Shore Power, Isolation Transformers & Converters

At the dock, shore power runs your air conditioning, appliances and battery chargers without the noise, fuel and maintenance of the generator. It is also the connection where many electrical problems on boats begin: overheated plugs, polarity issues and stray currents that corrode underwater metals.

This guide explains how shore power works, how it compares with generator power, and the equipment that makes it safe: isolation transformers, galvanic isolators and shore power converters.

How Shore Power Works

The marina pedestal supplies AC power through a shore cord to an inlet on the boat, and from there to the main AC panel. Most recreational boats use 30-amp 125-volt service; larger boats and yachts use 50-amp service at 125 or 125/250 volts, sometimes with two cords. Large yachts may use higher-capacity connections.

The weak points are the connections. A worn or loose plug heats up under load and is a common cause of shore power fires. Inspect cords and inlets regularly and replace any that show discoloration, corrosion or melted plastic.

Shore Power vs. Generator

Generators make a boat independent of the dock, and remain essential for cruising and anchoring. At the marina, shore power is usually the better choice:

Quiet: no engine noise or vibration on board or for your neighbors.
Lower cost: no fuel, and fewer generator hours and services.
Cleaner: no exhaust at the dock, which is why more ports and marinas are expanding shore power.
Battery friendly: chargers keep the banks full whenever the boat is plugged in.

Galvanic Corrosion and Stray Current

The shore power ground connects your boat to every other boat on the dock. Through that path, small galvanic currents flow between dissimilar underwater metals and slowly eat zincs, props, shafts and through-hulls. Faults on the dock or on board can add stray current, which corrodes metal much faster.

A galvanic isolator blocks low-voltage galvanic currents on the ground wire while still allowing fault current to flow. It is a cost-effective first line of defense. On many newer boats, ground-fault protection (ELCI) on the main shore power circuit is also part of the standard.

Marine Isolation Transformers

An isolation transformer goes further: it transfers power magnetically, so there is no direct electrical connection between the shore and the boat. That eliminates galvanic and stray current through the shore ground, solves reverse-polarity problems at the pedestal, and gives cleaner power to sensitive electronics.

Isolation transformers are heavy and must be sized for the shore service, but on yachts with valuable underwater metals, aluminum hulls or frequent time at busy marinas, they are one of the best protections available.

Shore Power Converters

Yachts built for 50 Hz power, common in Europe, or that need stable voltage and frequency regardless of the marina supply, use shore power converters. They accept the local shore power and output the voltage and frequency the yacht was designed for, often combining several shore cords into one stable supply.

Atlas ShorPOWER, ANG, EnSmart, ASEA and ProMariner are among the converter systems found on yachts in Fort Lauderdale. Choosing and installing one requires a careful look at the yacht load, the available marina service and the space on board.

Shore Power Service Across South Florida

OnBoat Marine inspects and upgrades shore power systems on site across Broward, Miami-Dade and Palm Beach counties: inlets and cords, AC panels, galvanic isolators, isolation transformers and converters. We also trace stray current and polarity problems.

See our AC/DC electrical panels service, read our inverters and inverter chargers guide, or contact us to schedule an inspection.

Frequently Asked Questions

What is the difference between 30 amp and 50 amp shore power?

A 30-amp 125-volt service supplies about 3,600 watts. A 50-amp service supplies about 6,000 watts at 125 volts or about 12,000 watts at 125/250 volts, enough for larger air conditioning and galley loads.

Why does my shore power plug get hot?

Heat usually means a worn, loose or corroded connection. It is a fire risk: stop using the cord or inlet and have it inspected and replaced.

Do I need an isolation transformer or a galvanic isolator?

A galvanic isolator is a cost-effective protection for most boats. An isolation transformer gives complete isolation and is recommended for yachts with high-value underwater metals or recurring corrosion problems.