Raritan Reverse Polarity Alarm One Size. 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 appreciate.With a couple of exceptions it should be standard equipment on every boat that is capable of plugging into a common 120-volt AC shore power outlet. Its purpose is to allow the boat owner to verify that the electrical outlet on the dock is wired correctly.When the polarity is incorrect or reversed it is because the hot and neutral wires are switched. Without an indicator light you will not know when this condition exists. Specifications for Raritan Reverse Polarity Alarm: Manufacturer: Raritan Color: Black Package Contents: Raritan Reverse Polarity Alarm Raritan RPA: Reverse Polarity Alarm One Size