What's the difference between a single-phase inverter with a 3-CT meter and a true 3-phase inverter?

A single-phase inverter with a 3-phase energy meter sees all three phases and balances total household import to zero — but it can only inject power onto its one phase. So all its export is concentrated on L1, which causes phase imbalance and bumps into the G98 16 A limit at modest output (~3.68 kW). A true 3-phase inverter can inject independently on each phase, so output is balanced across L1+L2+L3. The 3-phase inverter is the default-correct choice on a 3-phase supply.

Does the UK smart meter net all 3 phases together for SEG export?

Yes. UK SMETS2 polyphase smart meters measure each phase separately, then sum the three algebraically before reporting an import register and an export register to your supplier. The export register only accrues when the whole-house net across all three phases is exporting. This is what makes topology 2 (three independent single-phase inverters) inefficient — they create cross-phase flows that the meter cancels out, wasting battery cycles for no SEG credit.

How do I tell if my installer fitted the wrong topology?

Run a known load on a phase that's not your inverter's phase — for example, plug a 2 kW heater into a socket on a different phase circuit. If your inverter monitoring shows no response and your smart-meter in-home-display jumps by +2 kW import while the inverter still claims self-consumption, you have a single-phase inverter on a 3-phase supply with one CT clamp (topology 1). A remote diagnostic from us pulls 7–14 days of monitoring and catches the pattern automatically.

What's the G98 vs G99 threshold for 3-phase inverters?

G98 covers installations up to 16 A per phase. On a 3-phase supply with balanced output, that's roughly 11 kW total (3 × 16 A × 230 V). Single-phase units on one phase of a 3-phase supply are G98-eligible up to about 3.68 kW (16 A × 230 V). Anything above the limit, or any install that breaks the per-phase imbalance rules, needs a G99 application to your DNO before commissioning — typically 8–12 weeks turnaround.

Guide · CT Clamps · 3-Phase Supply

CT clamps for single-phase vs 3-phase systems why installers get this wrong on 3-phase supplies

Q: Will a single-phase solar inverter work on a 3-phase house?

It will operate, but it will only generate and self-consume on the one phase it's wired to. Loads on the other two phases are invisible to it. On a typical UK 3-phase home with mixed loads, self-consumption drops to 20–45% instead of 75–88%. The inverter also breaches the G98 16 A per-phase imbalance limit if it exceeds 3.68 kW on its host phase, which means it needs a G99 application that DNOs increasingly refuse on 3-phase services.

Q: Can I just add more single-phase inverters to balance my 3-phase house?

You can, but it usually doesn't deliver what you'd hope. Three independent single-phase inverters chase their own phase to zero, but the smart meter nets all three. So when phase A exports while phase B imports, the meter cancels them out — no SEG credit, and the phase-A battery just discharged for nothing. Typical self-consumption: 55–70%, vs 75–88% for a single 3-phase inverter, at higher hardware cost.

Q: How much does it cost to diagnose a wrong-spec 3-phase inverter?

A remote diagnostic from Solar Tech Support is free, no fix no fee. We pull 7–14 days of your inverter monitoring data and cross-reference it with smart-meter readings to confirm whether the topology is wrong, what is installed, and what would need to change. If the data shows no diagnosable issue, you don't pay.

A single-phase inverter only has one CT clamp — so on a 3-phase house it can't see what's happening on the other two phases. The battery sits idle while the kitchen on a different phase runs flat out. This guide explains the four common topologies, why the UK smart meter changes the maths, and which one is the right answer.

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Written by solar engineers
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Wrong-spec inverter on your 3-phase supply?

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Prompt and useful support regarding my Sunsynk system lack of performance. Ronald simplified the technical issues to make them understandable. Many thanks, looking forward to follow up.

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Ron responded very promptly regarding my GivEnergy battery issue, his knowledgeable diagnosis was spot on and resolved the issue on first attempt. Would recommend to any and all.

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Ron made more sense in 20 mins than our installer has done over the last 12 months There is a jungle out there and you need someone like Ron to give a comprehensive overview and solution

David · May 2026

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

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I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration. So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

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This company are a rare gem, I had a very unusual problem following a failed firmware upgrade on my GivEnergy kit. I then found out GivEnergy were in administration and had dismissed all their support staff! None of the usual fixes to try and restore my inverter comms would work, and I looked everywhere, forums, GivEnergy youtube support videos - even AI couldn't figure it out. My installer was talking about huge sums for system replacements, and being vague / evasive about if they'd even install replacement GivEnergy inverter. Enter Solar Tech Support, reassuring and knowledgeable from the very start, I've learnt loads about my solar system though the friendly chat while my engineer worked as he diagnosed the problem and figured out a fix procedure that I've not found anywhere else - amazing. If you need solar system repairs - especially if you like me have been left high and dry by GivEnergy, I cannot recommend this company enough. Give them a call.

Andy Thomas · Apr 2026

I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!

Philip · Apr 2026

Very very helpfuland so quick. Made sure that a non expert like myself understood what the problem was and how to resolve it.

Declan S · Jun 2026

Mr P · Jun 2026

Sarma Amirapu · May 2026

Excellent response to diagnose a problem on our SolarEdge installation. Kept us informed at every step. Diagnosis quickly completed and solution implemented.

Les Bennett · May 2026

Prompt and useful support regarding my Sunsynk system lack of performance. Ronald simplified the technical issues to make them understandable. Many thanks, looking forward to follow up.

Patrick Keenan · May 2026

Amazing support, went out of his way to help try and get us back up and running

Paul Smith · May 2026

Andrew Palmer · May 2026

David Harris · May 2026

Ron responded very promptly regarding my GivEnergy battery issue, his knowledgeable diagnosis was spot on and resolved the issue on first attempt. Would recommend to any and all.

Simon Hill · May 2026

Ron made more sense in 20 mins than our installer has done over the last 12 months There is a jungle out there and you need someone like Ron to give a comprehensive overview and solution

David · May 2026

Ian · May 2026

Sree · May 2026

Dennis Brown · May 2026

Tony Deacon · May 2026

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026

Mr Machin · May 2026

Keith Ballard · Apr 2026

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026

Christopher · Apr 2026

customer · Apr 2026

Andy Thomas · Apr 2026

Philip · Apr 2026

Background

What a CT clamp does — in one sentence

A CT clamp (current transformer) wraps around a live cable and measures the current flowing through it without breaking the circuit. Your inverter uses its CT data to decide when to charge the battery, when to discharge, and when to push power back to the grid. If the CT misses load, the inverter misses load. Misplace a CT, install the wrong topology for the supply, and the system makes the wrong decisions — every second of every day.

On a single-phase supply the choice is simple: one phase, one CT, one inverter. On a 3-phase supply (most large UK homes, almost all commercial property, and any property with an 11 kW or 22 kW EV charger) the picture splits into four common topologies. Three of them have failure modes that show up only after install, when the homeowner notices the battery emptying while the kitchen on a different phase is running flat out.

The pivotal fact

What your smart meter actually does

UK SMETS2 polyphase smart meters measure import and export per phase, then sum the three phases algebraically before reporting an import register and an export register to your supplier. The export register only ticks up when the whole-house net across all three phases is exporting at that instant. The import register only ticks up when the whole-house net is importing.

Example

L1 exports 2 kW. L2 imports 1 kW. L3 imports 0.5 kW. Net = +0.5 kW export → SEG register accrues 0.5 kW. Now flip it: L1 exports 2 kW, L2 + L3 import 3 kW total. Net = −1 kW import → import register accrues 1 kW. The export register doesn't move. One inverter cannot tell what's happening on the other two phases unless its CT setup measures all three.

This is the single most important fact in this guide. Everything below — why topology 1 fails, why topology 2 wastes battery cycles for no SEG credit, why topology 3 works but stresses one phase — derives from how the smart meter sums.

Topology 1

Single-phase inverter on a 3-phase supply (one CT on L1)

The most common wrong-spec install. The inverter only knows what's happening on the phase it's wired to.

Generation / export

Grid import (paying)

Mixed / partial import

CT measurement point

The inverter is wired to L1, neutral, and earth. Its single CT clamps around the L1 incomer at the consumer unit. The inverter sees L1 only — it has no visibility of L2 or L3, no awareness of cross-phase loads, and no ability to inject or absorb current anywhere except L1.

When L2 has the kettle on (3 kW) and L1 is idle, the inverter sits there with a full battery while the meter charges you for 3 kW. When L3 is charging an EV at 7 kW, you import the full 7 kW from the grid — the battery doesn't fire because the inverter doesn't see the load. When L1 has its own load, the inverter does what it's designed to do, but only on a third of the household.

Typical self-consumption on a UK 3-phase domestic supply with this topology is 20–45% of generated kWh, against 75–88% achievable with topology 4. There is no software fix. The fix is to change inverters.

It can also breach DNO rules. A single-phase 5 kW inverter on one phase is 22 A on that phase — above the G98 16-amp-per-phase limit, so the install needs a G99 application that's rarely granted on a 3-phase supply where a balanced product exists. The over-export onto one phase also raises L1 voltage and triggers the inverter's own G99 over-voltage trip sooner than a balanced install would.

Topology 2

Three single-phase inverters, one per phase (three CTs)

Looks balanced on paper, fails on UK net metering.

Generation / export

Grid import (paying)

Mixed / partial import

CT measurement point

Three single-phase inverters, each with its own DC array or battery, each wired to one phase, each with one CT measuring its own phase. The three inverters operate independently — none of them has any visibility of what the others are doing.

Each inverter tries to zero its own phase. Locally, each phase is balanced. But the smart meter is netting all three phases, and the inverters don't know it.

The failure mode is wasted cycling. L1 inverter exports 2 kW to cover its own zero-target. L2 inverter imports 2 kW from the grid because L2 has a 2 kW load and an empty battery. The meter sees: net zero. You're billed nothing for that instant — but no SEG credit either, and the L1 battery just discharged 2 kW for nothing.

Worse, the cross-phase asymmetry can shift hour to hour. SEG export only registers when the whole-house net is exporting. With three independent inverters chasing per-phase zero, the system will routinely create flows that the meter nets to a wash, paying neither party. Typical self-consumption: 55–70% — better than topology 1, worse than 3 or 4.

It's also the most expensive of the four. Three inverters + three CTs cost roughly 50–100% more than a single 3-phase unit of equivalent total kW. The only times it's the right call: heritage upgrades being done one phase at a time, or where each phase needs its own backup-power island.

Topology 3

Single-phase inverter with a 3-phase energy meter

One inverter, all output on one phase — but it sees all three phases. Works on UK SEG.

Generation / export

Grid import (paying)

Mixed / partial import

CT measurement point

Electrically the inverter is wired to one phase (typically L1). Instead of a CT clamp it uses an external 3-phase energy meter sitting on the supply tails, reading all three phases and reporting whole-house net via Modbus RS485 back to the inverter.

The inverter's control loop targets total imported power = 0 across the sum of L1+L2+L3. If L2 has 2 kW kettle and L3 has 1 kW load, the inverter pushes 3 kW out onto L1. The smart meter sees L1 = −3 kW, L2 = +2 kW, L3 = +1 kW → net 0. Exactly the behaviour SEG was designed to reward.

Self-consumption matches topology 4 in steady state — typically 70–85%. The catch is what happens when the inverter is exporting hard onto one phase.

A 5 kW inverter exporting at full tilt onto L1 = ~22 A on that phase. That exceeds the G98 16 A per-phase imbalance limit, which means the install needs a G99 application. Some DNOs accept this on weak networks; others won't. Below ~3.68 kW it's G98-eligible. Above it, you're applying to the DNO and they may refuse if the local LV network can't tolerate the imbalance.

It's the right answer when a 3-phase inverter isn't available in the desired battery ecosystem, when the inverter capacity stays under 16 A on one phase, and when the DNO accepts the imbalance current. It's the wrong answer when you need more than ~3.68 kW of continuous output and the DNO won't grant G99.

Topology 4

True 3-phase inverter (three CTs or a 3-phase meter)

The default-correct topology. Each phase metered, each phase balanced.

Generation / export

Grid import (paying)

Mixed / partial import

CT measurement point

The inverter has three independent phase outputs (or a firmware-bonded 3-phase cluster). It can source or sink current on each phase independently. It uses either three CT clamps (one per phase) or an external 3-phase Modbus meter to measure all three phases.

Each phase is balanced to zero against its own load. If L1 has 2 kW load, the inverter supplies 2 kW on L1. If L2 has 1 kW load, it supplies 1 kW on L2. If there's surplus PV after household load, it exports balanced kW across all three phases.

Self-consumption is the highest of the four topologies — typically 75–88% of generated kWh — and the residual loss is just the standard battery-empty edge cases that affect any storage system.

Balanced by design means no P29 voltage-unbalance risk and no G98 imbalance breach. G98-eligible up to 3 × 16 A = ~11 kW total inverter output on a 3-phase service; anything above goes G99.

The premium over single-phase: typically 20–40% on inverter hardware, plus ~£150–250 for the 3-phase meter if it isn't bundled. For any 3-phase supply that's getting more than ~3 kWp of PV or a battery system intended to cover the whole house, the premium pays back inside the system lifetime through self-consumption gains alone — never mind the resilience of getting the topology right first time.

Comparison

Side-by-side comparison

Topology	CTs	G98 ceiling	SEG net works?	Self-consumption	DNO risk
1 — 1-ph inv, 1 CT	1× on L1	16 A on one phase	Partly — meter nets but inverter is blind to it	20–45%	Voltage rise on one phase; imbalance
2 — 3× 1-ph inverters	3× (one per inverter)	16 A/phase, balanced	Partly — cross-phase waste	55–70%	Multiple-G98 acceptance varies by DNO
3 — 1-ph inv + 3-ph meter	External 3-phase meter	16 A on host phase	Yes — designed for it	70–85%	Imbalance current on host phase
4 — True 3-phase inverter	3× CTs or 3-phase meter	3×16 A ≈ 11 kW total	Yes — designed for it	75–88%	None notable

DNO rules

G98 vs G99 — the rules behind the topology choice

The UK distribution code from ENA (Energy Networks Association) sets two thresholds that decide which paperwork applies:

G98 — Connect and Notify

Up to 16 A per phase. At 230 V that's ~3.68 kW single-phase or ~11 kW total on a balanced 3-phase install. You install first; the DNO is notified within 28 days. No pre-approval.

G99 — Apply and Connect

Anything above 16 A per phase, or any installation with multiple G98 units at one premises that breaks the imbalance rules. You apply to the DNO before commissioning. Turnaround is typically 8–12 weeks.

The imbalance rule is the part most installers miss. Multiple G98 single-phase units at one premises are only acceptable when the imbalance between phases does not exceed 16 A. That's why topology 3 (single-phase inverter pushing all output onto L1) bumps into G99 the moment the inverter exceeds 3.68 kW continuous — not because the inverter is over 16 A in isolation, but because the imbalance current at the consumer's installation goes over.

If you want the full picture on the paperwork, see our G98 vs G99 explained guide.

EV charging

EV chargers — the topology stress test

A 3-phase EV charger draws roughly 16 A on each of the three phases (11 kW) or 32 A on each (22 kW). For the single-phase EV-charger CT placement story, see our EV charger CT placement guide. This is where the topology choice shows up most aggressively on the homeowner's bill.

Topology 1

5 kW single-phase inverter covers ~1/3 of the EV load if it happens to share a phase. Solar self-consumption during EV charging: 0–33%.

Topology 3

Inverter pushes 5 kW onto L1 to offset 11 kW total. Meter nets to 6 kW import. Solar covers ~45% of EV load.

Topology 4

9–11 kW 3-phase inverter fully covers an 11 kW EV charge. Solar self-consumption: ~100%.

22 kW charger

No domestic inverter has the capacity. Topology 4 still minimises grid draw the most.

If you're adding an EV charger to a 3-phase house — or planning a new solar install for one — topology 4 is the only choice that makes the numbers work.

Industry context

Why most installers default to single-phase even on 3-phase supplies

It isn't usually malice — it's friction. The reasons are mundane and they stack up:

Stock and training

The van carries single-phase hybrids. They don't normally stock 3-phase units.

Cost

20–40% inverter premium, plus a 3-phase meter at £150–250, plus more complex CT routing.

Battery ecosystem

Several popular UK battery stacks were single-phase-only until recently. The installer wants the chemistry they know.

Commissioning

Single-phase + one CT can be commissioned by one electrician in half a day. 3-phase needs phase-rotation checks and balanced-output verification.

DNO paperwork

G98 single-phase notify is 28 days post-install. G99 is 8–12 weeks pre-approval. Installers under quota pressure choose the path that ships fastest.

None of these reasons survive contact with the homeowner's actual bills, but they explain why so many 3-phase supplies end up with the wrong topology in the first place.

Pre-install audit

What to ask your installer (or your existing installer)

Before commissioning, or as a post-install audit:

Is my supply single-phase or 3-phase?

If you don't know, check your meter. Three meter tails coming in (excluding neutral and earth) = 3-phase.

Is the inverter single-phase or 3-phase?

Read the model number off the inverter itself. “1P”, “1-phase”, or “single-phase” in the datasheet means it generates on one phase only — regardless of how many CTs it accepts.

How many CT clamps are fitted, and on which phases?

One CT on a 3-phase supply = topology 1, and you need to know that going in.

What does the inverter chase to zero — one phase or the whole house?

If the installer can't answer this, the chances are it's topology 1.

Was a G99 application filed?

If the inverter is over 3.68 kW on one phase and there's no G99 reference, the install may not be DNO-compliant.

DIY diagnostic

How to spot you've got the wrong topology — without opening the inverter

The fastest diagnostic without lifting a panel:

Run a known load on a phase that's not the inverter's phase — e.g. plug a 2 kW heater into a socket you know is on a different phase circuit.

Watch the inverter monitoring app. If the battery doesn't respond and the grid import jumps by 2 kW, the inverter can't see that phase. Topology 1 confirmed.

Cross-reference with the smart-meter in-home-display (IHD) reading. If the IHD reports +2 kW import while the inverter says “self-consumed”, the inverter is operating on bad data.

A remote diagnostic from us pulls 7–14 days of monitoring history and looks at the cross-phase pattern automatically — usually catches a wrong-topology install inside the first 30 minutes. For the wider “CT clamp installed wrong” symptom set (reversed readings, battery not charging, monitoring inverted), see CT clamp installed wrong.

FAQ

Frequently asked questions

Will a single-phase solar inverter work on a 3-phase house?

It will operate but only on the phase it's wired to. Loads on the other two phases are invisible to it. Typical self-consumption drops from 75–88% (with a 3-phase inverter) to 20–45%. It also bumps into the G98 16 A per-phase imbalance rule above ~3.68 kW continuous output, so over that figure it needs a G99 application.

How does my UK smart meter handle 3-phase solar export?

SMETS2 polyphase smart meters measure each phase separately, then sum them algebraically before reporting an import register and an export register to your supplier. The export register only ticks when the whole-house net across all three phases is exporting. This is why topology 2 (three single-phase inverters) wastes cycles — phase-A export gets cancelled by phase-B import at the meter, with no SEG credit either side.

What's a 3-phase energy meter and which inverter brands use them?

It's an external meter clamped around all three phase tails at the supply incomer, communicating with the inverter via Modbus RS485. The inverter uses it instead of (or in addition to) CT clamps to net total household import to zero. Common 3-phase meters in the UK channel include the Carlo Gavazzi EM24, ET340, and EM340, and similar Eastron units. Several single-phase inverter ranges support this mode for net metering across phases.

Can I use 3 single-phase inverters instead of one 3-phase inverter?

You can, but it usually performs worse than a single 3-phase inverter and costs more. Each inverter chases its own phase to zero. The smart meter nets all three. So when phase A exports while phase B imports, the meter cancels them — no SEG credit and a battery cycle wasted. Typical self-consumption: 55–70%, vs 75–88% for one true 3-phase unit.

How do I check if my topology is wrong without opening anything?

Run a known load (e.g. a 2 kW heater) on a phase that's not your inverter's phase. Watch the inverter app and your smart-meter in-home-display. If the IHD jumps +2 kW import while the inverter shows no response, it's topology 1 — single-phase inverter, one CT, blind to the other phases. A 30-minute remote diagnostic from us pulls 7–14 days of monitoring and catches the pattern automatically.

What's the right topology for a 3-phase supply with an 11 kW EV charger?

A true 3-phase inverter (topology 4), sized at 9 kW or above, ideally with a 3-phase battery system. The EV draws ~16 A on each of the three phases. Only a 3-phase inverter can offset all three. A single-phase inverter on one phase (even with a 3-phase meter) caps at ~3.68 kW and can only offset roughly a third of the EV load. The maths only works for topology 4.

How much does it cost to diagnose a wrong-spec 3-phase inverter?

A remote diagnostic from us is free, no fix no fee. We pull 7–14 days of your inverter monitoring data and cross-reference it with smart-meter readings to confirm whether the topology is wrong, what's installed, and what would need to change. If the data turns out to show no diagnosable issue, you don't pay. See the remote diagnostic service for the full scope.

How long does the diagnostic take?

Most 3-phase topology diagnoses are done inside a single 30-minute session. You book a slot, share your monitoring login (or screenshots) and your smart-meter half-hour data if you have it, and we work through the cross-phase pattern. The written engineer report — clear enough to take to your installer or your DNO — is usually returned the same day.

Think your installer fitted the wrong inverter for your 3-phase supply?

A remote diagnostic confirms the topology from monitoring data and gives you a written engineer report — clear enough to take to your installer or to a DNO. From £75, no fix no fee.

Call 07944 877 329 Book free diagnostic