Shore power puts 230V mains electricity, sourced from a shared marina supply, onto a boat sitting in water alongside dozens of other boats on the same earth. That combination carries risks that do not exist in a house, and marina fires and electric shock incidents involving boats are almost always traceable to a small number of recurring causes.
None of the checks below require special equipment, and most take a couple of minutes. The point is not to be alarmed by shore power, which is safe when properly installed and maintained, but to know what a healthy system looks like so a developing fault gets caught early.
The shore power lead is the single most common source of trouble because it lives outside, gets stepped on, coiled tightly, and plugged and unplugged in wet conditions far more often than any other cable on the boat. A blackened or discoloured connector, a pin that feels loose, or a lead that is warm to the touch under load are all reasons to stop using it immediately rather than carry on and monitor it.
Marina-standard connectors are rated for outdoor marine use and should lock positively into both the pedestal and the boat's inlet. A connector that can be pulled apart without releasing the locking ring is worn and should be replaced, not taped or forced.
An RCD (residual current device) or ELCI (equipment leakage circuit interrupter) monitors for current leaking to earth, which is what happens when a person receives a shock or when insulation has failed and current is finding a path through the hull or water. It is one of the few pieces of protection standing between a wiring fault and a fatal shock, and it should be tested regularly using its own test button, not assumed to be working because the lights are on.
Many older boats, and boats fitted out abroad, have marginal or absent RCD protection on the shore power circuit. This is one of the most common findings on a pre-purchase survey and is not expensive to correct, so there is little excuse for leaving it.
Connecting to shore power ties your boat's earth to every other boat on the same pontoon supply through the AC earth conductor. Where a neighbouring boat has more noble underwater metal than yours, this shared earth accelerates corrosion of your anodes, shaft and skin fittings, a galvanic corrosion problem caused directly by the shore connection.
A galvanic isolator, or the more thorough isolation transformer, breaks or isolates that shared earth path while still passing the protective earth needed for safety. Boats that eat anodes far faster after a berth change are frequently missing this protection.
Inside the boat, the AC consumer unit should have individually fused circuits, a clear polarity indicator, and ideally a polarity reversal warning light or lockout, since marina supplies do occasionally have live and neutral reversed. Running equipment on reversed polarity is not always dangerous in itself but it does defeat some protective assumptions built into appliances and switches, so it should be corrected rather than ignored.
A reverse polarity light that is permanently lit, or one that nobody on board has ever checked, both point to the same underlying issue: the AC system needs a proper look.
Tripping breakers that reset and trip again, a persistent smell of hot plastic near the inlet or consumer unit, visible corrosion inside the shore power inlet, or an RCD that will not hold when tested are all reasons to stop using shore power until the system has been checked. Continuing to reset a tripping RCD is treating a symptom of a genuine fault as an inconvenience.
Yes, provided the installation is sound, RCD protected and regularly checked. The risks described here are about identifying faults early, not avoiding shore power altogether.
Every time you connect to shore power is ideal using the built-in test button, with a proper inspection at least annually.
Very possibly. Different marinas have different mixes of boats and metals sharing the earth, and a galvanic isolator or isolation transformer is the usual fix.
No. It is not a substitute for correctly rated marine-grade protection installed as part of the boat's AC system, and it does not address polarity, isolation or connector condition.
Disconnect it, let it cool, and inspect the connectors for damage before using it again. A warm lead under normal load usually means a poor connection or an overloaded circuit.
We check RCD protection, isolation, connectors and polarity as standard on every shore power inspection, and correct anything that falls short.