Fox ESS Cube battery storage system installation (UK)

Helpful video reference. This video by Alps Electrical shows a Fox ESS Cube installation in a UK property, covering the unboxing, wall fixing, module stacking, AC wiring and Fox Cloud setup. It is a good end-to-end reference before reading the steps below.

1. PAS 63100 site survey and DNO notification

PAS 63100:2022 is the British Standard specification for the installation of electrical energy storage systems in dwellings. It covers location requirements, cable sizing, earthing, fire separation and the documentation your installer must provide.

Before any physical work starts, the installer should:

• Assess the proposed location -- an internal wall in a utility room, garage or under-stairs space is typical. The Fox ESS Cube requires adequate ventilation and must not be installed in a room used for sleeping.
• Confirm the earthing arrangement (TN-C-S, TN-S or TT) and check the consumer unit has a way available for the battery circuit.
• Submit the required DNO notification. Systems with total inverter capacity up to 3.68kW (single phase) can use the simpler G98 notification, submitted at least 28 days before commissioning. Larger systems require a G99 application, which may need DNO approval before work begins.

2. Choose AC or DC coupling and select the location

The Fox ESS Cube can be configured in two ways:

• AC coupling connects the Cube's built-in inverter to the AC output of any existing solar inverter. This is the most common configuration for retrofit installations because it works with any brand of solar inverter already fitted.
• DC coupling connects the battery modules directly to the DC side of a compatible Fox ESS hybrid inverter. This is more efficient (energy is converted once rather than twice) but requires a Fox ESS inverter -- it will not work with a SolarEdge, Solis, GivEnergy or other third-party brand.

For most homeowners adding battery storage to an existing system, AC coupling is the practical choice. If you are starting from scratch with new solar panels, DC coupling with a Fox ESS hybrid inverter is worth considering for the efficiency gain.

Choose an installation location that is cool (under 45°C ambient), well-ventilated, dry and accessible for future servicing. The Fox ESS Cube is not suitable for outdoor installation or loft spaces without thermal management.

3. Mount the Cube cabinet and battery modules

The Fox ESS Cube uses a wall-bracket mounting system. Fix the steel bracket to the wall using rawlbolts or suitable fixings for the wall type -- the combined weight of the cabinet and a full stack of modules can exceed 100kg, so the fixings must be rated for the load.

Hang the Cube cabinet on the bracket and, working from the bottom up, slide each battery module into the cabinet and secure it with the retaining bolts. Connect the bus-bar links between modules exactly as shown in the installation manual -- incorrect stacking order or a loose bus-bar is a safety issue.

Connect the high-voltage DC cable between the battery stack and the inverter section according to the colour coding in the Fox ESS documentation. These cables carry significant DC voltage -- treat them with the same care as any high-voltage conductor.

4. AC wiring and CT clamp installation

The Fox ESS Cube inverter section connects to the consumer unit via a dedicated AC circuit, sized for the inverter's rated output. In most UK homes this is a 6mm² twin and earth cable protected by a 32A MCB or RCBO.

The CT clamp is the key metering component. It clips around the main import/export cable at the meter tails or as close to the meter as possible, before any branch circuits. The CT clamp tells the Fox ESS Cube how much power the house is currently importing or exporting, allowing the battery to charge or discharge to reach a target import level (typically zero -- the system tries to make you energy self-sufficient in real time).

Thread the CT clamp cable through the cabinet entry and connect it to the designated port on the Fox ESS gateway. Note the directional arrow on the CT clamp -- pointing in the wrong direction inverts the sign of the reading, causing the battery to do the opposite of what you want.

5. DNO export limit configuration

Before commissioning, set the inverter's export power limit to the value agreed in your G98 notification or G99 approval. For most single-phase G98 installations this is 3.68kW. If you are not exporting at all (battery charges from grid only), set the export limit to zero.

This parameter is set in the Fox ESS inverter menu or via Fox Cloud once the gateway is online. Your installer should document the setting on the commissioning sheet and include it in the handover pack.

6. Fox Cloud commissioning and app setup

Energise the system and wait for the Fox ESS gateway to boot. Connect the gateway to your home Wi-Fi via the Fox Cloud setup process:

1. Download the Fox ESS app and create an installer or owner account.
2. Enter the inverter serial number to register the device on Fox Cloud.
3. Connect the gateway to Wi-Fi -- the app guides you through the process.
4. Set the battery charging and discharging schedule. A common setup is to charge from the grid during the cheap overnight window (midnight to 5am on Octopus Go, for example) and discharge during the peak-rate evening.
5. Verify the CT clamp reading is sensible -- the Fox Cloud dashboard shows a live power flow diagram. Import should show as positive and export as negative (or vice versa, depending on firmware). A reading that is obviously wrong (solar panels shown as importing, for example) usually means the CT clamp direction is inverted.

Run the system for at least 24 hours and confirm that scheduled charging and discharging work correctly before handing over the commissioning documentation.

When to call us

Battery storage installations involve Part P notification, PAS 63100 compliance and DNO paperwork. Richard covers east Kent and can advise on whether a Fox ESS Cube is the right fit for your existing solar system, or whether a GivEnergy, Powerwall or other brand would suit better.