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SolarSingle phase or three phase? The sixty-second check that decides your system size
One detail at your fuse board sets the ceiling on how much solar you can connect without asking permission first. Most UK homes are single phase, but it is worth thirty seconds to check rather than assume.
Updated 4 August 2026 · written by the Clearline guidance team
What it changes, in one line
A single phase home can fit a 3.68kW inverter without prior approval from the network operator. A three phase home can fit up to 11.04kW under exactly the same connect-and-notify rule. That is three times the capacity, available without an application, a wait or a decision from anyone.
11.04kW versus 3.68kW, same paperwork
The connect-and-notify threshold is 3.68kW per phase. On single phase that is 3.68kW total. On three phase it is 3.68kW multiplied by three, which is 11.04kW. If you have three phase and nobody has mentioned it, your quote may be sized for a limit that does not apply to you.
How to tell which you have
Look at your service head, the sealed unit where the supply cable enters the property and meets your meter. It is usually near the meter, often in a cupboard, under the stairs or in the garage.
- Single phase: one cut-out fuse and two wires, a live and a neutral.
- Three phase: three 100A fuses and four wires, three lives and one neutral.
- The meter tells you too: markings of L1, L2 and L3 indicate a three phase supply.
Look, do not touch
The service head is sealed and belongs to your network operator. Counting fuses and reading the meter markings is all you need, and all you should do. Never open, unseal or interfere with it.
Most UK homes are single phase. Three phase is more common in larger properties, converted buildings, homes with substantial electric heating, workshops or annexes, and anywhere a previous owner had a supply upgraded for a specific load.
Why the threshold exists at all
Your Distribution Network Operator owns the cables and substations that bring electricity to your street, and it has to manage what gets pushed back into them. Under G98, generation of 3.68kW per phase or less, which is 16A per phase, can be installed first and notified afterwards. Above that, G99 applies and approval must come before installation.
The threshold is applied per phase, which is the whole reason three phase homes get more headroom. Our G98 versus G99 guide covers both processes and the timescales, and what a DNO is explains who is actually making the decision.
| Single phase | Three phase | |
|---|---|---|
| Service head | One cut-out fuse, two wires | Three 100A fuses, four wires |
| Meter markings | No phase labels | L1, L2, L3 |
| Connect and notify limit | 3.68kW inverter | 11.04kW inverter |
| Above that limit | G99 application before installation | G99 application before installation |
| How common in UK homes | The large majority | Less common, more likely in larger properties |
Supply identification per UK Power Networks guidance; connection limits per UK G98 and G99 threshold guidance, accessed August 2026.
What it does not change
Panel capacity is not what the threshold regulates. The limit governs the inverter's AC rating, not how many kWp of panels sit on the roof, so a single phase home can still carry well over 4kWp of panels on a 3.68kW inverter and stay firmly within G98. Our inverter sizing guide explains why that is standard practice rather than a workaround.
It also does not stop a single phase home going bigger. It simply means a G99 application, which takes roughly four to eight weeks for a standard determination, with fast-track routes around two weeks and complex cases stretching to twelve. That is a timeline to plan around, not a barrier.
When upgrading to three phase is worth considering
If you are running a heat pump, an EV charger and a large solar array in the same property, three phase can make the whole electrical picture easier. It is a network operator job with its own cost and timescale, and it is rarely worth doing for solar alone. It is much more often worth doing when several large loads are arriving together.
If that is your situation, look at the whole electrification plan rather than the solar in isolation. Our EV charging guide and heat pump guide cover what each adds to the load, and the free design call can look at all of it together.
Send a photo of your service head and meter to a free design call, and we will tell you which supply you have and what it means for your system size.
Get your free quote →The check, step by step
Find the service head
It is the sealed unit where the supply cable enters and meets your meter. Cupboard, hallway, garage or an external meter box are the usual spots.
Count the fuses
One large cut-out fuse means single phase. Three 100A fuses side by side mean three phase.
Count the wires
Two wires, a live and a neutral, is single phase. Four wires, three lives and one neutral, is three phase.
Check the meter
Markings of L1, L2 and L3 confirm three phase. If you cannot see the service head clearly, this is the easier check.
Photograph it
A clear photo is all an installation team needs to confirm, and it saves a wasted survey visit.
Every county page on this site carries a calculator for that area so you can model a system before anyone visits. Start at your county page, or read the full solar panels guide. Installations are carried out by an MCS-certified installation team for your area, and they handle the connection paperwork with your network operator from start to finish.
Phases and supply, answered
How do I know if my house is three phase?
Look at the service head where the supply cable meets your meter. Three 100A fuses and four wires indicate three phase; one cut-out fuse and two wires indicate single phase. Your meter is a quicker check if the service head is boxed in, because L1, L2 and L3 markings confirm a three phase supply.
How much solar can I fit on a single phase supply?
Up to a 3.68kW inverter under the connect-and-notify process, with no prior approval needed from your network operator. Above that an application is required before installation. The limit applies to the inverter's AC rating rather than the panel capacity, so you can fit well over 4kWp of panels within it.
How much solar can a three phase home fit?
Up to 11.04kW of inverter capacity under the same connect-and-notify rule, because the 3.68kW threshold applies per phase and three phase homes have three of them. Beyond that a G99 application is needed. This is why three phase properties are often quoted much larger arrays.
Can I upgrade from single phase to three phase?
It is a network operator job with its own cost and lead time, and it is rarely worth doing for solar alone. It becomes a more serious consideration when a heat pump, an EV charger and a large array are all arriving at the same property. Look at the whole electrification plan before deciding.
Does three phase mean my solar will generate more?
No. Generation depends on the panels, the roof and the weather. What three phase changes is how much inverter capacity you can connect without applying for permission first, which in turn can allow a larger system on a large roof.
Do I need to check this myself before getting a quote?
It helps, because it stops a system being sized against a limit that does not apply to you. A photo of your service head or meter is enough for an installation team to confirm. Never open or unseal the service head itself, since it belongs to your network operator.
See the numbers next: LONGi 530 W panels, installed, or the solar panels guide.
Figures and specifications in this guide are sourced below and were checked on the date shown. Rates and product specifications change; we confirm the current picture on your free design call.
Sources
- Difference between a single phase and three phase electricity supply, service head and meter identification ukpowernetworks.co.uk
- Single phase and three phase power in the UK, wiring and fuse configuration uk.jackery.com
- Connect and notify limits: 3.68kW single phase, 11.04kW three phase blog.spiritenergy.co.uk
- G98 applies at 3.68kW per phase or less, which is 16A per phase sunsave.energy
- G99 determination timescales: roughly four to eight weeks standard, around two weeks fast-track, up to twelve weeks for complex cases sunsave.energy
- The threshold governs inverter AC rating, not panel kWp sunsave.energy
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