Marine Electric Systems designs and installs marine shore power systems for sailing yachts, catamarans, and motor yachts throughout the Chesapeake — Annapolis, Baltimore, and the greater Washington DC area. A properly engineered shore power system is more than a plug at the marina pedestal: it's a full chain of inlet, GFI protection, galvanic isolation or isolation transformer, and AC distribution that delivers safe, clean, properly grounded power to your boat — and protects your boat's underwater hardware from stray-current corrosion.

What's included in a marine shore power install

• SmartPlug shore power inlet — 30A/125V, 50A/125-250V, or 100A/250V depending on boat size and AC load; significantly more reliable than legacy twist-lock standards
• GFI shore power breaker — per ABYC requirements, in a marine-grade enclosure within 10 feet of the inlet
• Marine-grade shore cable — 6/3 for 50A, 8/3 for 30A, properly sized to the load
• Galvanic isolator OR isolation transformer — ProMariner ProSafe FS for galvanic protection on most boats; isolation transformer (Victron, ASEA IsoBoost) for full electrical isolation on boats that need it
• AC main panel and breakers — Blue Sea Systems with proper double-pole breakers for major loads (water heaters, AC, dryers) and single-pole branch circuits
• Reverse polarity and ground fault detection — indicators at the AC panel
• Inverter/charger AC integration — with Victron MultiPlus or Quattro for seamless transfer between shore, generator, and battery
• Auto Transformer for 120/240V split-phase — if needed, for boats running 240V loads on a 50A shore connection
• Bonding and grounding — verified throughout, ABYC-compliant
• As-built documentation — AC system schematic, full system test, and an owner walkthrough

Why the SmartPlug matters

The legacy 30A and 50A twist-lock shore power inlets fail in two predictable ways: corrosion at the contacts, and heat from poor contact pressure under load. Both lead to the same outcome — melted plugs, charred wiring, and in the worst case, dock fires. The SmartPlug design eliminates both failure modes with a sealed, push-and-twist connection and proper contact pressure. We install SmartPlug inlets on every shore power upgrade because the safety improvement is real and the cost difference is small.

Galvanic isolator vs isolation transformer

Both protect your boat from electrolytic corrosion via the AC ground path — but they work differently and serve different needs.

Galvanic isolator (ProMariner ProSafe FS or equivalent): blocks low-voltage DC galvanic currents that flow through the marina ground, while passing AC ground for safety. It's compact, inexpensive, and the right answer for most cruising boats. Critical on catamarans with two saildrives sharing a marina ground.

Isolation transformer (Victron Isolation Transformer, ASEA IsoBoost): fully isolates your boat's AC system from the marina supply via magnetic coupling. Eliminates galvanic and ground-loop concerns completely. Some models also boost low or unregulated marina voltage to a stable 120V or 240V — useful in older marinas with marginal power. Heavier and more expensive than a galvanic isolator, but the best protection available.

30A, 50A, or 100A — sizing the shore service

• 30A / 125V (3,600W): right for boats up to about 35 feet without electric water heaters, AC, or other heavy AC loads. Limits inverter/charger to MultiPlus 3000W maximum.
• 50A / 125-250V (12,000W): the standard for cruising boats from 35 to 60 feet with AC, electric water heaters, and watermakers. Pairs well with Quattro 5000W inverter/chargers.
• 100A / 125-250V (24,000W): for large motor yachts and catamarans with multiple AC zones, electric ranges, dryers, and dual inverter/chargers in parallel.

Brands we install

We are brand-agnostic on shore power components. SmartPlug is our default for inlets. ProMariner ProSafe FS series is our default for galvanic isolators. Victron Isolation Transformer and ASEA IsoBoost are our usual choices for isolation transformers. AC distribution panels are typically Blue Sea Systems for breaker quality and modular flexibility.

Recent shore power projects

Shore power upgrades are part of every full electrical refit we do. Recent examples on the Chesapeake:

• Leopard 48 catamaran Tortuga — 50A SmartPlug shore inlet with 50A GFI breaker, ProMariner ProSafe FS60 galvanic isolator, 6/3 marine cable, and Victron Auto Transformer for 120/240V balancing

For more on how shore power integrates with a full electrical platform, see our marine inverter/charger and lithium battery installation pages.

Service area

Marine Electric Systems serves cruising sailboats, motor yachts, and catamarans throughout the Chesapeake region: Annapolis, Baltimore, the Eastern Shore, the greater Washington DC area, and the surrounding Maryland and Northern Virginia waterfront. We work at marinas, boatyards, and private docks across the region.

Frequently asked questions

Do I really need a galvanic isolator?

If your boat has any underwater metal hardware (props, shafts, struts, saildrives, bronze through-hulls) and you spend time at marinas, yes. Galvanic corrosion through the marina ground is real and expensive. A galvanic isolator is cheap insurance against having to replace underwater hardware.

What's the difference between a galvanic isolator and an isolation transformer?

A galvanic isolator blocks low-voltage galvanic currents while passing AC ground. An isolation transformer fully isolates your AC system magnetically — no electrical connection at all between marina and boat. Isolation transformers are the gold standard but cost more and weigh more. Most cruising boats are well-served by a quality galvanic isolator.

Can I upgrade from 30A to 50A shore service?

Usually yes — it requires a new inlet, new GFI breaker, new shore cable, and often AC panel rework to handle the higher current. Worth doing on boats adding AC, watermakers, or larger inverter/chargers. We scope the upgrade during planning.

How long does a shore power upgrade take?

A standalone shore inlet, GFI, and galvanic isolator install typically takes 2 to 4 days. Adding an isolation transformer or full AC panel rework adds another 2 to 5 days. As part of a full electrical refit, shore power work integrates into the wider 1 to 3 week timeline.

What is the IsoBoost transformer for?

An IsoBoost (ASEA) is an isolation transformer that also automatically boosts low marina voltage — useful at older marinas where the supply runs 105-110V instead of a clean 120V. It protects sensitive electronics from undervoltage damage and ensures inverter/chargers and AC equipment get clean power.

Get in touch

If you're considering a shore power upgrade or a full electrical refit on a sailboat, motor yacht, or catamaran in the Annapolis, Baltimore, or Washington DC area, get in touch. We'd be happy to scope the project, walk you through what's involved, and recommend the right combination of inlet, isolation, and AC distribution for your boat.