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Isolating the system for a planned power cut

TRBob · 2025-08-20T13:07:09Z

There is an upcoming planned power cut, see the attached letter that I got from NPG. It will be for about 28 hours whilst they do some work to our local network and we will be put on a generator. It says to isolate generation equipment (a heat pump is an electrical generator?!?) from the mains supply, but I'm pretty sure that my inverter will do this anyway when it loses mains power. Plus my PV isolators will not physically close when under load, I can only turn them off at night. Would turning the trip off in the consumer unit be enough?

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Transparent

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14/10/2025 12:55 pm

@batpred - that Solis installation page is too vague.

Yes, they state that there's RCD protection inbuilt to the inverter.
But we don't know to what extent that offers protection to the inverter itself,
nor whether that protection covers appliances which are connected to the always-on port.

As matters stand, that integral RCD would still leave the supply cable and isolation switch unprotected.

I don't like having any conductors leaving the distribution board without both over-current and earth-leakage protection.

The regulations for new installations are even tighter.
You now need ARC-detection trips within the consumer unit.

Those will disconnect the circuit in the event of cable damage within the wall - perhaps vermin eating the insulation.
Whether that measure will reduce house-fires or not is too early to say, but insurers like it.

This post was modified 5 months ago by Transparent

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Batpred

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16/10/2025 1:49 pm

I will continue the discussion on the solis installation on the Fogstar battery thread

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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Batpred

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16/10/2025 3:44 pm

Bu the way, my understanding is that arcing detection is not required for new circuits unless it is a shared use property? Or is it only for rental properties?

As for SPD protection, for the extra £20 or so when getting a new unit, it was a no brainer. It also helped us removing the ad-hoc surge protectors we had like to stop the boiler PCB blowing up when power comes back following a black-out.

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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Transparent

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16/10/2025 4:16 pm

Posted by: @batpred

↑

my understanding is that arcing detection is not required for new circuits unless it is a shared use property?

That's correct.

I was mentioning it as something which would be a future requirement.

Both arc-detection and surge suppression devices (SPD) are like paying an insurance package.
Even if you decide not to implement them, you should at least know that they are available options and why.

There are also different levels of protection offered, according to the specification of the devices you choose to install.

Your SPD might do all that you want at £20.

On the other hand, I use high-end Phoenix Contact suppression systems on both mains and PV panel connections.
The pair in the consumer unit which receives the mains incomer cost substantially more than £100.

There are reasons why some insurance premiums cost less than others.

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Batpred

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16/10/2025 5:04 pm

Insurance helps and when adding high powered devices like EV chargers, PV panels and some inverters and heatpumps, the other circuits may need to be a bit more shielded, and future proofing is also worth. We had our supply upgraded to 100A but only after a few years and another visit did I feel they had given us that insurance.

Price of components can also be driven by volume and other considerations like supply chain requirements to recoup r&d costs.

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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Transparent

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17/10/2025 9:39 am

Apologies, I don't follow what you've written @batpred

The possibility of damage from surges doesn't increase with 'high powered' devices.

In fact the device most likely to be damaged by a surge or spike on the mains is a landline telephone or internet router, supplied by copper wires.
That's because there can be a voltage difference between the mains and the telecom cables.

Posted by: @batpred

↑

We had our supply upgraded to 100A but only after a few years and another visit did I feel they had given us that insurance.

I was referring to 'insurance' as a metaphor.

The size of the service fuse doesn't change the susceptibility to damage from surges.

Posted by: @batpred

↑

Price of components can also be driven by volume and other considerations like supply chain requirements to recoup r&d costs

Phoenix Contact surge arresters dominate the commercial market.
There are thousands of types in their catalogues.

They are proven to be affective because Pheonix Contact are based in the Black Forest, in the south of Germany.
That area has the highest number of lightning storms in Europe.
They can easily test products in real-world conditions as well as a laboratory.

It's relatively easy to make a surge arrester which protects equipment from a single spike.
The key point is what then happens to the arrester?
If it doesn't recover to full operational specification, then it's useless.
The next surge will get through.

Buyers are prepared to pay more for an anti-surge device that is more likely to provide protection.

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Batpred

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17/10/2025 11:49 am

@transparent 😊

I may have lost you there.. I use the insurance term as proxy for the "additional life" that was only given when the DNO replaced some components that despite being rated for 100A, were more fitting as museum pieces!

When I broadly mentioned circuits needing to be "shielded", it was not in the electrical sense, a better word may have been "cushioned". Specifically that when inverters and similar components are added to a household, some components that protect other circuits like RCDs type AC need replacing, ideally with RCBOs type A. We had a mid sized plastic consumer unit and that went a few months ago, as part of the prep.

8kW Solis S6-EH1P8K-L-PLUS hybrid inverter; G99: 8kw export; 16kWh Seplos Fogstar battery; Ohme Home Pro EV charger; 100Amp head, HA lab on mini PC

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