What a Shore Power Inlet Does

A shore power inlet is the socket on your boat's hull or cabin where you plug in a heavy-duty electrical cord connected to a dock pedestal or land-based power source. It lets you run your boat's air conditioning, refrigerator, water heater, and other 120-volt or 240-volt systems while you're tied up, without running the engine or generator. The inlet is a weatherproof connector that accepts a marine-grade plug, and it's wired directly to your boat's electrical panel and breaker system.

Most recreational boats use either a 30-amp or 50-amp inlet, with 30-amp being standard on smaller cruisers and sailboats, and 50-amp on larger vessels that draw more power. The inlet itself is just the female connector mounted on the boat; the male plug on the cord end stays on the dock side. When you're plugged in, shore power bypasses your battery and generator, which saves fuel and wear on engines while you're stationary.

Key Takeaways

  • Shore power inlets come in 30-amp and 50-amp versions, with the size depending on your boat's electrical system and power demands.
  • The inlet is a weatherproof socket mounted on the hull or cabin that connects to a dock pedestal via a heavy marine-grade cord.
  • Plugging in shore power lets you run air conditioning, refrigeration, and other AC systems without running your engine or generator.
  • Inlets must be installed by a marine electrician and wired through a galvanic isolator and shore power breaker to protect your boat's systems.
  • Corrosion and water intrusion are the most common problems with shore power inlets, so regular inspection and proper sealing are essential.

30-Amp Versus 50-Amp Inlets

A 30-amp inlet is the most common choice for boats under 35 feet and handles a maximum of 3,600 watts of continuous power at 120 volts. It uses a three-prong twist-lock connector (NEMA 3-prong) and is less expensive to install than 50-amp. Most marinas have 30-amp pedestals available, and the cord and inlet hardware are cheaper to replace if damaged. If your boat has a single air conditioning unit, modest refrigeration, and a small water heater, 30-amp is usually sufficient.

A 50-amp inlet handles 12,000 watts at 240 volts and uses a four-prong twist-lock connector (NEMA 4-prong). It's standard on larger cruising sailboats, trawlers, and cabin cruisers over 40 feet, or on any boat with multiple air conditioning units, electric heating, or a large galley. The 50-amp system is more expensive to install and requires a heavier-gauge cord, but it gives you the power to run everything simultaneously without tripping breakers. Not all marinas have 50-amp pedestals, so check availability before upgrading.

Installation and Wiring Requirements

Shore power inlets must be installed by a may have access to marine electrician, not as a DIY project. The inlet is mounted on the hull or cabin side, typically near the waterline or on a cabin wall, and sealed with marine sealant to prevent water intrusion. The wiring runs from the inlet through a galvanic isolator (a device that prevents stray electrical current from corroding your boat's metal fittings) and then to a dedicated shore power breaker in your electrical panel.

The breaker size matches your inlet—a 30-amp inlet gets a 30-amp breaker, and a 50-amp inlet gets a 50-amp breaker. The wire gauge must be heavy enough to handle the current without overheating; a 30-amp system typically uses 10-gauge wire, and a 50-amp system uses 6-gauge or larger. All connections must be made with marine-grade terminals and sealed against corrosion. If your boat is older or has an outdated electrical panel, an electrician may recommend upgrading the entire system before adding shore power.

Common Problems and Maintenance

The most frequent issue with shore power inlets is corrosion around the connector, caused by salt spray, moisture, and the electrical current flowing through the connection. Corrosion increases resistance, which generates heat and can eventually damage the inlet or the cord. To prevent this, rinse the inlet and plug with fresh water after each use, especially in saltwater environments, and apply a thin coat of dielectric grease to the connector pins before plugging in.

Water intrusion into the inlet is the second major problem. If the inlet is not sealed properly during installation or if the sealant cracks over time, water can seep into the wiring and cause short circuits or electrolysis damage. Inspect the inlet regularly for cracks in the sealant, discoloration, or corrosion around the base. If you see any damage, have a marine electrician re-seal it or replace the inlet. Never use the inlet if you notice water inside the connector or if the plug feels loose or corroded.

Blown breakers when you first plug in are usually a sign of a short circuit or a problem with the dock pedestal's power supply. Unplug immediately and do not attempt to reset the breaker repeatedly. Have the inlet and wiring inspected by an electrician before using shore power again. Similarly, if you smell burning plastic or see scorch marks around the inlet, turn off the breaker, unplug, and get professional help.

Choosing a Marina with Compatible Shore Power

Not all marinas offer shore power, and those that do may have only 30-amp pedestals, only 50-amp, or a mix of both. Before booking a slip, confirm that the marina has the amperage your boat needs. If your boat has a 50-amp inlet but the marina only offers 30-amp, you cannot safely use an adapter to step down; you would need to run on battery and generator instead. Some marinas charge a flat daily or monthly rate for shore power, while others include it in the slip fee or charge by the kilowatt-hour.

When you arrive at a marina, inspect the pedestal before plugging in. Look for loose connections, corrosion, water pooling around the base, or burn marks on the outlet. If the pedestal looks damaged or unsafe, ask the dockmaster to inspect it or assign you a different pedestal. Always plug in your boat before turning on any AC loads—this prevents a surge that can damage your systems. Unplug in the reverse order: turn off all AC loads first, then unplug the cord.

Shore Power Cords and Adapters

Marine shore power cords are not the same as household extension cords. They are rated for wet environments, have thicker insulation, and use marine-grade connectors. A 30-amp cord is typically 25 or 50 feet long and costs between $100 and $300, depending on length and quality. A 50-amp cord is heavier and more expensive, usually $200 to $500. Buy a cord rated for the amperage of your inlet—never use a 30-amp cord on a 50-amp inlet or vice versa.

Adapters that convert between 30-amp and 50-amp connectors exist but should only be used as a temporary solution. They do not increase the power available; a 30-amp adapter on a 50-amp pedestal still limits you to 30 amps. Adapters also add connection points where corrosion can occur. If you frequently need a different amperage than your inlet provides, consider having a second inlet installed by a marine electrician, or plan your marina stays around the available power.

Galvanic Isolators and Electrical Safety

A galvanic isolator is a safety device installed between your shore power inlet and your boat's electrical panel. It blocks low-voltage DC current (which causes corrosion of metal fittings like through-hulls and propeller shafts) while allowing the normal AC current to flow. Without an isolator, stray current from the dock's electrical system can find a path through your boat's metal components to the water, corroding them over time—a process called galvanic corrosion.

Most modern boats come with an isolator already installed, but older boats may not have one. If you're adding shore power to an older boat, a marine electrician will include an isolator in the installation. Isolators are not expensive (typically $100 to $300) and are essential for protecting your boat's through-hull fittings, engine block, and other underwater metal. If your boat is moored in saltwater year-round, a galvanic isolator is not optional—it's a requirement for long-term electrical safety.

Frequently Asked Questions

Can I use a household extension cord as a shore power cord?

No. Household cords are not rated for the wet, saltwater environment around a boat, and they lack the heavy insulation and marine-grade connectors that shore power cords have. Using a household cord risks electrical shock, fire, and damage to your boat's systems. Always use a marine-grade shore power cord rated for your inlet's amperage.

What happens if I plug in a 50-amp cord to a 30-amp inlet?

The connectors are different sizes and will not fit together. A 50-amp plug is larger and uses a different twist-lock pattern than a 30-amp inlet. You cannot force them together, and attempting to do so will damage both the plug and the inlet. If you need to use a different amperage, use an adapter or have a second inlet installed.

Do I need to turn off my boat's breaker before unplugging shore power?

Yes. Always turn off all AC loads and the shore power breaker before unplugging the cord. This prevents a surge that can damage your electrical panel and appliances. Unplug the cord last, after everything is off. When plugging in, reverse the order: plug in first, then turn on the shore power breaker, then turn on individual loads.

What should I do if the shore power inlet is corroded?

Stop using it and have a marine electrician inspect it. Light surface corrosion can sometimes be cleaned and treated with dielectric grease, but heavy corrosion usually means the inlet needs to be replaced. Do not attempt to clean it yourself or force the plug in, as this can damage the connector pins and create a fire hazard.

Can I leave my boat plugged into shore power all winter?

Yes, shore power is designed for long-term use. Many boats stay plugged in for months during winter or off-season storage. Make sure the inlet and cord are in good condition, the connection is tight, and the pedestal is functioning properly. Inspect the inlet monthly for corrosion or water intrusion, and keep the connector clean and dry.