Shore power is electricity supplied from land to a vehicle or vessel that would otherwise generate its own power. When a cruise ship plugs into the electrical grid at port, when a boat connects to a pedestal at a marina, or when an RV hooks up at a campground, they’re all using shore power. The concept is the same in every case: stop running engines or generators and draw cleaner, quieter electricity from an external source instead.
How Shore Power Works for Boats
At a marina, shore power comes from a metal pedestal mounted on the dock. A typical pedestal contains several receptacle options (commonly 30-amp and 50-amp outlets, plus a standard 20-amp household-style outlet), along with water valves, a light, and circuit breakers. You run a heavy-duty shore power cord from your boat’s inlet to the appropriate receptacle on the pedestal, and landside electricity flows into your onboard electrical panel.
Once connected, your boat’s air conditioning, refrigerator, battery charger, water heater, and outlets all run on grid electricity. This means you can keep the cabin comfortable overnight without running a generator, which saves fuel and keeps the marina quiet.
How Shore Power Works for RVs
RV shore power follows the same principle. Campgrounds and RV parks provide electrical hookups, and your rig plugs in through a dedicated cord. The two standard service levels are 30-amp and 50-amp, and the difference matters more than most people realize.
A 30-amp RV has a single 120-volt feed, giving it roughly 3,600 watts of total capacity. That’s enough for basic appliances, but running the air conditioner and microwave at the same time will likely trip the breaker. A 50-amp RV has two separate 50-amp, 120-volt feeds, which provides about 12,000 watts. That’s enough to run multiple air conditioners, a washer/dryer, and kitchen appliances simultaneously. Both service levels operate at 120 volts; the difference is simply how much current (and therefore total wattage) the connection can deliver.
If your RV has a 50-amp plug but the campsite only offers 30-amp service, adapters exist. You’ll just have significantly less power available, so you’ll need to manage which appliances run at the same time.
Shore Power for Commercial Ships
When large cargo or cruise ships use shore power, the process is called “cold ironing.” The term dates back to the age of steam, when a ship’s iron engines would literally go cold at port. Today it means the ship shuts down its diesel generators and plugs into the port’s electrical grid to keep onboard systems running: lighting, ventilation, refrigeration, cargo equipment, and crew quarters.
The engineering challenge is bigger than it sounds. Most ships run their internal grids at 60 Hz, while the local power grid in much of Europe and Asia operates at 50 Hz. Ports handle this mismatch with large frequency converters that adjust the grid electricity to match the ship’s requirements. The international standard governing these high-voltage connections (IEC/IEEE 80005-1) sets requirements for both the shipboard and shoreside equipment.
Environmental Benefits
The environmental case for shore power is strong, especially in the commercial shipping world. Ships at berth traditionally run auxiliary diesel engines around the clock, pumping exhaust into port cities. Connecting to the grid instead reduces ship emissions by roughly 48 to 70% during a port stay, depending on the vessel and the local electricity source. Shore power is particularly effective at cutting nitrogen oxide emissions, which contribute to smog and respiratory problems in communities near busy ports. It also eliminates the noise and vibration that running generators produce.
Even at the recreational scale, shore power reduces pollution. A boat or RV drawing grid electricity instead of running a gasoline or diesel generator produces far less localized exhaust and noise.
Safety Concerns With Shore Power
Shore power introduces electrical risks that don’t exist when a boat or RV is running independently. Two deserve particular attention: electrical shock in the water and galvanic corrosion.
Electric Shock Drowning
In a properly working system, the current flowing through the hot wire and the neutral wire stays balanced. When a shore power cord is damaged or the boat’s wiring has a fault, current can leak into the surrounding water. Swimmers near the boat may feel a paralyzing jolt that causes loss of muscle control, leading to drowning. This is rare but deadly.
Two protective devices guard against it. Ground Fault Circuit Interrupters (GFCIs) monitor individual circuits and cut power instantly if they detect current leaking where it shouldn’t. Equipment Leakage Circuit Interrupters (ELCIs) do the same thing but protect the entire boat at the main shore power connection, tripping at just 30 milliamps of fault current. The American Boat and Yacht Council requires both devices on all boats with shore power connections.
Galvanic Corrosion
Plugging into shore power creates an electrical path between your boat, the dock’s grounding system, and the water. A small natural voltage difference (as little as 0.1 volt) between a metal hull and the surrounding water can drive a slow, steady current that corrodes underwater metals: the hull, propeller, shaft, and through-hull fittings. Simply disconnecting the ground wire would stop this, but that creates a far more dangerous situation by removing the safety ground.
The proper fix is a galvanic isolator, which blocks the low-voltage galvanic current while still allowing the safety ground to function during a real electrical fault. An isolation transformer is a more thorough (and expensive) solution that completely separates the boat’s electrical system from the shore system.
Smart Shore Power Equipment
Traditional shore power connectors use a twist-lock design that can loosen over time, creating resistance and heat at the connection point. Newer “smart” connectors address this with features like a wider blade design for better contact and built-in thermal sensors. The SmartPlug system, for example, monitors the temperature at the connection and automatically cuts power if it reaches 200 degrees Fahrenheit, then restores it once the connector cools to 120 degrees. Overheated connections are a leading cause of boat fires at the dock, so this is a meaningful safety upgrade for any vessel that spends extended time on shore power.