How do you safely connect shore power to a marine inverter-charger?
I'm upgrading my boat's electrical system and installing a Victron MultiPlus 12/3000 inverter-charger. How exactly do I wire the incoming 230V shore power through it safely without creating a shore-to-ship grounding nightmare or frying my domestic bank?
Answer
To safely connect shore power to a marine inverter-charger, you must route the incoming 230V AC supply through a double-pole RCBO and a galvanic isolator before it reaches the unit's AC input. The inverter-charger's AC output then feeds your onboard 230V consumer unit, ensuring the internal ground relay can automatically manage your neutral-earth bond when disconnected from the dock.
Incoming Shore Power Circuit
The circuit starts at your deck inlet. For a standard 16A UK or European shore supply, use 3-core 2.5mm² marine grade tinned cable (or Arctic grade blue flex) for all 230V AC runs. Always physically unplug the shore power cable from the pontoon bollard before opening any 230V AC junction boxes or inverter covers.
Before the power reaches the inverter-charger, it must pass through two safety devices:
- Galvanic Isolator: Install this in the earth wire immediately after the shore power inlet. Units like the Safeshore Marine 70A model block low-voltage DC stray currents from the marina. This prevents rapid galvanic corrosion of your hull and anodes. Alternatively, use an isolation transformer (like the Victron 3600W) for complete physical separation.
- Incoming RCBO: Fit a 16A, 30mA double-pole RCBO within 0.5 metres of the shore inlet. This protects the cable run to the inverter against overcurrent and earth faults.
Wiring the Inverter-Charger
Modern combi units like the Victron MultiPlus or Mastervolt Mass Combi have clearly marked input and output terminals. Strip your 2.5mm² cable. Crimp on bootlace ferrules to prevent frayed strands. Connect the incoming shore feed to the AC-IN terminals (Live, Neutral, and Earth).
Wire the AC-OUT 1 terminals to your boat's main 230V distribution panel. This output is backed up by the inverter, meaning your sockets stay live if shore power fails. Many units also have an AC-OUT 2 terminal. Use this for heavy loads like a calorifier (water heater) or a dedicated battery charger for a bow thruster. AC-OUT 2 only receives power when shore power is connected. This prevents you from accidentally flattening your domestic battery bank in an afternoon.
Tighten the AC terminal screws to the manufacturer's specified torque, typically around 1.6 Nm. Loose AC connections create high resistance. They are a primary cause of electrical fires on boats.