What fuse should I use for a boat's shore power connection?
My yacht has a blue 16 A shore power inlet and a 230 V socket circuit, battery charger and immersion heater. What size fuse or breaker should protect the connection, and does the marina's breaker provide enough protection?
Answer
A typical UK or European boat with a 230 V, 16 A shore connection uses a 16 A main circuit breaker and 30 mA residual-current protection, with the inlet, cable and onboard wiring rated to suit. Check the boat's electrical diagram and existing protection first: the rating must match the installation's capacity, and the marina's breaker does not replace the boat's own protection.
Check the inlet and wiring
Read the rating moulded into the shore inlet and cable connectors, then check the main breaker and wiring specification. A blue three-pin IEC 60309 connector marked 16 A, 200 to 250 V is common on European sailing yachts and smaller motorboats. Larger boats may have 32 A connections or separate supplies for domestic equipment and air conditioning.
The main breaker must protect the weakest relevant component downstream. A 32 A marina socket does not make a boat with a 16 A inlet suitable for 32 A. Fitting a larger breaker to stop nuisance trips can leave wiring or connectors unprotected.
- 16 A inlet and suitably rated wiring: normally a 16 A main breaker, subject to the boat's design.
- 32 A inlet: a 32 A breaker is appropriate only when the complete installation is designed for that current.
- Unknown wiring or altered installation: establish cable sizes, routing and equipment ratings before selecting protection.
Disconnect shore power and isolate any inverter or generator before opening panels. Have a qualified marine electrician select, install and test mains protection.
Overcurrent and earth-leakage protection
A circuit breaker protects against overloads and short circuits. An RCD detects current leaking away from the intended circuit, including leakage towards earth. You need both functions.
A typical arrangement uses a double-pole main breaker and a 30 mA RCD, or a suitable RCBO combining both functions. The main isolation arrangement should disconnect live and neutral together. The protective earth must remain continuous and must never be fused or switched.
Read both ratings carefully. An RCD marked 40 A / 30 mA can carry up to its rated current under specified conditions and trips on residual leakage at its stated sensitivity. It does not provide 16 A overload protection. A separate breaker is still required unless the device is an RCBO.
Modern chargers, inverters and other electronic appliances can affect the required RCD type. Follow their manufacturers' instructions; a matching amp rating alone is not enough when choosing a replacement.