I have 6x 16A sockets the are downstream of individual RCBOs which themselves are downstream of a 125A MCCB. If I connect all the earths of the 16A sockets to an earth commoning block, which is in turn connected to the earth of the 125A, does the commoning block have to have a current rating of 125A? Surely not, and presumably we hope that a short circuit fault doesn't occur on all 6 sockets at the same time...?