If your boat lives at a marina, the shore power cord does more work than almost any other piece of gear aboard. It runs battery chargers, air conditioning, water heaters and refrigerators, often for days at a time, in a wet and salty environment. When it's in good shape you never think about it. When it isn't, the result can be a melted plug, a dockside fire, or worse.
This guide explains the difference between 30 amp and 50 amp marine shore power, when adapters make sense, how to inspect your cord and inlet, and the safe order for plugging in and unplugging.
Quick answer
- Most smaller boats with shore power use 30 amp, 125-volt service; larger boats often use 50 amp service, which may be 125 V or 125/250 V depending on the boat.
- Use a marine-rated shore power cord matched to your boat's inlet. Household extension cords aren't designed for this.
- Adapters can be useful, but they don't increase available power. A 50A boat on a 30A pedestal must limit its load.
- Inspect plugs and the boat inlet for heat discoloration, corrosion and loose fit regularly. Brown or melted contacts mean replace now.
- Never swim near docks with shore power. Electric shock drowning is a real risk around marinas.
30 amp vs 50 amp basics
| 30 amp marine | 50 amp marine | |
|---|---|---|
| Typical voltage | 125 V | 125 V or 125/250 V (check your boat) |
| Typical boats | Small to mid-size cruisers, sailboats, houseboats with modest loads | Larger boats with multiple AC units, electric galleys, big loads |
| Cord gauge | Lighter | Heavier and stiffer |
| Plug | Locking marine connector | Larger locking marine connector |
Some boats have two 30 amp inlets that power separate circuits. Look at your boat's inlet label and electrical panel to know exactly what you have. If you're not sure, check the owner's manual or ask a marine electrician.
Choosing a shore power cord
- Marine-rated: designed for wet environments, with locking connectors and a weather-resistant jacket
- Correct amperage and configuration for both the pedestal and your boat's inlet
- Length: long enough to reach the pedestal with slack for tides and boat movement, but not so long you coil large amounts on the dock
- Sealing collars or weatherproof covers at the boat-end connector
- Visible indicator lights on some cords show power at the connector, which is handy for troubleshooting
Coiled excess cord can build up heat under high load. Use a length that fits your slip, and avoid leaving a big coil on the dock while running heavy loads.
Adapters: when they're fine and when they're not
Marinas don't always have the pedestal you need. Adapters let you connect a 30A cord to a 50A outlet, a 50A boat to a 30A outlet, and so on. They're widely used and can be perfectly safe when they're marine-rated and used correctly. A few points matter:
| Situation | Notes |
|---|---|
| 30A boat on a 50A pedestal | Use a marine adapter; your boat still draws no more than its 30A system allows |
| 50A boat on a 30A pedestal | You have much less power available. Run only essential loads or the pedestal breaker will trip; never bypass it |
| 50A 125/250V boat on 125V service | Some adapters and boat systems handle this differently. Check your boat's manual and the adapter instructions; 240V appliances may not work |
| Household outlet adapter | Only with a product designed for it, and only for light loads like a battery charger; GFCI outlets may trip |
| "Y" or splitter adapters | Used to combine or split services; follow instructions carefully and confirm with a marine electrician if unsure |
The real failure point: heat at the connections
Most shore power problems start at a connection, not in the cord's length. A slightly loose or corroded contact has more resistance, which creates heat under load. Heat makes the corrosion worse, which creates more heat. Eventually the plastic browns, softens, and can melt or catch fire.
What to look for
Discoloration
Brown or black marks around contacts on the plug, connector or boat inlet.
Loose fit
The plug doesn't seat firmly, or the locking ring won't tighten fully.
Corrosion
Green or white crust on blades or in the receptacle.
Warmth
Plug or inlet feels warm after running loads for a while.
Any of these means it's time to replace the connector, cord end or inlet. Replacing only one side of a damaged connection often leads to the new part failing too, since heat damage on one side harms the other. Have a qualified marine electrician check both the boat inlet and cord when you see heat damage.
Safe order for connecting and disconnecting
- Turn off the pedestal breaker and the boat's main shore power breaker.
- Connect the cord to the boat first, then to the pedestal. That way you never handle a live cord end near the water.
- Lock the connectors and fit any weather collars.
- Turn on the pedestal breaker, then the boat's main breaker.
- Check the boat's panel for reverse polarity indication if your boat has it.
- To disconnect, reverse the order: boat breaker off, pedestal breaker off, unplug at the pedestal first, then the boat.
Electric shock drowning: why it matters
When electrical current leaks into fresh water from a faulty boat or dock, a swimmer nearby can be paralyzed by the current and drown. This is known as electric shock drowning, and it's a recognized hazard around marinas, especially in fresh water.
- Never swim near marinas, docks or boats connected to shore power
- Keep your boat's AC system inspected and in good repair
- Ask whether your boat and the marina use ground fault or equipment leakage protection; newer standards call for these protections in various places
- If someone in the water near a dock feels tingling or shocks, tell them to swim away from the dock; don't jump in after them. Shut off power and call for help
Leaving the boat plugged in unattended
Many owners leave shore power connected all week to keep batteries charged and run a dehumidifier or refrigerator. That's normal, but it puts more weight on everything above being right.
- Use a marine battery charger designed for continuous connection, with appropriate charge profiles for your batteries
- Avoid leaving space heaters or other high, continuous loads running unattended unless they're designed and installed for that use
- Check the cord and connectors every visit; touch the plug to feel for warmth
- Make sure the cord can't fall in the water or be pinched as the boat rises and falls
- Know whether your marina has rules about unattended appliances or connected boats
If you only need to keep batteries topped up, a solar maintainer may let you leave the boat unplugged. Our guide to sizing a solar battery maintainer explains how.
Cord care and storage
- Keep connectors off the dock surface and out of water
- Avoid kinks and sharp bends; don't run the cord where it can be pinched by the boat or dock
- Rinse salt off connectors occasionally and let them dry fully
- Store coiled loosely in a dry place when not in use
- Replace cords with cracked jackets, damaged strain reliefs, or heat-marked plugs
FAQ
Can I use a regular extension cord for shore power?
Household extension cords aren't designed for marine use, locking connections or continuous heavy loads in wet conditions. Use a marine-rated shore power cord.
Can a 50 amp boat plug into 30 amp?
With a proper marine adapter, often yes, but you'll have much less power available. Run only essential loads and never bypass a breaker. Check your boat's manual for its specific configuration.
Why is my shore power plug turning brown?
Brown or black marks usually mean heat from a loose or corroded connection. Replace the damaged parts and have both the cord and boat inlet inspected.
Why does my shore power keep tripping the GFCI?
There may be current leakage somewhere in the boat's AC system, or a fault in an appliance or charger. Have a marine electrician find the cause rather than avoiding GFCI-protected outlets.
Is it safe to swim near my boat at the marina?
Swimming near docks and boats connected to shore power is widely discouraged because of electric shock drowning risk. Swim well away from marinas.
Bottom line
A marine-rated cord matched to your boat, the right adapters used correctly, regular checks for heat and corrosion at every connection, and a safe plug-in order cover most shore power risk. Add a firm no-swimming rule around docks and an inspection from a qualified marine electrician if you see heat damage or nuisance tripping.