Articles: Power

Reverse Polarity Shore Power

As a boater we love to travel. Boats enable us to travel. One of the many reasons we love being a boater. As we move from place to place we can sometimes come across situations we haven’t experienced before. The following is a guide of what to do when you find your boats reverse polarity lights come to light.

Reverse polarity lights indicators light up when our connection to the dock power is connected but the active and neutral conductors don’t marry up with the same conductors on the dock side. This can happen for multiple reasons which I won’t go into today but when it does happen you need to know what it means and what to do.

On most boats 70ft and under, the shore power lead supplies your vessel with 110v AC power. The shore power cable that connects the dock power to your boat has 3 cores inside. An Active, Neutral and an Earth. Now because of the way switchboards are wired. Your AC circuit protection switches the Active conductor. Your Neutrals all get join together and your earths all get join to each other on bus bars. In some switchboard installations, not all, there is a connection between the Neutral and Earth bus bars. This is ok and safe as long as the Active supply doesn’t get connected to it.

When reverse polarity occurs from the dock side supply. You now have switched the Active and Neutral conductors around and the Neutral and Earth bus bars that were before safe, become live. As I mentioned before, in some cases there is a connection between the Earth and Neutral bus bars. If the Active and Neutral conductors are now switch, not only is your Neutral bus Active but so too is your Earth bar. This earth bar connects to all your metal frames and items on your AC systems. Making them Live. This can create a dangerous touch potential and is very serious.

How do you fix this? Well the first thing is to turn off you main switch that supplies your main switchboard and unplug your shore power lead. Most marinas have a service man who can come and change the wiring of the dock power outlet to suit your vessel. If you travel around a lot from dock to dock, one option is to get a reverse polarity switch put in which you can use to just turn in this situation and continue using your boat without rewiring anything. Reverse polarity lights and this switch are easy to install if you have room at your switchboard. If not they can be installed together in a secure location nearby for easy viewing but bust be in line with your shore power input cable.

It’s not a situation that happens a lot but I hope this information helps you and prevents you from getting your wires crossed.


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