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Please bear/bare with me as I try to explain.

Rather than connecting to an existing ring main I'd prefer to put in a separate ring main for our element heated thermal store. Unfortunately The domestic Consumer unit has no spare ports for this, but the adjacent consumer unit, put in for the solar system, has.
Is there any reason why this spare port could not be brought into service for a domestic application?
I would very much welcome thoughts from anyone with greater knowledge or experience in such a case.

You’d want to put in a radial rather than ring. But sure you can use the additional CU so long as the breaker you fit is type approved for that enclosure.

How powerful is the heating element?

(This work is notifiable.)

How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

We have 3 immersions (3kW each) each of which had its own Radial from the main CU when first setup. When we added an Eddi 2 of the immersion were connect to that using one of the previous radials - so we can only have 3kW supply to the TS from either of 2 immersions. The redundant port in teh Cu was repurposed for something else.

Countrypaul wrote: ↑Sat Sep 25, 2021 12:47 pm How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

We have 3 immersions (3kW each) each of which had its own Radial from the main CU when first setup. When we added an Eddi 2 of the immersion were connect to that using one of the previous radials - so we can only have 3kW supply to the TS from either of 2 immersions. The redundant port in teh Cu was repurposed for something else.

3 immersions each with its own radial is a bit extravagant! I'd have run a single 40A or 45A circuit in 6mm with each immersion having its own 13A FCU next to the cylinder. Some people might have run a single 32A circuit in 4mm and claimed "diversity" (it would be unlikely for all 3 immersions to be on at the same time) but that is unnecessary economic restraint IMO.

How powerful is the heating element?

Thanks for prompt and positive reply Stinsy. 3 kW, two off. Thermal store is 210 litre. Thanks too for mentioning radial. I'm running two 2.5mm2 cables into a double socket so I guess ring main was an elaborate description.

How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

Thanks Countrypaul, No diverter, although it is tempting. But with a 40 kWh, battery on wheels in the drive, I'm hoping one day to link it up via V2H/G which might then make the diverter somewhat superfluous! We've an almost 9 kW array on the roof and in fine weather generating 6 kW. Ample to power just the one element which is all we do. But there has been the odd occasion when a shorter heating period would have been convenient. Hence for putting them on their own circuit so not overloading existing supply.

Thanks too for the tip re Notifiable.

Stinsy wrote: ↑Sat Sep 25, 2021 2:04 pm

Countrypaul wrote: ↑Sat Sep 25, 2021 12:47 pm How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

We have 3 immersions (3kW each) each of which had its own Radial from the main CU when first setup. When we added an Eddi 2 of the immersion were connect to that using one of the previous radials - so we can only have 3kW supply to the TS from either of 2 immersions. The redundant port in teh Cu was repurposed for something else.

3 immersions each with its own radial is a bit extravagant! I'd have run a single 40A circuit in 6mm with each immersion having its own 13A FCU next to the cylinder. Some people might have run a single 32A circuit in 4mm and claimed "diversity" (it would be unlikely for all 3 immersions to be on at the same time) but that is unnecessary economic restraint IMO.

Running a sinlge radial was considered by the electricians, but we knew the PV diverter would be in the ground floor utility room (1m from the CU) so that meant all 3 immersions had to be wired separately back to the utility anyway so they thought might as well put them on separate MCBs. It was a as much a case of future proofing as it was convienient. We also knew at some periods all 3 immersions would be on at the same time, using E7 before we got an ASHP. One of the reaons I asked about no of immersions and likelyhood of a diverter.

Adokforme wrote: ↑Sat Sep 25, 2021 2:23 pm

How powerful is the heating element?

Thanks for prompt and positive reply Stinsy. 3 kW, two off. Thermal store is 210 litre. Thanks too for mentioning radial. I'm running two 2.5mm2 cables into a double socket so I guess ring main was an elaborate description.

How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

Thanks Countrypaul, No diverter, although it is tempting. But with a 40 kWh, battery on wheels in the drive, I'm hoping one day to link it up via V2H/G which might then make the diverter somewhat superfluous! We've an almost 9 kW array on the roof and in fine weather generating 6 kW. Ample to power just the one element which is all we do. But there has been the odd occasion when a shorter heating period would have been convenient. Hence for putting them on their own circuit so not overloading existing supply.

Thanks too for the tip re Notifiable.

I wouldn't use 13A sockets for immersion heaters unless you really need to. The plugs & sockets have a habit of getting hot and if left overheating, much better off wirng them in properly imho - but I'm not a sparks.

What will happen when the BEV is not present, or is fully charged, will you just accept exporting all the excess production? I know some systems (Eddi & Zappi is one of them) can allow you to setup priority for BEV vs immersion, limit the rate at which the BEV charges etc.

Countrypaul wrote: ↑Sat Sep 25, 2021 2:23 pm

Stinsy wrote: ↑Sat Sep 25, 2021 2:04 pm

Countrypaul wrote: ↑Sat Sep 25, 2021 12:47 pm How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

We have 3 immersions (3kW each) each of which had its own Radial from the main CU when first setup. When we added an Eddi 2 of the immersion were connect to that using one of the previous radials - so we can only have 3kW supply to the TS from either of 2 immersions. The redundant port in teh Cu was repurposed for something else.

3 immersions each with its own radial is a bit extravagant! I'd have run a single 40A circuit in 6mm with each immersion having its own 13A FCU next to the cylinder. Some people might have run a single 32A circuit in 4mm and claimed "diversity" (it would be unlikely for all 3 immersions to be on at the same time) but that is unnecessary economic restraint IMO.

Running a sinlge radial was considered by the electricians, but we knew the PV diverter would be in the ground floor utility room (1m from the CU) so that meant all 3 immersions had to be wired separately back to the utility anyway so they thought might as well put them on separate MCBs. It was a as much a case of future proofing as it was convienient. We also knew at some periods all 3 immersions would be on at the same time, using E7 before we got an ASHP. One of the reaons I asked about no of immersions and likelyhood of a diverter.

That makes more sense. Nothing wrong with putting the diverter next to the CU and wiring as you did kept that option. It is more normal to place the diverter next to the cylinder but it doesn't make much difference. And if the system is designed for all 3 immersions to be running simultaneously then you shouldn't apply diversity.

Adokforme wrote: ↑Sat Sep 25, 2021 2:23 pm

How powerful is the heating element?

Thanks for prompt and positive reply Stinsy. 3 kW, two off. Thermal store is 210 litre. Thanks too for mentioning radial. I'm running two 2.5mm2 cables into a double socket so I guess ring main was an elaborate description.

How many elements (immersion heater?) of what power will be used for the thermals store? Will you be using a PV diverter?

Thanks Countrypaul, No diverter, although it is tempting. But with a 40 kWh, battery on wheels in the drive, I'm hoping one day to link it up via V2H/G which might then make the diverter somewhat superfluous! We've an almost 9 kW array on the roof and in fine weather generating 6 kW. Ample to power just the one element which is all we do. But there has been the odd occasion when a shorter heating period would have been convenient. Hence for putting them on their own circuit so not overloading existing supply.

Thanks too for the tip re Notifiable.

Thanks for the additional information.
- A radial run in 2x lengths of 2.5 is non-conventional, that isn't to say it is prohibited but it could present challenges in future (eg if you needed an EICR for any reason).
- Most double sockets are only rated for 13A combined. Connecting 2x 13A loads would overload it. In any case connecting an immersion via a plug/socket isn't recommended. Use a FCU instead.
- For your situation here is what I would suggest: 1) If both immersions can be used simultaneously run a 32A radial in 4mm. 2) If only one immersion is likely to be used (EG you're using an E7 controller / solar diverter) then either a 16A radial in 1.5mm or 20A in 2.5 will be sufficient.
- Incidentally with 9kWp on the roof it is borderline criminal not to have a diverter! You're throwing electricity away! A Zappi (or similar) EV charging point can do the same for your EV. It'll only go one way, but it is available now.

Thanks again for information and explanations both. Food for thought then before making a final decision. It's much appreciated.
Either way an FCU appears the way ahead, or an E7 controller for cheaper overnight tariff use. Although unsure if this can then be used with a diverter or whether it's an either or situation. If it's the latter then could I have one element on E7, for Octopus Go, and the second controlled by a diverter?
We do have a Zappi, but I was not aware it could be set up as you describe. It works great at mopping up much of the surplus, but as you correctly point out there are times when the BEV is fully charged. Not that I mind that too much!