FoxESS Community - Owners & Installers Forum

Hi Community.
I'm in the process of having a KH10 and 5.76kWh ECS2900 battery system installed and think that my installer may be misleading me slightly. The inverter and battery were installed this week, with 13.33kW of solar (weather dependant.....) next week.
I've a question for anyone with knowledge of UK wiring regs that can maybe give me some advice that I can pass on to my installer in good faith, I don't want to come off as too pushy or argumentative, since they are the 'experts'.

Currently the inverter AC input flex cable to generation meter is 6mm2 (or maybe 8 - it doesn't have any markings on the cable, but measures less than 5mm diameter). From the meter to AC isolator through to dist board is 10mm2. The dist board then has a 40A breaker.
From a cable protection point of view, this may(?) be correct, but then I will never be able to export 10kW from my inverter without tripping the 40A breaker. I explained this to the electrician and he said that I'll never do more than 7kW solar or battery export with my setup.
After a bit of back and forth and me explaining that this inverter is designed to export up to 10kW to meet my local demand from both battery and solar if necessary, they have decided to increase the cable size to 10mm2 all the way to the inverter and install a 50A breaker. They said that 10kW is around 42A, so the circuit is fine if they uprate it to 50A.
I've explained that the inverter is rated to 48A output (on the name plate!) and the installation manual says 63A breaker and suitable (13-16mm) cable.

If my understanding of UK wiring regs is correct, if the nameplate of an electrical appliance says 48A, then the circuit should be rated to a certain % (10%?) above that - despite my installer saying that 10kW is only 42A (at perfect voltage and power factor).

So the short question is; should I be happy that they have agreed to move to 50A and leave it like this, or should I push to get the circuit rated to 63A?

Thanks for any input.

This could be a long answer particularly if you get into UK wiring regs, so i'll keep it short - Fox ESS recommend that you fit 8mm-10mm cable with a 63A breaker - and for this inverter that is what you should have (see attached taken from the KH installation manual).

EPS is the emergency power supply option which can power critical loads in the event of grid failure - you haven't mentioned that and it's a whole heap of wiring, changeover switches and earth rods (and extra expense). Most UK solar installs don't have this for this reason.

The UK grid is 230V +10%, -6% i.e. 253V - 218V so the possible range is 39A to 45.7A and given the load nature of grid tied inverters a 50A breaker would be undersized - although admittedly you might never draw (or export) that much power so you 'may' not see a problem.

If you have a DNO limit that will limit what you can export (7kW?), but your inverter is capable of outputting 10kW on the AC side if you have enough panels to generate it a 10kW house load could easily be met by the inverter - hence it must be wired for that.

I'll just mention this now, so you are aware - with 2 ECS2900 batteries the maximum output they can support (taking their nominal voltage of 115V dc) is 5.75kW - the maximum power they can meet is limited by their 50A max current and so battery stack voltage dictates the power (and the more batteries the higher the voltage).
5.75kW is a reasonable amount of power and as any excess house load would be topped up from the grid it will all work just fine - but if you absolutely wanted to use the batteries exclusively to power the full 10kW house load you would need to consider getting 2 more batteries (which either you or your installed can add yourself)

Hi Dave,

Thanks for your input on this. I hadn't read or understood the manual completely, so yes it should really be 8-10mm cable and 63A breaker for non EPS. I've double checked the inverter name plate and it is 45.7A as you said, so I'm not sure where I got 48 from.
I did pay the extra price from my installers for a 16A EPS socket on my install as I have a submersible pump (and more importantly? home automation stuff) that needs to protect my property from floods in the event of a power cut. I hadn't thought of the implications of this.
Interestingly, the manual you link above differs slightly from the quick install guide that the electrician has left in the box, this says 100A micro-breaker if the EPS or battery charge from gird is used. Do you happen to know what the wording 'or use on grid power to charge' means? Does this suggest that with battery and no EPS, the inverter can charge the battery with more than 10kW. Or is this just because I could 'theoretically' (I was aware as you mention above that my existing batteries are limited to 50A at nominal DC voltage) charge with 10kW and have a load connected to EPS plug at the same time?

Also, I wasn't made aware of any g99/g100 limitations by the installer since they have managed all this, I just assumed I could use my 10kW inverter to its maximum e.g. 5kW solar + 5kW battery if my house demand (or forced discharge?) needed it.

I guess I'll need to at minimum ask for 63A, but also mention to the installer that at some stage it could lead to nuisance tripping if I buy more batteries and end up charging them and running my flood pumps at the same time.
I'm also a bit worried about the 'whole heap of wiring, changeover switches and earth rods' involved with an EPS port - My installer has just put a small 100A board with 16A breaker and socket fed from it. I guess I'll start looking into what this should look like and have a few more discussions with them if necessary.

I should point out that I do get on with my installers and chose them based on meeting a few of their actual customers and seeing their installs, so I completely trust them, but think they may not quite have got this one quite right yet.

Thanks again.

Will

I think you’ll be just fine with a 63A breaker.

The complexity stems from the fact that you ‘could’ power your entire house off EPS if you chose to wire it that way, and when it is in that mode you could be taking 10kW from grid for the EPS loads and also charging the battery at the same time - in your case the max battery charge is 5.75kW so a 15.75kW draw from grid.

But that isn’t the way your system will be wired, as you say it’s only a protected double socket for critical items - the rest of the house is running off the normal consumer unit.

I may have misunderstood when I said your DNO limit of 7kW as I thought that’s why the electrician may have been saying it will only be 7kW max inverter - if you are lucky your G99 limit could be the full 10kW you’ll have to double check.
But whatever the DNO limit is, that is only for export you can use the full 10kW capabilities in the house - it’s only your export that is limited by G99.

There is a thread on this forum talking about the various EPS options, you will probably have the easiest as the KH inverter will automatically bond N-E on the EPS when the grid fails, but the reason for installing an earth rod on the earth to the EPS circuits is because if your incoming supply is severed you would have no earth in the house otherwise.

If you are short on sleep these 2 posts explain and cover the EPS subject

This first one explains the various options
viewtopic.php?t=52


The second the problem with bonding and earthing (note earlier inverters did not have a P-NE bonding relay for the EPS, yours does which simplifies that).

viewtopic.php?t=763