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Shore Power History and the Three Pole Breaker

Shore Power History and the Three Pole "Breaker"

Early Catalinas used a unique, custom made 3 pole shore power breaker at the main panel for boats equipped with shore power as standard equipment.  The 1st and 2nd poles were 30 amp breakers, while the third pole on the breaker was a voltage coil that would trip at 65 Volts.

Early Catalina panel with a single toggle for AC master power visable, in this case, at the top left.

Although there is only one toggle visable, behind the panel all three units are served by one toggle. The single toggle trips all three poles of the breaker assembly.

Voltage Coil

A voltage coil is designed to trip as soon as the rated voltage is measured and is not designed for continuous usage.  Voltage trip ratings are often used for a “Dump Circuit” or “Panic Trip Circuit”, but on these early boats they provided a mechanism to trip the shore power breaker as soon as there was voltage measured between the ground and neutral circuits.  A voltage is present if there is reverse polarity in the shore circuits or if the traditional style shore power plug or inlet have become worn enough to allow for the plug to be inserted incorrectly, i.e. rotated 120 degrees.  See Technical article “SmartPlug Advantages II” to learn more about the dangers of a worn plug or inlet. 

 Voltage coil labeled P3: The third pole causes a trip if anything over 65 volts is present. Note the small white wire that connects pole 2 directly with pole 3. As a result, if there is voltage present in either pole, the voltage coil causes the entire breaker assembly to trip. 

Changes Over Time

In October of 1988 the 3 pole breaker was replaced by a 2 pole breaker that would not trip should the polarity be reversed. The reverse polarity indicator light located right next to the switch provides a good warning that things are not correct and lets the owner know to address wiring issues as soon as the light turns on. 


We have looked at getting the earlier 3 pole breakers for direct replacement on the earlier panels and have been told that they are no longer available. If you have the earlier style 3 pole breaker, it can replaced with the 2 pole breaker. See the attached wiring diagram for reference, but we highly recommend you invite a marine electrician aboard to consult should you decide such a replacement is necessary.  

There were several other changes to AC system that helped make it safer for those on board. In July of 1992 ground fault circuit interrupters were installed to protect each branch of the AC outlets.  In September of 1998 galvanic isolators were added to the ground line to help prevent DC current from entering the AC ground system. This helped to prevent galvanic corrosion. In February of 1999 an additional 2 pole AC breaker was added at the transom, PT #Z2618, as well as fuses within 7” of batteries in charging circuit to make sure all circuits have over current protection.  Both of these additions are required by ABYC, so you might consider adding them to your boat if they have not yet already been retrofitted.