On 30/08/2019 19:49, ARW wrote:
On 30/08/2019 19:08, wrote:
I have a couple of external sockets that are fed from an RCBO which
also provides power (via about 30m of buried 3-core SWA cable) to a
class II Well pump and controller. The SWA armour and earth conductor
are connected to the house earth solely by the CPC in the T&E cable.
I'm wondering about putting a small weather-proof CU at the Well so I
can use its supply for a remote socket, garden lights, and maybe a
gate controller. The question is whether to TT the remote CU (but the
SWA will still have to be fed from the RCBO) or whether to add a 10mm
earth cable between the MET and the SWA armour so I can use the
exported earth. The house has a dedicated TN-C-S supply from a 2-wire
overhead feed, but I have fitted an additional ground rod so
(hopefully) the loss of the supply neutral should not cause a safety
issue.

What would the experts do?

You cannot make a TT supply from a 30mA RCBO.


I can see a possible issue with discrimination, but if the RCBO (or RCD)
is just measuring L-N current imbalance then why would there be a
functional problem?