The Fox ESS EPS 3PH-4UNIT is a three-phase parallel and backup box built for residential and commercial solar installations. It connects the EPS (off-grid) outputs of up to four Fox ESS three-phase inverters to a single load output, so several units can share one backed-up supply, and it switches automatically between on-grid and off-grid operation.
Rated for 80A per phase on both the grid input and the load output, it carries four dedicated EPS inputs at 20A per phase each, plus a COM port for the inverter link. The IP65-rated robust metal enclosure is wall-mounted, naturally cooled and supplied with brackets and fixings for straightforward installation.
80A
Max per phase (grid input / load output)
4
Inverters in parallel (EPS-1 to EPS-4)
20A
Max per phase, each EPS input
IP65
Robust metal enclosure
-25 to +50 °C
Operating temperature
336 x 306 x 138 mm
Dimensions (W x H x D)
How it works
Each inverter's EPS (off-grid) output connects to its own port (EPS-1 to EPS-4), the mains supply connects to GRID, the protected circuits connect to LOAD, and the host inverter's communication link connects to COM. With everything connected, the box handles the automatic parallel and off-grid switching between the machines.
Compatibility: check your inverter before ordering
Designed for Fox ESS three-phase H3 and AIO-H3 inverters only. It is not compatible with the H3 Smart or H3 Pro and is not intended for single-phase systems.
Qualified electrician required
Only authorised, qualified personnel may wire this unit. Disconnect the circuit-breaker on all phases and secure it against re-connection before working, check the grid voltage against the permitted range, and follow the manufacturer's manual and current UK wiring regulations (BS 7671).
Key Features
Parallel up to 4 inverters
Enables off-grid parallel operation of up to four three-phase H3 / AIO-H3 units from one box, with a single grid connection and a single load output.
Automatic switching
Automatically switches between on-grid and off-grid state, handling the changeover between mains and inverter EPS supply without manual intervention.
80A per phase
80A maximum per phase on the grid input and on the load output, suited to three-phase residential and commercial loads.
Four EPS inputs
Four groups of EPS inputs (EPS-1 to EPS-4), each rated 20A per phase at 220/380 or 230/400 VAC, 3L/N/PE, 50/60 Hz.
IP65 metal enclosure
A robust metal enclosure with IP65 ingress protection gives dust-tight, water-jet protection, with an operating range of -25 to +50 °C.
Easy wall mounting
Wall-mounted with natural cooling (no fan). Four mounting brackets, expansion tubes and screws, an earth terminal and the connector plugs are included.
Technical Specifications
General
Type
Three-phase EPS parallel / backup box
Compatible inverters
Fox ESS H3 and AIO-H3 (three-phase)
Max. inverters in parallel
4
Communication (COM)
Meter / RS-485 interface
Grid Input
Rated voltage
220/380 VAC, 230/400 VAC, 3L/N/PE
Max. input current (per phase)
80A
EPS Input (from inverters)
Rated voltage
220/380 VAC, 230/400 VAC, 3L/N/PE
Max. input current (per phase)
20A per input
Number of groups
4 (EPS-1, EPS-2, EPS-3, EPS-4)
EPS Load Output
Rated voltage
220/380 VAC, 230/400 VAC, 3L/N/PE
Max. output current (per phase)
80A
Mechanical and Environmental
Installation
Wall-mounted
Operating temperature range
-25 to +50 °C
Dimensions (W x H x D)
336 x 306 x 138 mm
Packing dimensions (W x H x D)
440 x 345 x 205 mm
Installation Requirements
Minimum clearance: left / right / top
300 mm
Minimum clearance: bottom
500 mm
Mounting surface
Solid brick or concrete, or equivalent strength
Fixing holes
8 mm diameter, at least 50 mm deep
Maximum altitude
Approx. 2000 m above sea level
Site conditions
Out of direct sunlight, rain and snow; not in potentially explosive areas or humidity above 95%
Supplied in the Box
Brackets
4 x mounting brackets
Connectors
1 x LOAD, 1 x GRID, 1 x COM, 4 x EPS
Fixings
Expansion tubes and screws, 9 x hexagonal screws
Earthing
1 x earth terminal
Documentation
Product manual
Dimensions and weight: source note
Dimensions and weights above follow the current manufacturer datasheet (V1.4, March 2025). The earlier user manual (V1.1) lists 402 x 306 x 138 mm and 2.8 kg net. Confirm the wall space and the delivered unit against the datasheet before installation.
Frequently Asked Questions
Which Fox ESS inverters does the EPS 3PH-4UNIT work with?
It is an accessory for the three-phase H3 and AIO-H3 inverters. It is not compatible with the H3 Smart or H3 Pro, and it is not for single-phase systems.
How many inverters can I connect?
Up to four three-phase inverters, one per EPS port (EPS-1 to EPS-4). Each EPS input is rated at 20A per phase. The units are first linked for communication, then each inverter's off-grid output goes to its EPS port.
What does the COM port connect to?
The COM port takes the Meter / RS-485 connection from the host inverter, including the relay-control, +12V and ground signals taken from the meter port of the H3. Follow the pin definitions in the manual when wiring.
Can it be installed outdoors?
The IP65 metal enclosure and -25 to +50 °C operating range suit demanding locations, but the manufacturer still specifies a site out of direct sunlight, rain and snow, with good ventilation and humidity below 95%.
What space and wall strength do I need?
Leave at least 300 mm to the left, right and above and 500 mm below. Mount on solid brick, concrete or an equivalent surface using the supplied brackets and expansion fixings (8 mm holes, at least 50 mm deep). Weaker walls must be supported or strengthened.
Who should install it?
A qualified electrician. Only authorised personnel should make the connections, all phases must be isolated and secured against re-connection before wiring, and the installation must follow the manufacturer's manual and UK wiring regulations (BS 7671).
