Earth Neutral bond for hybrid inverter (again)

[Mattg4321]

A lot of this foreign made/focused equipment comes with instructions not suitable for the uk imo. EV chargers are another one, although slightly better since the uk regs have stabilised somewhat in the last 4 years or so. 
 

Bottom line is you need someone who knows what they are doing to install it. 

[Dillsue]

I think the grid disconnect is done within the inverter as it is with G98/G99 so no external changeover/disconnect needed?? In the second schematic the "on grid home load" will be dead in a power cut and the "load" will be live, fed from the batteries or generator. If the inverter can't sense a stable grid connection it keeps itself disconnected with internal contactors??

 

In terms of installers knowing the requirements for backup power supplies/generators, are they actually covered in the wiring regs to the level that the regs spell it out in black and white and every spark would know exactly how to wire things?? I've always understood it to be a bit of a grey area??

[Nickfromwales]

24 minutes ago, Dillsue said:

I think the grid disconnect is done within the inverter as it is with G98/G99 so no external changeover/disconnect needed?? In the second schematic the "on grid home load" will be dead in a power cut and the "load" will be live, fed from the batteries or generator. If the inverter can't sense a stable grid connection it keeps itself disconnected with internal contactors??

 

In terms of installers knowing the requirements for backup power supplies/generators, are they actually covered in the wiring regs to the level that the regs spell it out in black and white and every spark would know exactly how to wire things?? I've always understood it to be a bit of a grey area??

Half or more of resellers in the solar trade don’t know, so it’s defo a growing concern as PV / batts / EV / paid export as a working combo is defo on the rise. 

[jimseng]

35 minutes ago, Dillsue said:

I think the grid disconnect is done within the inverter as it is with G98/G99 so no external changeover/disconnect needed?? In the second schematic the "on grid home load" will be dead in a power cut and the "load" will be live, fed from the batteries or generator. If the inverter can't sense a stable grid connection it keeps itself disconnected with internal contactors??

That is correct, although I am going to have a manual changeover in the event of a long term power cut so I can include the heavier, grid side loads if I need to.

 

13 minutes ago, Nickfromwales said:

Half or more of resellers in the solar trade don’t know, so it’s defo a growing concern as PV / batts / EV / paid export as a working combo is defo on the rise. 

I have found that so many installations are retro fitted and the backup load side is ignored and the information is therefore limited for people like me installing into a new build. I guess the costs of rewiring to new DBs is prohibitive. Often there seems to be a couple of sockets to charge mobile phones on the load side.

[Nickfromwales]

13 minutes ago, jimseng said:

That is correct, although I am going to have a manual changeover in the event of a long term power cut so I can include the heavier, grid side loads if I need to.

You can do this off the shelf, and as long as you’re not using the induction hob and a 10.5kW electric shower then the inverter will cope whilst you start running around shutting off these big loads.

 

Wouldn’t need the manual changeover then (which is a bit Fred Flintstone nowadays ). 

[SteamyTea]

19 minutes ago, Nickfromwales said:

bit Fred Flintstone

Or better.

 

 

[Dillsue]

37 minutes ago, jimseng said:

That is correct, although I am going to have a manual changeover in the event of a long term power cut so I can include the heavier, grid side loads if I need to.

 

Just check the max power available on the back up output will power the "heavier" loads. The Solis unit I'm thinking of using is a max of 5kw on the back up output so would need a bit of manual load management if we wanted to cook in the winter with the HP running

[jimseng]

2 hours ago, Nickfromwales said:

Wouldn’t need the manual changeover then (which is a bit Fred Flintstone nowadays ). 

Actually I think it does need human intervention, that is why I am planning it this way. If the grid went down while the immersion, heat pump and cooker were going full tilt it would probably take the inverter out (10kw). That would be annoying. This way I can choose which of the heavier devices I want. The biggest down side to it being manual is that if the oven went out then the soufflé would collapse, but I haven't cooked one in 30 years.

[DamonHD]

That is a new and very introspective version of range anxiety - I salute you!

[jimseng]

7 minutes ago, DamonHD said:

range anxiety

I see what you did there. Good one! 😂

[Nickfromwales]

3 hours ago, jimseng said:

it would probably take the inverter out (10kw)

Nope, it would just throw the breaker that the manufacturer installed to stop you from doing that.

 

Then you reset stuff, after turning off the George Foreman Soufflé maker.

[Mattg4321]

I fitted a manual changeover switch to bypass the inverter in the case of the inverter failing, so I can still get power to the circuits fed from the load terminals of the inverter. 
 

Also, you’re only considering the maximum load going through the inverter to the load terminals when the grid is down. What about under normal usage with grid connected? There is likely to be a limit that might be the same as when grid is down. 

[Beelbeebub]

My solution was a bit complicated. 

 

My solax has a "eps" output that stays live in the event of grid failure whilst the grid feed is disconnected (all internal) 

 

As it's an 8kw inverter it will be fine for most loads except if we have a HP or induction hob. 

 

So I have 2 consumer units. One for lighting, sockets etc and the other for heavy loads like the induction hob and (potential) HP. 

 

The "heavy" consumer unit is fed from the grid so will go down in the event of a power cut. The light consumer unit is fed from thr "eps" that stays up. 

 

So in the event of a power cut the induction hob and HP will go down but everything else stays up. 

 

The final bit is both consumer units are fed via manual changeover switches.  This means I can choose to feed both, one or none from the eps (or grid). 

 

If the power cut loops like a long one I can choose to connect the heavy consumer to the eps feed and just be careful.with simultaneous loading. Alternatively, if there is some issue with the inverter unit I can isolate it from the grid and run my house as normal whilst it's fixed. 

[JohnMo]

1 hour ago, Beelbeebub said:

As it's an 8kw inverter it will be fine for most loads except if we have a HP or induction hob. 

Why? Our 6kW inverter runs both, obviously you can't run all the induction hob rings at once.

 

1 hour ago, Beelbeebub said:

So I have 2 consumer units. One for lighting, sockets etc and the other for heavy loads like the induction hob and (potential) HP

Or just go GivEnergy AIO AC coupled, none of this EPS nonsense, it all works as normal in a power cut, that is the whole house electric carries on as normal, as well as the PV. So no change over switches needed the Gateway just does it all automatically. So much so you generally know nothing about power cuts that occur.

[joth]

On 14/02/2026 at 17:41, jimseng said:

Actually I think it does need human intervention, that is why I am planning it this way. If the grid went down while the immersion, heat pump and cooker were going full tilt it would probably take the inverter out (10kw). That would be annoying. This way I can choose which of the heavier devices I want. The biggest down side to it being manual is that if the oven went out then the soufflé would collapse, but I haven't cooked one in 30 years.

An alternative is to have automatic switch over to backup power, but with a long (multiple seconds) blackout period on grid loss before reenergising from backup.

This way most heavy power users will automatically stop and not restart on power restore thereby shedding most the excess loads. All modern, digital controlled ones would; Certainly my ovens, microwave, washing machine and dishwasher, heat pump and hob all do. The immersion is the exception if hard powered on, but if on a PV diverter it's also taken care of. 

Even power tools probably power off too (as operator would have chance to release the trigger before the backup returns) 

 

[Beelbeebub]

10 hours ago, JohnMo said:

Why? Our 6kW inverter runs both, obviously you can't run all the induction hob rings at once.

It's the edge case really - kettle, toaster, microwave (not uncommon at certain times) get us over 6kw with house baseload. Chuck in a couple of hob rings and a HP (it'd a bug house so would be a fairly hefty one) and we could exceed 8kw.

 

That said, the point of the changeover box is we can easily run everything off the eps if we find exceeding 8kw isn't an issue. 

 

As it happens we currently have a fault which was tripping out the Rcbo to the inverter. It effectively gives us a mini power cut. Not a problem as we run on battery backup, but in the current weather we'll eventually run out of battery and then have an actual power cut.  So I just flicked the changeover to grid mode and now it"s fine, although we don't have automatic changeover if there was a real power cut. 

 

10 hours ago, JohnMo said:

just go GivEnergy AIO AC coupled

I did look at givnergy and a couple of other makes that use a seperate changeover box.  For various reasons like lead time, cost, local installers etc I ended up going with a Solax DC coupled system and they use the EPS model, which is basically an integrated changeover system.  All the mucking about with two consumer units etc (thr house already had 2 consumer units so it wasnt any extra work) was just me hedging my bets abouy future loads. It didn't cost much, IIRC the pair of changeover switches were about £75 and the bigger box to house them was £50 more or so.  It did make installation a little easier as it provided a convenient junction box for thr various meter tails. 

[jimseng]

I am planning on exactly what you describe apart from the kitchen ring main which I will have on the grid consumer unit. I will also have a ring main from the load side for the fridge and freezer and a couple of sockets so I can cross plug the kettle mid power cut.

13 hours ago, Beelbeebub said:

Alternatively, if there is some issue with the inverter unit I can isolate it from the grid and run my house as normal whilst it's fixed. 

So you have two changeover switches? I was wondering about the potential inverter failure scenario and whether to put in an extra switch and whether it was worth it.

[Beelbeebub]

4 hours ago, jimseng said:

I am planning on exactly what you describe apart from the kitchen ring main which I will have on the grid consumer unit. I will also have a ring main from the load side for the fridge and freezer and a couple of sockets so I can cross plug the kettle mid power cut.

So you have two changeover switches? I was wondering about the potential inverter failure scenario and whether to put in an extra switch and whether it was worth it.

I'll try and dig out my wiring diagram but here's the box

 

Incoming tails from grid come in, the SPD and it's breaker are connected there. The love and neutral the head via the SolaX RCD and the live via the MCB out to the solax. They also go into the "grid" input of each changeover switch. The output of each changeover switch then goes to each CU. 

 

The eps love and neutral come back from the unit and connect to tge other input of the changeover switch (the live via the eps breaker) 

 

Currently CU2 is connected to the grid, the inverter can power it but it will go down in the event of a power cut. 

 

CU1 is fed via the EPS and stays up in the event of a power cut. 

 

(not shown are some Henley blocks below to split the connections)

[jimseng]

@Beelbeebub
A wiring diagram would be most interesting if you can find it, although I am sure I can work it out.

[Mattg4321]

18 hours ago, JohnMo said:

Why? Our 6kW inverter runs both, obviously you can't run all the induction hob rings at once.

 

Or just go GivEnergy AIO AC coupled, none of this EPS nonsense, it all works as normal in a power cut, that is the whole house electric carries on as normal, as well as the PV. So no change over switches needed the Gateway just does it all automatically. So much so you generally know nothing about power cuts that occur.

It’s horses for courses really as DC coupled is lower up front cost and slightly more efficient as no need to convert DC to AC and back to DC