I’ve designed this Victron system with a MCS electrician. We loosely built using the UK Offgrid Systems Cube system as a template. Which as the name says was an off grid system. The design we’ve created is an on grid system. I look forward to getting your feedback.
System Overview:
A three-phase Energy Storage System (ESS) using Victron components, configured for zero export initially, with a total battery capacity of 35kWh (48V nominal). The system is designed for robust performance, safety, and compliance with UK regulations.
1. DC Power System & Batteries
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Battery Bank:
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Chemistry: Lithium Titanate Oxide (LTO).
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Configuration: Fifteen 48V/50Ah batteries arranged in three independent 5-battery strings.
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Safety: Each individual battery is protected by a 100A marine fuse and a DC 125A isolator switch.
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DC Wiring & Distribution:
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String Level: Each battery string uses 35mm² cables of equal length to connect to its own dedicated copper busbar.
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Main DC Bus: The three string busbars are connected to a central set of large copper busbars using 95mm² cables.
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Protection: Each 95mm² positive cable is protected by a 250A Class-T fuse.
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Monitoring: A Victron PowerShunt on the main negative busbar provides state-of-charge and power data to the Cerbo GX.
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Inverters/Chargers:
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Units: Three Victron Quattro 48/10000/140 inverters.
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Connection: Each Quattro is connected to the main DC busbars via 120mm² cables.
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Protection: Each positive cable to a Quattro is secured with a 400A Mega fuse and a high-current DC switch.
2. AC Power Path & Grid Connection
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AC Input (Grid Side):
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Grid Connection: 25mm² cable enters a 125A 4-pole isolator.
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Grid Monitoring: A ZIEHL UFR1001E monitor controls an ABB AF65-30-00-13 contactor based on grid health.
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Distribution: Power flows to a distribution board with 63A MCBs, which feed the three Quattro inverters via 16mm² cables.
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Energy Metering: A Victron ET340 energy meter, with Carlo Gavazzi TAD3 current transformers (CTs) on each phase, communicates with the Cerbo GX for ESS control.
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AC Output (Load Side):
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Safety Monitoring: A Bender RCM423 insulation monitor, with Siemens CTs and a co-located Bender W35 core balance CT, provides earth fault and RCD protection.
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Control: Power passes through an ABB AF52 contactor.
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Final Distribution & Protection: The output is secured by a 63A 3-pole MCB, a MK Sentry surge protection device (SPD), and a final 63A isolator before connecting to the house loads.
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System-Wide AC Notes:
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All three-phase wiring maintains correct phase sequence (L1, L2, L3) and uses UK colour-coding.
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All AC neutral conductors are consolidated onto a single copper busbar for efficient distribution.
3. Control, Monitoring & Configuration
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System Controller: Victron Cerbo GX Mk2.
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Operational Mode: Configured for Energy Storage System (ESS) with Zero Export to the grid.
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Monitoring:
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Victron VRM: Enabled for remote monitoring via the VRM app with push notifications.
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CT Orientation:
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Grid CTs (Carlo Gavazzi): “K” mark facing towards the grid.
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Load CTs (Siemens/Bender): “K” mark facing towards the house loads.
4. Mechanical & Safety Compliance
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Cable Management: All cables are securely fastened with P-clips at ~150mm intervals, including support for bends.
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Terminations:
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High-Current (Lynx): M10 bolts torqued to 30 Nm.
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Standard Busbars: M8 bolts torqued to 18 Nm.
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UK Compliance:
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Export Limit: System export power is hard-limited to 16.5kW.
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Grid Draw: The design ensures total draw from the grid remains below the UK standard 100A fuse limit