The right inverter for battery storage and some other Qs

[ducabi]

Can you sketch an actual wiring diagram showing the incoming main, old consumer unit with feed to the inverter and also wiring to the new "mini" consumer unit? I ask because from my interpretation of your description it seems the new "mini" C.U. is connected to the EPS output of the inverter via the MCB, but the C.U. is also connected to the grid via the main switch and the "Henley" block. If so then this is totally wrong and dangerous as the inverter will try to backfeed into the grid in EPS mode when it must be isolated from it.

Apologies if I have misunderstood your description.

Instruction from electrician for EPS: switch off grid isolator (1) + switch on EPS switch (2) + switch off DP in New mini CU, and then EPS works. I tested it by switching off isolator next to the meter.

Diagram.
Inverter gets power from Main CU (through MCB 32 Type B behind RCD 63A, 30mA Type AC).
Then when it feeds mini CU through EPS it goes through MCB only and.
I'm not entirely sure how and WHY new mini CU is linked to main CU because there are too many cables to trace it.

[Oldgreybeard]

Not sure that diagram is right, TBH. If the EPS for your inverter works in the same way as the one for my Sofar ME3000Sp, then it needs a changeover contactor to switch the maintained supplies from grid power to EPS power. This is key, as without it there is a serious risk that it might try to backfeed the grid, which is both dangerous (for those working to fix any outage) and will overload the inverter EPS output. This is the diagram from the ME3000SP manual that shows how the contactor needs to be wired:

Sofar EPS.jpg (61.94 KiB) Viewed 1742 times

I used a more compact 16A changeover contactor for my system, that fits within the maintained supply CU at the left (the treatment plant was being serviced when this photo was taken, hence the reason its RCBO is off):




If your second CU is doing the same function as mine, supplying power to the maintained circuits that are on during a power cut, then the wiring needs to be similar. Not sure if it helps, but this is a detailed wiring diagram of that small CU on my system:

Backup CU wiring.jpg (153.05 KiB) Viewed 1742 times

The key thing is that the only source of power to that essential circuits CU is from either the 20A RCBO in the main CU, or the inverter EPS output. There is no direct connection between it and the grid at all, and must not be, as the contactor is a key safety isolation device to stop the grid ever being back powered from the inverter.

[Stinsy]

Am I right that you have a 16A changeover contactor protected by a 20A RCBO?

[Oldgreybeard]

Am I right that you have a 16A changeover contactor protected by a 20A RCBO?

Yes, but that's fine, as contactor ratings are long duration carry loads, their short duration carry load is a fair bit higher. That contactor is rated to carry 128A for 10s at 40°C, 40A for 30s at 40°C, so is OK with 20A B curve RCBO protection. (Edited to add:)This is from the datasheet for the contactor used:

Contactor rating.jpg (46.63 KiB) Viewed 1719 times

These are the trip times for a 20A B curve RCBO with a 40A overload. It will trip after between 5 and 15 seconds at 40A, and the contactor is rated to carry 40A for 30 seconds at 40°C, so there is a safe enough margin IMHO:

B curve 40A trip times.jpg (35.23 KiB) Viewed 1710 times

Bit of a moot point, anyway, as the inverter can only output around 13A and can only draw about the same, plus there's a 16A MCB on both the grid and load circuits at the inverter end. Over current protection is mostly about protecting cables from overheating, anyway, and the lower rating of the RCBOs in the small CU looks after that If there were to be multiple overloads that didn't trip the small CU RCBOs then the 20A RCBO would trip within about 20 seconds at 40A, well within the 30s that the contactor will safely carry 40A for.

[marshman]

Which is why I queried it in my post. There is no change over switch and the EPS is feeding in to the CU via an MCB which is totally wrong and dangerous in that it is too easy for one of the isolators to be left on and the EPS feed into the grid. Also there has been no mention of the earthing situation.

[ducabi]

Which is why I queried it in my post. There is no change over switch and the EPS is feeding in to the CU via an MCB which is totally wrong and dangerous in that it is too easy for one of the isolators to be left on and the EPS feed into the grid. Also there has been no mention of the earthing situation.

I could be wrong but if I switch off grid feeding to inverter, then switch off main switch in mini CU, then by switching ON EPS switch everything stays outside of grid, isnt it?

Earthing was mentioned couple pages ago, straight after installation. Basically that electrician said it's not required because it will be supplied during blackout. But I will have earth rod installed by my other electrician.

[Oldgreybeard]

Which is why I queried it in my post. There is no change over switch and the EPS is feeding in to the CU via an MCB which is totally wrong and dangerous in that it is too easy for one of the isolators to be left on and the EPS feed into the grid. Also there has been no mention of the earthing situation.

I could be wrong but if I switch off grid feeding to inverter, then switch off main switch in mini CU, then by switching ON EPS switch everything stays outside of grid, isnt it?

Earthing was mentioned couple pages ago, straight after installation. Basically that electrician said it's not required because it will be supplied during blackout. But I will have earth rod installed by my other electrician.

From the diagram there doesn't seem to be anything isolating the grid from the mini CU, that seems to be permanently connected via the tails to the Henley block.

The electrician is wrong about the earthing, too. If you have the most common forms of UK supply, either TN-C-S/PME or TN-S, then the earth is provided via the incoming cable from the street. If there is a power cut then there is a very good chance that the earth provided via this cable will not exist, as very often the earth/neutral is the first conductor to break in the event of cable damage (because it's always on the outside of the supply cable, so the first bit to get cut through accidentally). If the supply is TN-C-S/PME, then you may be lucky and have the cable break on the supplier side of an intermediate earth electrode on the supply, but I don't think you can rely on that being the case.

[nowty]

I could be wrong but if I switch off grid feeding to inverter, then switch off main switch in mini CU, then by switching ON EPS switch everything stays outside of grid, isnt it?

Sorry I have not been following this very well.

Are you saying your going to manually enable the EPS on the inverter after isolating everything manually ?

i.e, the EPS will be disabled as the default position in normal operation.

[ducabi]

Sorry I have not been following this very well.

Are you saying your going to manually enable the EPS on the inverter after isolating everything manually ?

i.e, the EPS will be disabled as the default position in normal operation.

Not sure if it matters whether EPS mode in inverter settings is enabled or disabled in this case but the procedure is to go to garage and start switching things OFF and ON. Otherwise EPS won't work.
I tested it by switching off isolator switch next to meter and without doing the above there is no power to any of the circuits.

[Oldgreybeard]

Not sure if it matters whether EPS mode in inverter settings is enabled or disabled in this case but the procedure is to go to garage and start switching things OFF and ON. Otherwise EPS won't work.
I tested it by switching off isolator switch next to meter and without doing the above there is no power to any of the circuits.

The concern is that from your diagram, there is no way to ever isolate the maintained supply CU from the grid. When the EPS isolator switch is on then the inverter powers the grid, via the red arrows I've added to your diagram:

Edited wiring diagram.jpg (24.45 KiB) Viewed 1721 times