The question of RCBOs and total leakage is interesting.

For a long time we (the folk I work with) have designed to a 1mA per amp upper limit, not for domestic installations but for equipment, so a 10 amp load needing EMC filters, may leak up to 10mA etc.
This is a consequence of the size of capacitors needed for a given degree of filtering and their impedance at 50Hz (for lower current loads the inductors can be larger and the capacitors smaller)..  It is not an accurate rule of thumb, and it is possible to do better, a lot better where 3 phases are involved, as things cancel, on the other hand a tendency to round up on the  filtering can sometimes lead to more leakage than a low current application really requires.  Note that much of what I do has to exceed the minimum CE marking requirements, which can be met with perhaps 3mA of leakage on a 13A load.

But ignoring that it fits more or less if 30A (or 32A? circuits  get  30mA RCD, and a 100A supply gets a 100mA one.

But a board with lots of 30mA RCBOs and a switch could leak N times just under 30mA and be running normally, making the installation CPC and bonding a dangerous thing to play with while operational, and to impose a limit on TT electrode performance that may not be appreciated at first glance.

I for one have 10 breakers in the CU at home, not because I have hundreds of amps of load, but because I like subdivision for convenience. Now that does not mean that I should expect or tolerate 300mA of leakage in normal operation ,but it does mean that checking electrode resistances becomes more important  (round here, ice age gravel means that a single rod is perhaps 100- 200 ohms when new)

In systems with a lot of RCBOs there would be a lot to be said for a 100mA slow trip device further back.

Mike.

The question of RCBOs and total leakage is interesting.

For a long time we (the folk I work with) have designed to a 1mA per amp upper limit, not for domestic installations but for equipment, so a 10 amp load needing EMC filters, may leak up to 10mA etc.
This is a consequence of the size of capacitors needed for a given degree of filtering and their impedance at 50Hz (for lower current loads the inductors can be larger and the capacitors smaller)..  It is not an accurate rule of thumb, and it is possible to do better, a lot better where 3 phases are involved, as things cancel, on the other hand a tendency to round up on the  filtering can sometimes lead to more leakage than a low current application really requires.  Note that much of what I do has to exceed the minimum CE marking requirements, which can be met with perhaps 3mA of leakage on a 13A load.

But ignoring that it fits more or less if 30A (or 32A? circuits  get  30mA RCD, and a 100A supply gets a 100mA one.

But a board with lots of 30mA RCBOs and a switch could leak N times just under 30mA and be running normally, making the installation CPC and bonding a dangerous thing to play with while operational, and to impose a limit on TT electrode performance that may not be appreciated at first glance.

I for one have 10 breakers in the CU at home, not because I have hundreds of amps of load, but because I like subdivision for convenience. Now that does not mean that I should expect or tolerate 300mA of leakage in normal operation ,but it does mean that checking electrode resistances becomes more important  (round here, ice age gravel means that a single rod is perhaps 100- 200 ohms when new)

In systems with a lot of RCBOs there would be a lot to be said for a 100mA slow trip device further back.

Mike.