How to Convert a Single-Phase System to Three-Phase Using Victron MultiPlus-II in the UK

Upgrading from a single-phase to a three-phase power system is becoming increasingly popular across the UK, particularly for homeowners and businesses looking for greater flexibility, energy independence and compatibility with high-powered equipment. In this guide, we’ll explain how we upgraded our business from single-phase to three-phase and how you can do the same using Victron MultiPlus-II inverters, one of the world's most trusted solutions from Victron Energy UK.

Why Convert from Single-Phase to Three-Phase?

Most UK households are supplied with single-phase (230V) electricity. However, certain appliances, such as heat pumps, electric vehicle chargers, and industrial equipment, require a three-phase (400V) connection. A three-phase system also offers improved load balancing, reduced current draw per phase and enhanced performance for large or critical systems.

While upgrading the grid connection to three-phase is often costly and complicated, you can create a genuine full three-phase system using inverters, an increasingly practical solution with products like the Victron MultiPlus-II 3 phase inverter setup we've done here.

What is the Victron MultiPlus-II?

The Victron MultiPlus-II is a hybrid inverter/charger designed for both off-grid and grid-connected applications. It supports energy storage, solar charging, generator input and smart grid interaction. When used in combination, multiple MultiPlus-II units can be programmed to form a 3-phase inverter system, offering full compatibility with three-phase loads. For our system we are using 3 x Victron 8kVA Inverter/Chargers.

How to Set Up a Victron MultiPlus-II Three-Phase System

To create a three-phase inverter system in the UK using Victron MultiPlus-II, you'll need at least the following:

• Three Victron MultiPlus-II inverters, each representing one phase (L1, L2, L3) 

• Battery bank (such as Pytes ESS Lithium Batteries )

• Victron Cerbo GX or Venus GX for system monitoring and control

• MK3-USB interface to configure the system

• VE.Bus communication cables for synchronisation

• Optional MPPT solar charge controller (e.g. Victron MPPT RS 450/100)

Configuration Process:

The configuration process involves mounting and wiring the MultiPlus-II unit independently ensuring each one is assigned their own phase and that the battery bank is connected and set up evenly so all the inverters draw from the same battery system.

Adding a Cerbo GX 2 and a Touch 50 screen allows you to configure, monitor performance, battery levels, grid input and solar input.

On our system we've got an Victron MPPT RS 450 | 100 so we can connect solar up to the same battery system to recharge the batteries.

Key Benefits of Using Victron MultiPlus-II in the UK

• No need for a DNO upgrade: Avoid the cost and complexity of upgrading to a three-phase supply from your network operator.

• Reliable power backup: Maintain power during grid outages using stored battery energy.

• Smart energy control: Optimise solar generation, battery storage and grid usage using Victron’s VRM Portal.

• Modular: Victron systems are modular and can be expanded or modified to suit your needs.

• Compliant with UK regulations: The MultiPlus-II is G98 and G99 compliant, supporting grid-tied configurations legally in the UK.

Real-World Use Cases

• Rural properties using solar and battery storage where the grid is unreliable or expensive to upgrade

• Workshops or small businesses that need three-phase machinery but are located in single-phase areas

• Electric Vehicle owners requiring fast charging systems typically only supported by three-phase supply

• Homeowners looking to balance large domestic loads, especially in properties with heat pumps, underfloor heating and other systems with high draw.

Monitoring and Remote Management

All Victron systems can be accessed remotely via the Victron Remote Management (VRM) platform. This cloud-based portal offers real-time monitoring, remote firmware updates, and historical data logging. The Cerbo GX device, often mounted with a touchscreen display, acts as the heart of your monitoring system.

Final Thoughts

Converting from single-phase to three-phase using the Victron MultiPlus-II 3 phase setup is a powerful solution for energy conscious users in the UK. It provides flexibility, backup power and compatibility with modern electrical demands, without relying on the national grid for a costly upgrade.

Whether you are an installer, homeowner or business owner, this approach delivers a smart, modular, and future-proof system tailored to UK requirements.

Frequently Asked Questions

Is a Victron MultiPlus-II system G99 compliant in the UK?

Yes, most models are fully compliant with G99 regulations, making them suitable for grid-tied installations in the UK.

Can I add solar panels to a Victron 3-phase inverter setup?

Absolutely. Using a Victron MPPT solar controller, you can charge your batteries and power loads directly from solar energy.

What battery types are compatible with this setup?

Victron inverters support both lithium and lead-acid batteries. However, lithium is preferred for higher cycle life and efficiency. We always recommend Pytes.

If you need help designing a system or choosing components, feel free to get in touch as we design, supply and install all across the UK. Use the contact form below or give us a call on 01626563563