The right inverter for battery storage and some other Qs

[Oldgreybeard]

Yes, only the inverter MCB needs to swapped out for an RCBO. The MCB on the SPD is fine, they are supposed to only have MCB protection.

Really hard to tell if that's 4mm² cable, TBH. Also odd that it doesn't look like flex, as I'm pretty sure flex is about the only cable type that will easily fit the terminals in the inverter. Is there a cable joint somewhere in the trunking, perhaps?

[ducabi]

Yes, only the inverter MCB needs to swapped out for an RCBO. The MCB on the SPD is fine, they are supposed to only have MCB protection.

Really hard to tell if that's 4mm² cable, TBH. Also odd that it doesn't look like flex, as I'm pretty sure flex is about the only cable type that will easily fit the terminals in the inverter. Is there a cable joint somewhere in the trunking, perhaps?

I've just read that 4mm2 is not same as 4mm diameter. So the cable is 1.6mm2 i think (4mm diameter). Below is the picture of that cable and where it comes from. Is it flex? Is that ok it's 1.6mm2?

[Oldgreybeard]

I've just measured the outside diameter of a bit of 4mm² single and it's about 4.05mm to 4.1mm in diameter. I've also just measured a bit of 2.5mm² single and that's about 3.5mm to 3.55mm. Not sure that helps at all, but the cable going into the 16A RCBO next to the MCB looks to be the same size in the photo, and that is most likely to be 2.5mm².

Really hard to say one way or the other whether the cable is 2.5mm² or 4mm². Personally I'd play safe and just fit a 20A RCBO. That would be safe with either 2.5mm² or 4mm² cable.

[ducabi]

I've just measured the outside diameter of a bit of 4mm² single and it's about 4.05mm to 4.1mm in diameter. I've also just measured a bit of 2.5mm² single and that's about 3.5mm to 3.55mm. Not sure that helps at all, but the cable going into the 16A RCBO next to the MCB looks to be the same size in the photo, and that is most likely to be 2.5mm².

Really hard to say one way or the other whether the cable is 2.5mm² or 4mm². Personally I'd play safe and just fit a 20A RCBO. That would be safe with either 2.5mm² or 4mm² cable.

If i trace the cable in trunking shall I be able to read cable parameters on it? What's the worst can happen if I fit 20A RCBO to 4mm2 cable?

[Oldgreybeard]

I've just measured the outside diameter of a bit of 4mm² single and it's about 4.05mm to 4.1mm in diameter. I've also just measured a bit of 2.5mm² single and that's about 3.5mm to 3.55mm. Not sure that helps at all, but the cable going into the 16A RCBO next to the MCB looks to be the same size in the photo, and that is most likely to be 2.5mm².

Really hard to say one way or the other whether the cable is 2.5mm² or 4mm². Personally I'd play safe and just fit a 20A RCBO. That would be safe with either 2.5mm² or 4mm² cable.

If i trace the cable in trunking shall I be able to read cable parameters on it? What's the worst can happen if I fit 20A RCBO to 4mm2 cable?

A 20A RCBO is perfectly safe with any cable of 2.5mm² or greater cross section, and is fine for the maximum current that the inverter can deliver or use, so is a safe option. Be interesting to know if there is a joint somewhere, though. My gut feeling is that the joint may be the wagos that were poking out of the trunking. Chances are the flex from the inverter changes to singles at that point, perhaps, or maybe the joint is at the isolation switch.

[ducabi]

Be interesting to know if there is a joint somewhere, though. My gut feeling is that the joint may be the wagos that were poking out of the trunking. Chances are the flex from the inverter changes to singles at that point, perhaps, or maybe the joint is at the isolation switch.

Wagos were for PV meter i think. What's the issue with flex/non-flex cables? I'll remove trunking and check how it goes.

[Oldgreybeard]

Be interesting to know if there is a joint somewhere, though. My gut feeling is that the joint may be the wagos that were poking out of the trunking. Chances are the flex from the inverter changes to singles at that point, perhaps, or maybe the joint is at the isolation switch.

Wagos were for PV meter i think. What's the issue with flex/non-flex cables? I'll remove trunking and check how it goes.

The only issue is getting non-flex cable to terminate at the inverter. Space is tight inside the cover over the terminal blocks and when I tried to use a bit of 2.5mm² NYY-J cable I found that it was just too stiff to bend easily when the cover was being slid back on. I didn't like the way the wires were straining the terminals, so I swapped the NYY-J (which has rigid cores) for 2.5mm² SY cable, which is flexible, so didn't strain the terminals when dressing the cables in to the cover.

This is what makes me think there may be a joint somewhere, as the wire going into the MCB doesn't look like a core from flex.

[ducabi]

The only issue is getting non-flex cable to terminate at the inverter. Space is tight inside the cover over the terminal blocks and when I tried to use a bit of 2.5mm² NYY-J cable I found that it was just too stiff to bend easily when the cover was being slid back on. I didn't like the way the wires were straining the terminals, so I swapped the NYY-J (which has rigid cores) for 2.5mm² SY cable, which is flexible, so didn't strain the terminals when dressing the cables in to the cover.

This is what makes me think there may be a joint somewhere, as the wire going into the MCB doesn't look like a core from flex.

I think it's 4mm2 flex cable based on what it says on it (supreme flex 50525-2-21 304).

In terms of how they run.
1) 1st cable goes to grid switch and from there it goes to main CU which has type B MCB 32A and RCD in front of it (together with other circuits). When i switch it off the inverter goes to EPS mode.
2) 2nd cable goes to EPS switch and then to new mini CU as per the previous pictures.

Does it sound ok? If there is no RCBO for inverter in new mini CU but the power to inverter goes from main CU through MCB->RCD->AC switch, does it mean I need RCBO in new mini CU only for EPS?

[Oldgreybeard]

I think it's 4mm2 flex cable based on what it says on it (supreme flex 50525-2-21 304).

Sounds as if the flex is 4mm² from that description. That number refers to H07RN-F or possibly H05RN-F flex, which is fine.

In terms of how they run.
1) 1st cable goes to grid switch and from there it goes to main CU which has type B MCB 32A and RCD in front of it (together with other circuits). When i switch it off the inverter goes to EPS mode.
2) 2nd cable goes to EPS switch and then to new mini CU as per the previous pictures.

Does it sound ok? If there is no RCBO for inverter in new mini CU but the power to inverter goes from main CU through MCB->RCD->AC switch, does it mean I need RCBO in new mini CU only for EPS?

Not a good idea to have RCDs in series, but only because of the possibility of nuisance tripping causing the "wrong" RCD/RCBO to trip if there is a fault (i.e. the main RCD could trip and take out all the circuits, rather than the RCBO trip only taking out the faulty one). It's not specifically against the regs, and isn't usually unsafe, but the regs do recommend that there be selectivity with series RCDs/RCBOs, which in practice means the upstream RCD being a 100mA Type S whilst all the downstream circuits are protected with 30mA Type A RCDs/RCBOs. May not be anything you can easily do to resolve this, though, as you cannot have a 100mA Type S RCD protecting final circuits, they must always be upstream of 30mA RCDs/RCBOs.

If it were me then I would definitely swap the 32A MCB for a 32A or 20A RCBO (can't see any reason not to fit a 20A TBH) and I'd also re-jig the sub-main supply so that it only has an MCB protecting it at the main CU, and is not going through an RCD that is most probably also feeding other circuits. That gets rid of the selectivity problem and makes every circuit properly independently protected.

[marshman]

The only issue is getting non-flex cable to terminate at the inverter. Space is tight inside the cover over the terminal blocks and when I tried to use a bit of 2.5mm² NYY-J cable I found that it was just too stiff to bend easily when the cover was being slid back on. I didn't like the way the wires were straining the terminals, so I swapped the NYY-J (which has rigid cores) for 2.5mm² SY cable, which is flexible, so didn't strain the terminals when dressing the cables in to the cover.

This is what makes me think there may be a joint somewhere, as the wire going into the MCB doesn't look like a core from flex.

I think it's 4mm2 flex cable based on what it says on it (supreme flex 50525-2-21 304).

In terms of how they run.
1) 1st cable goes to grid switch and from there it goes to main CU which has type B MCB 32A and RCD in front of it (together with other circuits). When i switch it off the inverter goes to EPS mode.
2) 2nd cable goes to EPS switch and then to new mini CU as per the previous pictures.

Does it sound ok? If there is no RCBO for inverter in new mini CU but the power to inverter goes from main CU through MCB->RCD->AC switch, does it mean I need RCBO in new mini CU only for EPS?

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.