Raritan Reverse Polarity AlarmReverse Polarity Alarm An essential aid for traveling boaters when connecting to unfamiliar dockside power. The quality of marina wiring can vary greatly from place to place and from plug to plug. That is why most boats designed to plug into shore power have a polarity indicator. It is usually a warning light on the AC electrical panel, although it can also be an audible alarm. It is an important safety feature that few boat owners fully understand or