Since you have three terminals on a shore connection, wrong polarity can mean that any of these wires are in the wrong position. Not only should you pay attention to the polarity indicator on your boat, we recommend that you keep a plug in polarity indicator aboard and use it every time you hook up to shore power at a different location. Reverse polarity is not only an electrocution hazard, but can also damage electrical equipment. Never trust the power supply at strange docks, but always check the polarity. When hooking up to strange docks, always check your volt meters to make sure you have adequate voltage.
Low voltage is very damaging to electrical equipment.
Turn on the stove or water heater and watch what happens to the meter. Many people think that the circuit breakers on the dock protect their boat. Your main circuit breaker protects your boat's systems. Well, the fact is that it is unprotected. Check out all the top end boats and you will find that they have circuit protection located directly at the shore connectors.