Today I’ve further refined the wiring of the relays on the HEMS. At the time that I’d originally wired it I didn’t have small enough flex, or indeed multi core, which created an unnecessary number of cables (one per used relay) of over large size (and thus difficult to insert into the terminals). During the week I acquired some smaller gauge multi core allowing me to wire all three relays with a single cable containing one live feed and three switched live returns.

Of the 5 incoming / outgoing cables at the bottom (left to right):

1. Incoming mains (live / neutral / earth) from mains plug
2. Live and switched live to / from ImmerSUN output relay to activate car charger.
3. Live and switched lives to / from HEMS to activate car charger and water heating.
   • Red – live to contacts
   • Green – switched live for car charger direct – charge in response to price
   • Black – switched live for car charger indirect via ImmerSUN relay output – enable proportional charge in response to surplus PV
   • White – switched live for water heating – heat in response to price
4. Outgoing mains (switched live / neutral / earth) to RF solutions radio transmitter to activate car charger, and on the second cable clamp..
5. Outgoing switched live and neutral to ImmerSUN Boost relay input to enable immersion heater.

The revised wiring diagram looks like this..

All of this still leaves one unused relay on the HEMS (HAT #3) and one unused proportional output on the ImmerSUN (#2; available for future expansion.

Initially even my smallest boot lace ferrules would not fit into the terminals on the HAT. Fortunately, once the ferrules has been crimped around the new cables, and flattened by squeezing in pliers, then the ferrules could be persuaded into the terminals.