Solar Inverter Tripping on High Grid Voltage?

Why your inverter trips at 253V (and what the limits really are)

UK nominal voltage is 230V. Under the Electricity Safety, Quality and Continuity Regulations 2002, your network operator (the DNO) must keep the supply at your cutout between 216.2V and 253V, which is 230V minus 6% and plus 10%. That upper figure is the one everyone quotes.

Your inverter has its own rules, set by the G98 and G99 connection standards, and two protection stages matter here. The slow one trips the inverter when the average voltage at its AC terminals stays above 253V for ten minutes. The fast ones act on spikes: typically about 262V within a second, and about 274V within half a second. Most midday trips are the slow, ten-minute kind. The standards exist because pushing export current into a network that is already near its legal ceiling would lift voltages for your neighbours’ fridges, tellies and EV chargers.

So how does it get up there? Push current down any cable and the voltage at the far end rises in proportion to the cable’s resistance. When you export, the voltage at your inverter sits above the voltage at your meter by however much your own wiring adds. Underneath that sit the transformer’s tap setting, the length of cable from the street to your house and whatever the rest of the road is exporting at the same time. On a sunny weekday, with everyone out and no kettles on, those rises add up fast.

That’s also why a perfectly legal supply can still trip your inverter. A reading of 250V at the cutout is inside the limit, but it leaves just 3V before the inverter reaches 253V. The extra volts come from three places, and it matters which one is yours:

What over-voltage tripping looks like in your logs

Over-voltage has a signature. Trips cluster between roughly 11am and 3pm on clear days, and they’re worst in late spring and summer, when panels are happy and street demand is low. Cloud rolls over and the fault clears. Winter barely triggers it. If your cut-outs happen at 7am or in the rain, you’re hunting something else: our inverter fault codes explained guide covers the damp-morning and earth-fault families.

There’s also a quiet version. Some inverters throttle their output as voltage creeps towards the limit, so you get a flat-topped generation curve on sunny days with no fault code at all. If your app shows a ceiling well below what your array should make at midday, check the AC voltage trace before you blame the panels.

After a trip the inverter waits at least 20 seconds, then runs its own checks, so it normally restarts within one to five minutes. If that cycle repeats every few minutes, voltage is still sitting on the limit. Our piece on the G98/G99 reconnection wait explains the timing.

What the screen says varies by maker and firmware. Roughly:

Wording shifts with firmware, so your manual has the final word. The message matters less than the voltage behind it. Fronius, plus the earth-fault and arc codes, are in the full table in our brand-by-brand fault code translator.

Before anything else, pull the logged AC voltage at the moment of the trip. That single figure is most of your diagnosis. If your monitoring is thin or missing, fix that first: a decent solar monitoring setup pays for itself the first time something like this goes wrong. And if the trips have left you with no generation at all, check why your panels are producing nothing before assuming voltage is the culprit.

Five checks before you call anyone

1. Check the pattern. Clear-sky middays only? That points to voltage. Random times in any weather? Look elsewhere.
2. Compare lunchtime with 6pm. Read the live AC voltage on the inverter display (or in the app) at both times. A swing of 8 to 10V tells you voltage is moving with sunshine and street demand, which fits an export problem. The next section shows how to split your share from the network’s.
3. Look at the AC isolator and the inverter casing. Scorch marks, buzzing or a smell of hot plastic mean a bad joint adding volts and fire risk. Switch the AC isolator off if it’s safe to reach, and get someone out that week, not next month.
4. Ask the street. A neighbour with solar who trips in the same window points to the network, which changes who pays.
5. Think about what changed. A new battery, heat pump, array extension or DNO works nearby all shift the voltage picture, and faults that start the week after a change are rarely coincidence.

Your wiring or their network? Read the headroom

Here’s the test I’d ask any installer to run, and the one I’d want to see written down. Log the voltage in two places across a sunny midday: at the main intake or consumer unit, and at the inverter’s AC terminals. Do it twice, once with the solar isolated and once with it exporting. Householders can’t do this safely, so ask your installer or a qualified electrician with a logger. What you’re after is your headroom: 253V minus the voltage at the intake with your solar off.

The 246V line is a rule of thumb, not a standard: it’s 253V less about 2.3V for your own wiring and a few volts for the extra rise your export causes upstream. DNOs tend to judge complaints on sustained readings, often 10-minute averages, rather than single spikes, so a clean week-long log carries more weight than one screenshot.

Branch C is the one nobody warns you about. The DNO isn’t breaking any rule at 250V, so it isn’t obliged to change anything, yet your inverter still trips. That’s when your own wiring and export settings have to carry the fix.

The fixes, ranked by cost and faff

Ranges follow our repair-cost guide, where a call-out alone runs £80–£150. They include labour but not scaffolding, which cable runs to the consumer unit rarely need. Repairs normally carry 20% VAT, whereas a battery installation is zero-rated in Great Britain until 31 March 2027. Get three quotes, and see what solar repairs actually cost in 2026 for the wider picture. Like-for-like replacement of a damaged cable run is cheaper than upsizing a long one.

Cable and connections first

Always. It’s the cheapest cure when your wiring is the problem, it’s quick, and sometimes it also removes a fire risk nobody had noticed. If an installer quotes you a new inverter before measuring the voltage rise across your AC cable, thank them for their time and ring someone else.

Export limits, diverters and batteries: know the price of quiet

An export cap stops tripping because less exported current means less voltage rise. Your installer sets it in the inverter, it works straight away and costs almost nothing. The catch is that it quietly gives away some of your generation.

Rough worked example: a 4kWp array peaks at around 3kW in a UK summer. Cap export at 2.5kW and you lose roughly 0.5kW at the peak, which adds up to perhaps 1.5 to 3kWh on a clear day. At 7p/kWh, the SEG rate we use in our savings estimates, that’s about 10p to 20p a day, or £10 to £20 over a summer. At a 15p tariff the loss roughly doubles. Check what you’d really lose with our SEG income estimator and the SEG rate comparison. For a fault-free system that’s often the right trade, as long as you make it deliberately.

A battery does the same job more elegantly: it soaks up the midday surplus and hands it back at teatime, so the voltage problem becomes a saving. But a battery bought purely as a voltage fix is an expensive remedy for what is often a few-hundred-pound wiring fault. If you were already weighing one up, this tips the scales, and the 0% VAT window closes on 31 March 2027 (it’s 5% after that, and Northern Ireland follows different VAT rules). Our guide to adding a battery to existing panels covers the retrofit maths.

If hot water is your big daytime load, a diverter does a similar job for less. It sends the surplus to your immersion heater instead of the grid, which also trims midday export. Diverter vs battery helps you decide which to buy first.

What never works

Buying a “wide voltage range” inverter. The protection limits are part of the G98 and G99 type testing, so you can’t simply fit a UK-compliant unit with a higher ceiling. Anyone offering to “adjust the limits” in the installer menu on a whim is offering to breach your connection agreement, and cowboy changes can void your warranty and your MCS paperwork. Where the DNO has measured the voltage and agreed different settings, an installer can apply them through the proper channel. That’s the only legitimate route.

Be wary of “voltage optimiser” sales pitches too, especially ones built around a reading like 244V, which is well inside the legal range. They aren’t a recognised remedy for export over-voltage under G98 or G99, so get your DNO’s or an MCS installer’s view before paying anyone. Our list of solar panel scam red flags shows what the pitch usually looks like. And if the inverter really is at the end of its life for other reasons, that’s a separate conversation: see inverter replacement in the UK.

When the DNO owes you a fix

If branch A is your answer, with the intake sitting above 253V even though your solar is off, the network is out of spec and the fix is the DNO’s cost, not yours. Usually it’s a transformer tap change: a van and a setting, no digging. Occasionally it’s local reinforcement, which is slower.

Not sure who your DNO is? Call 105, which is free and open 24 hours, and it puts you through to your network operator (in Northern Ireland the number is 03457 643 643). Then put the problem in writing to the DNO’s voltage or power quality team, with an evidence pack:

• Dates and times of every trip, with screenshots of the AC voltage trace from your app.
• Your inverter’s fault log and the exact message it shows.
• Any intake voltage your installer logged, ideally with the solar switched off.
• Your installer’s name and your connection paperwork (the G98 notification or G99 approval).

Ask specifically for a voltage logger to be fitted at your cutout for a week or so, and for a tap review if it confirms sustained readings above 253V. If the DNO replies that everything is within limits, ask for its measured data. Readings that sit just under 253V while your inverter still trips put you in branch C, where the answer is a mix of tidying your own wiring and capping export. If the DNO sits on a confirmed problem, use its formal complaints process, then the Energy Ombudsman, which is free for householders.

While you wait, an export cap keeps the system earning something instead of nothing. Just remember to relax or remove it once the network is fixed, or you’ll keep paying for a problem that no longer exists.

Catching this before install, not after

Wiring-side over-voltage is the most preventable version of this problem. If you’re buying solar now, ask for these in writing before you sign:

• The voltage-rise calculation for the cable between the inverter and the consumer unit, sized for about 1% rise rather than just for current.
• The inverter sited as close to the consumer unit as practical.
• A look at your street’s voltage around a sunny midday before the quote is finalised, if the installer is willing to log it.
• An honest conversation about export on a solar-heavy street, where a battery or diverter planned in from the start beats an export cap bolted on later.

An MCS-certified installer treats this paperwork as routine. How to choose a solar installer covers the questions that smoke out the cowboys, and our explainer on what the MCS badge means shows what it does and doesn’t guarantee.

If your system is merely shy rather than tripping, with low yields and no fault codes, that’s a different hunt. Start with solar panels underperforming.

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