A standard 30-amp yellow rubber shore power plug has a black retaining ring and three prongs on its face.
To ensure that the plug is inserted correctly, the ground prong has an appendage that will lock in place when the plug is turned. The other two prongs are the hot and the common (or neutral) leads respectively.
If these prongs are loose, discolored or show heat damage, the plug should be replaced. The damage most likely resulted from a loose or poor-fitting marina shore power connection.
Poor-fitting connections create resistance, which causes heat. The current is forced to jump across the contacts, burning both your plug and the dock receptacle contacts.
To prevent the problem, always check the connection and don’t use loose receptacles. If the receptacle has a threaded fitting for your plug’s retaining ring, use it to secure your plug to the connection.
Make one or two wraps around the dock pedestal base with any extra cord to isolate the electrical connection should the cord be moved. Support the connection and keep it tight.
When you disconnect from shore power, always turn off your vessel’s primary breaker or shore power selector switch because an open circuit will cause arcing, which could damage your equipment, cause a power failure or even start a fire.
If your vessel doesn’t have a single switch, turn off all AC breakers to prevent current flow. As a last resort, turn off or trip the breaker on the dockside power pedestal as well. Remember, arcing affects both the marina receptacle and your shore power cord. –Pat Lemagie
To learn more, take the USPS Marine Electrical Systems course. To find a course near you, contact your squadron educational officer or your local squadron.