Poles Apart ! Many older boats and some newer ones with AC electrical systems installed by "my buddy the electrician" are not fitted with a polarity indicator light. The following is an e-mail from a SAMS colleague who explains better than me why you should have one installed. Here's an easy way to understand the requirements concerning polarity indicators. If the polarity is reversed, then the neutral (the grounded conductor) is now powered by the hot (ungrounded conductor) line. All appliances and loads on the boat will still work since they don't care from which direction the alternating power comes from. Now let's say there is a fault in one of the loads (like a ground fault/short circuit). Before we look at that, note that if power is properly supplied, the current will increase substantially on the hot line which should trigger the branch supply circuit breaker for the load to trip. That's the main purpose for having the ground system installed (to ensure there is a path for fault currents to go so that they will become high enough to trip the breaker, at the same time keeping the voltage down on the exterior of the faulted component). In a reverse polarity situation, when a ground fault occurs, the current rises substantially on the neutral line, If there is no breaker in the neutral line, the conductor will heat up, cook, and could eventually cause a fire. That's why we have polarity indicators. They tell us there is no over current protection for the neutral conductors supplying power to loads. I surveyed an old Hatteras (1978) which had an electrical system designed by Charlie Game when he was an electrical engineer with Hatteras. Neither the main service supply nor the Air Conditioning supplies had reverse polarity indicators. A little investigation revealed that all the 120v Air Conditioner loads had double pole branch breakers, so reverse polarity indication was not required there. It took a while to find it, but I found the polarization transformer installed in the lazarette (probably not the best place for it due to humidity issues, etc) which provides the main service supply. Having a polarization or isolation transformer negates the need for reverse polarity protection since the polarity is defined by the output of the transformer, and is independent of the input polarity. Hope this helps in the fundamental understanding of the issue involving the need for polarity indicators.

Capt. David Rifkin Quality Marine Services, LLC Society of Accredited Marine Surveyors . Captain Wallace Gouk AMS® Marine Surveyor Port Credit Marine Surveys

Captain Wallace Gouk AMS®, Survey reports accepted world wide by all financial and insurance institutions for sail and power boats servicing Ontario east, west, south and beyond including Niagara-on-the-Lake, St. Catharines, Grimsby, 50 Point, Stoney Creek, Hamilton, Burlington, Oakville, Bronte, Port Credit, Mississauga, Toronto, Oshawa, Pickering, Port Hope, Coburg, Newcastle, Kingston, Brockville, Penetanguishene, Midland, Barrie and Keswick. I have also worked in New York State, Rhode Island, Pennsylvania, Ohio, Michigan, Illinois, Wisconsin, Minnesota, Virginia, Florida and the Bahamas.