Category Archives: Shore Power Inlets

Shore Power Inlets and Fire Safety

With the familiar and ever-present twist-lock style AC shore power inlet connectors almost universally found aboard boats, if there are even the slightest signs of heat in the male or female connectors:

●   a brownish discoloration of the plastic that holds the electrical contact blades in place,
●   obvious melting or deformation of the plastic material that supports the electrical contact blades,
●   inability to get the plugs to twist apart, or
●   color changes in the metal of the blades themselves,

be suspicious that the connections have become a potential source of dangerous overheating.  Overheating problems can affect the connector blades themselves, the plastic blade retainers, or the wire connections on the back side of the blade.

I recommend using an infrared thermometer to “shoot” the temperature of the connector assemblies while they are in use.  On a hot summer day with A/C running, the inlet assemblies should be no more than a degree or two above the ambient air temperature at the inlet location.  If they are hotter than their surroundings, suspect overheating of the blades or connections.  Discoloration and melting plastic means the plug assembly is getting hot.  If you disconnect it and touch the affected male blades, I guarantee you’ll have a burn blister as a result of your experimental curiosity.  How many times the receptacle assembly on your boat can survive overheating before the wires burn off the back side is unknown and unknowable, but if the insulation on those wires gets hot enough, it will erupt spontaneously into flame, and it will burn, damaging anything in the vicinity.


I recommend boat owners physically inspect their interior shore power connections at least annually!  While doing so, make sure the screw attachments at the wire connections are tight.  Immediately replace any connector that shows any signs of discoloration or heating!

There is a new product available for boaters that will greatly reduce this risk of overheating at the shore power inlet connectors on boats.  I strongly recommend replacing the on-board shore power inlet fittings and the mating power cord ends with SMARTPLUGS.   I have done so myself aboard Sanctuary.  These devices replace the “traditional” twist-lock style receptacles at the boat.  Smartplugs are available in both 30A and 50A designs.  They have identical form factors as the twist-lock style, so new mounting holes and screw holes in fiberglass are not required.

Smartplugs have much larger and more robust contact terminals than twist-lock style connectors, and make a much more positive connection.  This prevents the loosening of the contacts and the corrosion of terminals that leads to heating and failure.  The pedestal end of the Smartplug shore power cord is not changed, so compatibility with “normal, ordinary” marina shore power pedestals is completely preserved.  The ability to use a second shore power cord with twist-lock connectors to extend the length of a shore power cord is also preserved.  With Smartplugs, only the boat-end connector is changed.  The earliest version of Smartplug – the ones I have – were fit with a heat sensor.  If the device reaches 200°F, it automatically disconnects the incoming power.  This prevents fire and creates a symptom that alerts the boat owner/operator to the presence of a developing safety problem.

I strongly recommend the Smartplug as an enormous electrical safety advance.  The device won an innovation award from the National Marine Manufacturers Association (NMMA) an the Miami Boat Show in February, 2013.  If interested, the company’s website is here: