If your shore power inlet looks like this, you know you need to change it. That pin got hot because of a poor connection, which could have been in one of three places:
- Where the wire is connected to the pin, at the back of the inlet fitting.
- Where the plug contact makes contact with the pin
- A poor connection between the wire and the contact in the mating plug
In any case, now you must change out the shore power inlet fitting. But you should also change out the plug which mates with it. Here's why: In order to ensure a good connection, the contacts inside the plug spring apart as the pin from the shore power inlet is inserted. This spring action results from the shape of the contact, the material, and its temper. If the pin has been overheated, its mating contact likely has too, and probably has lost its temper. Therefore, if you only change out the shore power inlet, the connectors in the mating plug, now having lost their springiness, will make a poor connection with the pins in the shore power inlet (see #2, above). The next time the boat draws a big load, it is likely that the plug will heat up, destroying both itself and the newly installed shore power inlet, and possibly even the entire boat.
On shore, "ground" is established by driving a metal rod literally into the ground (your house ground will also be connected to your water supply, which is even more metal in the ground). On the water, what gets used as "ground"? This is not as easy to explain. The obvious answer is: the water. But on a boat, there is something else going on. Much of the submerged external metal on your boat will be protected from galvanic corrosion by attached zincs which, being higher in the electromotive series, will corrode to protect that submerged metal. But if we connect the boat AC ground to the water, then we are at great risk of electrolytically dissolving that external metal! More on this in a moment. Selfishly, look at it this way. If your zinc-protected external metal is attached to your neighbor's external metal, then your zinc will be protecting both your submerged metal and his. If both boats have their green ground wire connected directly to the boat ground, then your zinc will protect his metal. But it is much worse than this... your zinc will also be protecting all the marina's submerged metal as well, starting with your dock. So how to provide the safety protection that a ground delivers to someone onboard, without truly sacrificing your zinc?
Clamp on ammeters do not need to be expensive. So here's another small boat project: get one, and check your boat's electrical system from time to time. Check your neighbor's too! Heating elements in water heaters and coffee pots crack long before they fail completely, motor windings short to their casings thru conductive dust from the brushes, insulation on wires chafes. An annual check is a good thing.