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I am getting a qualified electrician to do the AC side of my PV. I'm sourcing all the components and want to check what I'll need.

I don't think I need a Henley block to wire in the inverter as I have spare circuits on my consumer unit.
Is that correct?

Do I need a separate breaker between the inverter and the consumer unit?

For the Backup AC output of the Inverter do I need an isolator in the loft next to the circuit breaker?
I will have a SP3T change over switch next to the consumer unit so that the critical load consumer unit can be switched if say the Inverter had to be removed.
(Goodwe inverters instructions say this is a requirement though I'm hoping to collect a Solis inverter on Monday and Solis don't mention one)

The inverter installation manual talks of using round AC cables. It will be in the loft so IP rating is not a concern, can I use standard flat twin and Earth?

Schematic:

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pm I am getting a qualified electrician to do the AC side of my PV. I'm sourcing all the components and want to check what I'll need.

I don't think I need a Henley block to wire in the inverter as I have spare circuits on my consumer unit.
Is that correct?

A Henley block is the wrong type of connector for something as low power as this, as they are usually for fatter cables (meter tails typically). No need for any interconnection, it's fine to connect the cable from the AC isolator directly to the RCBO or MCB in the consumer unit (it does need to have RCD protection, so either on an RCBO or an MCB protected by an RCD)

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmDo I need a separate breaker between the inverter and the consumer unit?

Yes, normally this would be an AC DP isolator, often fitted adjacent to the inverter.

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmFor the Backup AC output of the Inverter do I need an isolator in the loft next to the circuit breaker?

Depends how the inverter does the AC backup. Some have an internal changeover relay, so the same AC output serves both purposes and there is no need for any further isolation. Some have two AC connections, a normal grid power one and a second backup power one. If you have one of the latter then both need isolators, not just the grid one.

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmI will have a SP3T change over switch next to the consumer unit so that the critical load consumer unit can be switched if say the Inverter had to be removed.
(Goodwe inverters instructions say this is a requirement though I'm hoping to collect a Solis inverter on Monday and Solis don't mention one)

The topic of grid and backup switching and isolation can get complex, as unless your installation has TT earthing then you need to be able to provide a TT earth in backup mode, as the chances are the supplier's incoming earth will not be present in a power cut. You may also need to arrange for the earth and neutral to be linked in backup mode, as not all inverters do this. In theory you can run the back up supply as IT, with neither AC conductor connected to earth, but it's likely that most electricians won't have come across an IT supply and may not feel happy signing such an arrangement off.

My solution was simplified as our installation already had TT earthing, so all I needed to do was make sure that the neutral and earth are linked when the inverter is in backup mode. I have a feeling that there may be some info on whether the Solis connects neutral to earth in backup mode in another thread here, might be worth a look around to find posts about this.

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmThe inverter installation manual talks of using round AC cables. It will be in the loft so IP rating is not a concern, can I use standard flat twin and Earth?

T&E is fine in the loft, no need for any greater protection. Only slight issue may be the cable glands on the inverter. Ours came with oddball glands that accepted three separate conductors, which would be against the regs to use here, so I swapped them for round cable glands and used 2.5mm² flex to connect to a junction box. If you need round rigid cable to fit the inverter glands then NYY-J cable would be fine, or you could just use a short length of flex to connect to the AC isolator and T&E from there.

Only thing to add is along the lines that OGB has already outlined.

You show a SP3T change over switch for your critical loads.

That suggests your only switching the live which leaves your neutral still connected to the PME in a standard TNCS installation. So in a planned blackout that would be OK because you would still have a neutral to earth connection. But if you lost power because of a cable fault in the street, you may lose the PME, therefore the recommendation is to install a local earth rod to keep the earth (and neutral) wires as close to earth voltage as possible.

Oldgreybeard wrote: ↑Sat Nov 26, 2022 4:51 pm

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pm I am getting a qualified electrician to do the AC side of my PV. I'm sourcing all the components and want to check what I'll need.

I don't think I need a Henley block to wire in the inverter as I have spare circuits on my consumer unit.
Is that correct?

A Henley block is the wrong type of connector for something as low power as this, as they are usually for fatter cables (meter tails typically). No need for any interconnection, it's fine to connect the cable from the AC isolator directly to the RCBO or MCB in the consumer unit (it does need to have RCD protection, so either on an RCBO or an MCB protected by an RCD)

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmDo I need a separate breaker between the inverter and the consumer unit?

Yes, normally this would be an AC DP isolator, often fitted adjacent to the inverter.

I think you misunderstood me, sorry if I'm using the wrong terminology. I'm planning on having a rotary isolator in the loft by the inverter(as per the schematic above) but do I also need a 32Amp Circuit Breaker (Fuse) in the loft? It will at the Consumer unit go through an MCB.

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmFor the Backup AC output of the Inverter do I need an isolator in the loft next to the circuit breaker?

Depends how the inverter does the AC backup. Some have an internal changeover relay, so the same AC output serves both purposes and there is no need for any further isolation. Some have two AC connections, a normal grid power one and a second backup power one. If you have one of the latter then both need isolators, not just the grid one.

Yes Two AC connections as per the schematic.

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmI will have a SP3T change over switch next to the consumer unit so that the critical load consumer unit can be switched if say the Inverter had to be removed.
(Goodwe inverters instructions say this is a requirement though I'm hoping to collect a Solis inverter on Monday and Solis don't mention one)

The topic of grid and backup switching and isolation can get complex, as unless your installation has TT earthing then you need to be able to provide a TT earth in backup mode, as the chances are the supplier's incoming earth will not be present in a power cut. You may also need to arrange for the earth and neutral to be linked in backup mode, as not all inverters do this. In theory you can run the back up supply as IT, with neither AC conductor connected to earth, but it's likely that most electricians won't have come across an IT supply and may not feel happy signing such an arrangement off.

My solution was simplified as our installation already had TT earthing, so all I needed to do was make sure that the neutral and earth are linked when the inverter is in backup mode. I have a feeling that there may be some info on whether the Solis connects neutral to earth in backup mode in another thread here, might be worth a look around to find posts about this.

The Inverter has built in automatic switch over so a changeover switch is only needed if for some reason you need to totally bypass the inverter.
Double Pole three position switches seem easier and cheaper to buy than single pole so I could easily switch Neutral as well as live? Or have I misunderstood?

The Earthing is PME. (Our power is overhead)

ChrisJEvans wrote: ↑Sat Nov 26, 2022 4:28 pmThe inverter installation manual talks of using round AC cables. It will be in the loft so IP rating is not a concern, can I use standard flat twin and Earth?

T&E is fine in the loft, no need for any greater protection. Only slight issue may be the cable glands on the inverter. Ours came with oddball glands that accepted three separate conductors, which would be against the regs to use here, so I swapped them for round cable glands and used 2.5mm² flex to connect to a junction box. If you need round rigid cable to fit the inverter glands then NYY-J cable would be fine, or you could just use a short length of flex to connect to the AC isolator and T&E from there.

Thanks for the answers Oldgreybeard & nowty you help is very much appreciated.

ChrisJEvans wrote: ↑Sat Nov 26, 2022 9:58 pm The Inverter has built in automatic switch over so a changeover switch is only needed if for some reason you need to totally bypass the inverter.
Double Pole three position switches seem easier and cheaper to buy than single pole so I could easily switch Neutral as well as live? Or have I misunderstood?

The Earthing is PME. (Our power is overhead)

In that case no comment from me regarding the earthing as it depends on your existing installation and how your inverter deals with the change over. There are some threads about it on the forum and if you look you will see its not straight forward at all.

Indeed earthing, and the need for an earth-neutral link when in backup mode (but not in grid mode) seems to be a right old can of worms, with no "one size fits all" solution.

It seems that many inverters, especially Chinese ones, don't connect the neutral to earth when in backup mode, and few seem to make any reference to how a protective earth should be provided when the grid fails, either.

I think the foolproof solution for earthing is to just forget about using either a PME or TNS earth (i.e. one that comes in on the supply cable) and use a TT arrangement with a local earth electrode. Not always practical to do this, though, and it also means adding a 100mA Type S RCD on the incoming supply, which creates a bit more work.

The other option is to have an earth electrode that's only used for the backup supply. The regs allow this to be paralleled to the incoming earth, but there is still the possibility that an incoming PME could rise to a high voltage under fault conditions and the relatively high resistance of the earth electrode wouldn't do much to counter that.

The final option is to switch the earth from the PME or TNS to an earth electrode when the backup supply comes on. This could be done with another pole on the earth-neutral relay, perhaps.

PME was installed as the earthing stake (IIRC about 70 ohms) caused the control panel of a fridge freezer problems.
I think the earthing stake is still connected.

I'll use a 2pole swapover switch so L & N will be switched. I don't expect to ever have to use the switch.

The relay for the AC backup is in the Inverter and I doubt I could change it without invalidating the warranty.

I think oldgreybeard’s suggestion of a separate electrode is the best idea, similar to if you used a petrol/diesel genny.

All EPS must have a consumer earth rod.

The floating neutral class 2 socket is now heavily discouraged. Even more so if your inverter doesn't have the IEC cert for true UPS.

ChrisJEvans wrote: ↑Sun Nov 27, 2022 3:44 pm
I'll use a 2pole swapover switch so L & N will be switched. I don't expect to ever have to use the switch.

For a switch you don't expect to use these https://www.ukelectricalsupplies.com/fu ... busbar.htm are a lot cheaper than the industrial ones in their own enclosures.