In the salt water
such burn marks are very common and as Wotname said, an electrical resistance has developed between the plug
terminal and the receptacle terminal - the metal parts
- - If you open up the receptacle housing/cover you will most likely find the same burn evidence and even burnt/fried wire where it connects into the receptacle.
- - If the external and internal terminals and wires are just blackened and not physically "melted/vaporized" away then just clean them.
- - Go to an electrical supplier (cheaper) or marine
store like West Marina (expensive) and get a tube of dielectric silicon grease/compound. Clean and coat the wire strands that go into the receptacle/plug and coat them with the dielectric silicon. Do this also to all the wires (not the insulation). Then likewise, maybe using an artist brush, coat the blade/receiving terminals with the dielectric compound. then reassemble the units.
- - Every so often and especially when "plugging in" to a new dock
box coat your ground power cord's blades with more dielectric silicon. I even use the brush to force some into the dock
box receptacle, but normally just liberally coating your plug
- - The dielectric silicon's only job is to keep the salt water
air from coming in contact with the metal of the wire and plugs/receptacles. It acts like a barrier but does not affect the actual transfer of electricity.
- - As you work on the boat's electrical system
it is a good idea to coat all the accessible terminals and terminal block metal screws/pads with the same dielectric silicon compound. This will go a long way to eliminating the blackening and resistance build-up in your boat's internal wiring
system and help prevent resistance fires from occurring.
- - The downside of using dielectric silicon compound is that everything is "greasy" and it gets on your fingers. But again that is a very minor thing compared to going a long way towards preventing electrical fires. Or in the case of shore power cords, having to purchase
a new one. They are not cheap