Posted by: @transparent

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Posted by: @transparent

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Equally, an electrician will understand that the Change-over switch must not be positioned within a CU alongside MCBs supplying other circuits.
We're discussing a situation where the change-over switch is in a separate enclosure, for reasons which I hope are now obvious.

Not to me I must say.  Whats the additional risk exactly that is not covered by a label. 

I keep in mind the following two checks:

a: by modifying a design/schematic am I increasing safety (lowering risk) ?

b: is my strategy providing flexibility without compromising system resilience ?

On this forum we are already advocating the use of a separate double-pole isolator on the incomer wires to a CU.

It's not mandatory.

But it allows an electrician to work in a CU without the 240v input to the Main Switch being live.

In your case @jamespa the Changeover Switch in a separate enclosure would also provide that functionality via a Centre-Off position.

Placing a switch (that already requires a Warning Label) inside that CU increases the risk level,
and it does so beyond the level normally met by a double-pole Main Switch with a 240v incomer. 

There is a reason that "Danger 440v" and "Danger 415v" signs exist.
They demonstrate a commitment to reduce risk under ISO 7010, and the Health and Safety at Work Act.

And they comply with the IET Wiring Regulations (BS7671), section 514.10.1

[...] a warning notice must be installed where a nominal voltage exceeding 230 V to earth (or 400 V between lines) exists
within an enclosure or on equipment, particularly where such a voltage would not normally be expected.

Posted by: @jamespa

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Furthermore if the ups and downs of the grid as it switched on are likely to damage electronics, which you suggest above, then everyone without an inverter faces this risk.

Not quite.

A hybrid inverter is itself a generator.
It can create harmonics and spikes locally (within the home).
Those don't have the benefit of being suppressed by the capacitance of the long length of cable between the home and a local substation.

You really want the grid mains to be stable before offering it as the supply to an inverter.

Posted by: @transparent

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Posted by: @batpred

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One thing to be aware is that this 440V/different phases in various sockets should not normally happen, not with this Solis S6 hybrid.

We're discussing 440v being present inside the enclosure which houses the change-over switch.

There needs to be a warning.
An electrician can then be sufficiently aware of the situation to ensure that the cover of that enclosure is in place before switching the house back on
following whatever work or tests might have been carried out.

The regulation mandates labels indicating that there are multiple generation sources in the site. My installation has this, but for better awareness (and for eventual future residents), we will add 4xxV labels to the switch and isolator. 

Posted by: @transparent

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In your case @jamespa the Changeover Switch in a separate enclosure would also provide that functionality via a Centre-Off position.

That would make sense; the 2 off mcbs would need to go in the same enclosure so the challenge might be to find the right kit of parts!  A quick search didn't turn up any din mounted 4 pole 100A changeover switches with centre off other than an unbranded Chinese one.  Hopefully one exists!

Posted by: @batpred

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The regulation mandates labels indicating that there are multiple generation sources in the site.

Would you care to say which regulation you're referring to?

In my quest for safe practice I am often 'fed' relevant clips on YouTube.

This one from eFIXX about possible types of Neutral and Earthing faults is informative.

On this forum I don't think we can conjecture all the possible fault scenarios which inverter wiring should provide a level of protection against.
But videos like this give me sufficient 'feel' for the subject that I find myself erring on the side of reducing risk.

That seems the right way to be going.

Posted by: @transparent

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Posted by: @batpred

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The regulation mandates labels indicating that there are multiple generation sources in the site.

Would you care to say which regulation you're referring to?

When I was looking for the regs for labelling when introducing an inverter able to export, I started with some of the questions present in the G99 commissioning form like: 

• Generator’s Installation satisfies the requirements of BS7671 (IET Wiring Regulations). 
• Suitable lockable points of isolation have been provided between the PGMs and the rest of the Generator’s Installation. 
• Labels have been installed at all points of isolation in accordance with EREC G99. 

As I wanted to make sure the electrician would have the required labels, I purchased a set of labels of the type suitable for a PV installation. A subset of these were then applied in and around the consumer unit and inverter. Something like the below: 

For guidelines including an overview of labelling, this IET article seems relevant.  Ultimately, qualified electricians have access to the current regulations. 

Posted by: @transparent

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On this forum I don't think we can conjecture all the possible fault scenarios which inverter wiring should provide a level of protection against.
But videos like this give me sufficient 'feel' for the subject that I find myself erring on the side of reducing risk.

That seems the right way to be going.

Yes and it can be very difficult to give advice without assessing all the site conditions. The video you shared seems to focus on risks related to earthing, but I appreciate it is not easy to find one describing specific islanding inverter topics.  

My approach has been that, given how few domestic electricians have extensive experience with inverters, etc, it helps readers to become informed owners. They may be able to do some of the planning. Whilst using an electrician is essential, more knowledge helps. I do not even envision trying to understand all the extensive considerations that MCS would impose on this type of installation work, in terms of ideal calculations of ROI, etc (mainly because, at the end of the day, MCS does not provide a guarantee themselves..).  

I’m quite intrigued by sodium ion batteries over lithium. Does anyone on the forums have one running at home?

Posted by: @editor

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I’m quite intrigued by sodium ion batteries over lithium. Does anyone on the forums have one running at home?

We discussed this recently in the Sodium battle thread, @editor . There are very few systems available to consumers and they do not look very mature. Inverters able to handle sodium are significantly different, so the initially available systems are not modular (like commonly available lithium based systems).

The current low starting price for lifepo4 batteries and the expectation (given the relative cost of lithium vs sodium) that sodium based would be lower cost does not indicate a fast uptake...

Posted by: @editor

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I’m quite intrigued by sodium ion batteries over lithium.

See what I posted over on that other topic:

Posted by: @transparent

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Prices are very similar to FePO4 but the nominal cell-voltage is slightly lower (3.1v instead of 3.2v)
and the operational range is much wider (1.5v - 4.1v).

Suppose your Na-ion battery was to supply a heat-pump which required 3kW (at 240v)...
and that you had 16 cells in series.

A fully charged sodium battery with cells at 4.1v would be operating at 65½v and delivering 45A to the inverter.

As it reaches 10% capacity, the battery voltage would've fallen to about 48v (3.0v per cell – see green curve below)

At 48v the inverter would now be drawing 62A current from the sodium battery.

Although the sodium battery would happily allow you to use that last 10% of capacity, the increased current you'd need means that it's unviable.
The cabling would need to be thicker to carry currents in excess of 100A, and the BMS capable of handling that too.

For that reason a system based on sodium ion chemistry requires inbuilt cut-offs to limit the current,
as opposed to Li-ion technology which has limits imposed to prevent damage to the cell electrodes.

The concepts are similar, but the approach is slightly different due to the wider voltage range.