Since the phase change, the situation has improved dramatically. 

Slightly odd to note 3 days 3,4,5 July with multiple overvoltage events. However afaik there may have been no inverter disconnects - we normally hear the relays. And solar prod did not appear impacted. So perhaps brief spikes for some reason.

The last 5 days have seen no events and voltage in a better range despite high solar etc. Of course its possible DNO have done something that I am unaware of.

I will continue monitoring for now 

With the Powerwall 2 or 3 with a Gateway, grid voltage and frequency monitoring, and Grid disconnection is outwith the end user’s control.

And that's as it should be.

If the grid parameters could be adjusted after manufacture, then it shouldn't get G98 certification.

I remain concerned, however, that some manufacturers might retain a back-door through which they can upgrade the firmware and configuration remotely.
That's a downside of having inverters which can only be operated if the customer connects them to the manufacturer's site across the internet.

Personally I think it should be made illegal to have mandatory internet communications in order to use an inverter.
It would still be possible to use Bluetooth or a secure WiFi connection to communicate directly with an App on a Smart-Phone.

@tim441  - please don't send anything to me.

SSE must have direct communication with their customers for GDPR reasons.

Once the file notes have been looked at internally, they will decide the next step.

My role is to liaise with senior engineers in a DNO, to discuss the issues and risks which come to light here on the Forum. I'd like to see a generic appreciation of the problem, and a collaborative approach to deal with it.

The benefit of this Forum is that one member raises a problem, and then three others join in with "me too".
That allows a DNO to better evaluate the nature of the issue, and clarify whether it's a few faulty devices, or a generic problem which is going to grow if nothing's done.

I don't know if that would be useful if sent to you by email? Could you forward?

Definitely my overvoltage events and inverter disconnects havd massively reduced since the phase change. But as you point out... the underlying problem is not resolved

The same logic applies to EVs and EVSEs. They will also respond to under/over-voltage situations by disconnecting from the Grid.

If there ever is an under-voltage situation, the PW3 plus Gateway 2 will take my home off the grid.

May I persuade you to see the effects of this from the viewpoint of the grid...

When an inverter disconnects itself from the grid, any export which it might have contributed is no longer available.
Consequently the voltage falls further.

That gets detected by another few inverters on the same local substation...
... which also disconnect under their G98 certification.

This happens rapidly because they are electronic devices.

The grid still has to meet the demand for those properties, and the additional call for power on the 11kV supply causes its voltage to fall.

And we can all see where this is heading!

The quotation is taken from the Factual Report on the Iberian Outage of 28th April 2025.

Small-scale embedded generation suffered a Cascade Effect, requiring the Spanish Grid to make up a sudden shortfall of power.

Historically the grid would've remained in full operation because of the inertia provided by generators using rotating turbines.

But when these are progressively being replaced by electricity from renewable sources, it leaves the grid more susceptible to an outage.

Once we start enjoying the financial benefits of exporting to the grid, we assume the social responsibility to continue doing so.
That's what should occur with a correct implementation of G98.
But we're now beginning to see chinks in that armour.

God, grant me the serenity to accept the things I cannot change, the courage to change the things I can, and the wisdom to know the difference."

The DNO was happy that the matter could be resolved by tapping the upstream pole-mounted transformer. The DNO set a notional 240VAC to avoid any low-voltage problems further downstream in a rural area.

And what will happen when the ENA approves a nationwide voltage reduction by reducing the 11kV output from all Primary substations?

Your DNO won't know whether they need to return to your PMT (pole-mounted transformer) and change the tap back again.
There's no monitoring on the vast majority of LV supplies or local substations.

The DNO is 'blind' to what happens at the far ends of rural routes.

Instead of just attending on-site to look at a case of under/over-voltage, it's important to locate the equipment which isn't compliant.

My high voltage ‘fault’ had nothing whatsoever to do with my solar inverter or Powerwall 3. My Powerwall 3 took the Grid offline at night with a voltage of 256VAC.

The DNO was happy that the matter could be resolved by tapping the upstream pole-mounted transformer. The DNO set a notional 240VAC to avoid any low-voltage problems further downstream in a rural area.

Luckily my DNO was helpful & proactive. Switch of phases has very significantly improved the situation. But there is probably still an issue on my local grid at another property that is causing overvoltage. I don't know if the DNO will track it down - or have bigger fish to fry!

Tim - your DNO is back on the case.

I spent 20mins yesterday in conversation with a senior SSE Engineer.

A local DNO manager told me that 75% of his time is now spent on resolving under/overvoltage situations.

That shouldn't be happening, of course.

No G98/G99 certified device should be capable of taking the grid above 253v.

In Tim's case there is reasonable evidence that there is an inverter nearby which is doing just that...
... and in a sustained way, which causers other G98 devices to disconnect from the grid.

We need to find that device!

Let's suppose it turns out to be a commonly-installed solar-inverter which is manufactured in the Far East.
Then let's imagine that it requires home-owners to allow remote monitoring across the internet so that data can be accessed via their mobile phone...

... but that the Manufacturer has used those internet connections to remotely apply a firmware upgrade which hasn't been checked for G98 compliancy.

Until we find what that type/model of inverter is, the problem will continue to be replicated across Britain.

Other legally-certified inverters of all sorts will be taken out of action every time one of those rogue inverters disobeys the rules.

That leaves us more susceptible to a Cascade Effect, in which embedded generation fails across a wide area.

Ignoring what is being posted here on this topic is not an option.

@l8again - it sounds like your DNO needs to be more pro-active. Who are they?
Instead of just attending on-site to look at a case of under/over-voltage, it's important to locate the equipment which isn't compliant.

... and that's before we start adding "Plug-In Solar" kits to the equation!