just for interest (perhaps) OCP for RCCBs

Humm it sounds like a bit of smoke and mirrors on this one. Applying normal BS 7671 rules for overload protection would mean that you wouldn't normally rely on assumption of diversity to provide overload protection, but would need a suitably rated protective devices (either upstream or downstream).

That didn't happen with RCCBs inside CUs not because of any gap in BS 7671 as such, but because the internals of equipment subject to other standards (such as BS EN 61439 for CUs) is covered by those standards and not BS 7671. So BS 7671 would apply if you were putting an an RCCB in its own box, but what happens inside a CU marked ‘max load 100A’ is down to BS EN 61439 alone. I might suspect there's been an underlying change in BS EN 61439 which has driven all this.

I wonder if the corresponding BS 7671 change (no doubt copied down from IEC/CENELEC) is due to the tradition in other countries of treating a CU/DB as just an enclosure into which the electrician is expected to assemble on-site whatever component parts they think best for that particular installation, from whatever mix of manufacturers they prefer. It's almost as if the UK manufacturers insistence on treating an entire CU as a ‘type tested assembly’ which can only be configured according to the manufacturer's instructions has come back to bite them.

   - Andy.

Humm it sounds like a bit of smoke and mirrors on this one. Applying normal BS 7671 rules for overload protection would mean that you wouldn't normally rely on assumption of diversity to provide overload protection, but would need a suitably rated protective devices (either upstream or downstream).

That didn't happen with RCCBs inside CUs not because of any gap in BS 7671 as such, but because the internals of equipment subject to other standards (such as BS EN 61439 for CUs) is covered by those standards and not BS 7671. So BS 7671 would apply if you were putting an an RCCB in its own box, but what happens inside a CU marked ‘max load 100A’ is down to BS EN 61439 alone. I might suspect there's been an underlying change in BS EN 61439 which has driven all this.

I wonder if the corresponding BS 7671 change (no doubt copied down from IEC/CENELEC) is due to the tradition in other countries of treating a CU/DB as just an enclosure into which the electrician is expected to assemble on-site whatever component parts they think best for that particular installation, from whatever mix of manufacturers they prefer. It's almost as if the UK manufacturers insistence on treating an entire CU as a ‘type tested assembly’ which can only be configured according to the manufacturer's instructions has come back to bite them.

   - Andy.