Shore Power Cord Ends: How to Judge a Cord, and When to Replace the Plug or the Whole Cord

Main breaker on the boat off, pedestal breaker off, then unplug the dock end first and the boat end second. Practical Sailor's surveyor also says to make sure a generator or inverter can't feed the boat's AC panel while you work. Lay the cord out straight on a dry dock or deck.

With a dry rag, feel the cord from end to end. Cuts, cracks, flattened or crushed spots, tape repairs, splices or stiff, discolored sections mean the cord is done, whatever the ends look like. Practical Sailor says to always replace cords with chafe, cracks, split insulation or tape repairs. A cord that has been run over, pinched in a hatch or chewed by chafe isn't worth re-ending.

Under a good light, look at the blades, the pins and the plastic face around them:

• Good: bright metal blades, clean light-colored plastic, no gaps or cracks.
• Warning: brown or black around one blade, blue or rainbow-colored metal, pitted or green-crusted blades, softened or blistered plastic.
• Replace now: melted plastic, a blade that's loose or sunk into the face, a burned hole.

BoatUS has long advised replacing a cord at the first sign of wear on the cord or pitting on the plug blades, and its fire-claim files show most AC electrical fires start somewhere between the marina pedestal and the boat's inlet.

The locking ring holds the connector in the inlet and keeps water out. Look for cracks, broken threads or a ring that won't spin. Check the rubber boot or sealing flange around the plug body, and the point where the cord enters the plug: the jacket should be gripped firmly, with no copper or inner insulation showing. Practical Sailor says industry standards call for shore cords with molded-on plugs that have sealing flanges or proper weatherproof boots.

Practical Sailor's surveyor points out that by the time discoloration shows on the face of a plug or inlet, the damage behind it is usually greater. Heat travels back along the copper and bakes the insulation inside the plug body, where you can't see it.

So a darkened blade isn't a cleaning job. Treat it as a heat-damaged end and decide in Step 7 what to replace.

Once the cord passes a visual check and is back in use, run your normal loads for an hour or so, then carefully feel each end and the boat inlet with the back of your hand (don't unplug anything under load). Warm can be normal; hot is not. If one end is noticeably hotter than the other, that end, or what it plugs into, has a poor connection. See the heat check in the inlet upgrade guide.

Replace the whole cord if any of these apply:

• The jacket has damage anywhere along its length (Step 2).
• Both ends show heat damage.
• The cord is old and stiff, or the jacket near the damaged end is hard, discolored or cracked.
• The cord or plug has been submerged in salt water for any length of time.
• You don't know the cord's history (a used boat's cord, a dock find).

A replacement end may be reasonable when the cord is in good condition, only one end is damaged, and the damage is limited to the plug itself. BoatUS has noted that some upgraded connector systems are sold so you can refit your existing cord with a new end. Even then, the wire behind a burned end must be cut back until the copper is bright and the insulation is soft and undamaged; if you can't get there and still have enough length, buy a new cord.

Whichever you choose, check what it plugs into. Practical Sailor warns that many owners replace a charred plug or cord only to burn the new one, because the boat's inlet or the dock receptacle was also damaged. A burned boat-end connector means the boat's inlet needs inspection by an electrician; a burned dock-end plug means the marina needs to look at the pedestal outlet.

• Same rating and configuration: a 30-amp end for a 30-amp cord, a 50-amp end for a 50-amp cord, with the same blade layout. Never fit a smaller-rated end, and never fit a household plug.
• Marine and listed: buy a listed marine shore power plug or connector, with a sealing collar or weather boot and a locking ring. Practical Sailor notes the ABYC calls for locking, weatherproof, grounded connectors.
• Fits the cord: the cord grip must clamp the jacket of your cord size snugly.
• A sealed molded cordset is the simplest fix: a new factory cord with molded ends has no field connections to work loose. That's why a whole new cord is often the better buy when the price difference is small.
• Upgraded connector systems: some systems use larger contact areas and different locking designs and come with a matching boat inlet; see the inlet upgrade guide before mixing systems.

Fitting a field-replaceable end to a cord that is completely unplugged is a job some skilled owners do, following the connector maker's instructions exactly. But the consequences of a small mistake are serious: a swapped neutral and ground, a strand of copper touching the wrong terminal, or a screw left loose can energize metal on the boat, cause electric shock in the water or start a fire. Our advice:

• If you have never wired a 120-volt plug and tested it, have an ABYC-certified marine electrician do it.
• 50-amp (125/250-volt) ends, any work on the boat's inlet or the wiring behind it, and any pedestal work are electrician jobs. The marina owns the pedestal; report a damaged outlet rather than fixing it.
• If you do it yourself, follow the maker's strip lengths, terminal assignments and tightening instructions to the letter, and keep the instruction sheet with the cord.

With the cord unplugged at both ends, use the meter's continuity setting to check that each pin on one end connects only to its matching pin on the other end, and that no two conductors are connected to each other. Any doubt, any wrong result, or any wiring color you don't recognize: don't use the cord, and have an electrician test it. After it's back in use, watch the boat's AC panel for a reverse-polarity warning and do the heat check from Step 6.

A cracked or missing ring is one of the easiest fixes. Practical Sailor calls replacement rings an inexpensive part; they slip over the end with some effort, and warming the ring or using a little non-petroleum lubricant helps. Thread the ring fully home every time you plug in so the connector can't wiggle and the seal stays closed. If the threads on the boat's inlet are broken, that's an inlet repair.

• Turn power off at the pedestal before plugging or unplugging, every time.
• Support the cord so its weight doesn't hang on the boat end, and keep it off walkways and out of the water.
• Don't leave the cord plugged into the pedestal when the boat is away. Practical Sailor warns the loose end can fall into the water.
• If a plug does go in the water, switch the pedestal off before retrieving it, then rinse it with fresh water and dry it thoroughly (Practical Sailor's advice), and inspect it closely before reuse. Cruising World adds that a field-wired plug (one with screws you can open) has to be opened, washed, dried and reassembled, which is a job for whoever is qualified to re-end it. A plug that sat in salt water should be replaced.
• Push each end fully in and twist until it locks, at the pedestal as well as the boat, then thread the locking ring home. Secure the cord to the boat so its weight doesn't pull on the connector.
• Fit dust caps, coil the cord loosely without kinks, and store it dry and out of the sun.

Note the cord's rating, length, purchase date and any end replacement (who did it and when) in BoatMend, with photos of both ends. Check both ends every time you unplug; Practical Sailor's surveyor suggests at least monthly for boats that stay plugged in.