How do Y adaptors work and will I get full power to my boat

Before I explain about Y adaptors I want the readers to  be aware that this is just a simplified explanation. Under real conditions at the dock and boat amounts of voltage and amps that can be drawn may fluctuate due to other factors such as tolerances of the circuit breakers.

Let us  start with the 30 amp 125  dock receptacle and a boat with two 30 amp 125 volt inlets

Think of the dock as a pool of amps. A 30 amp 125 volt receptacle on the dock has a 30 amp pool  available. The limit to what can be pulled from the dock is the circuit breaker on the dock.  Normally in a 30amp  125 volt  service it has a 30 amp circuit breaker. Now we do have one more limiting factor.  The boat should have a main circuit breaker panel with a main circuit breaker per inlet . These breakers would matching the inlet  example would be a 30 amp 125 volt inlet will have a 30 amp circuit breaker  limiting the amount of amps the boat can  draw from the dock.  What a Y cord allows you do to is to pull  from this 30 amp pool to your boat.   You can have many combinations of amps drawn all adding up to a total of 30 amps or less.  So 10 amps to one inlet and 20 to the other inlet or 15 to one and 15 to the other  … If the boat tries to draw more than 30 amps from either  inlet  the 30 amp circuit breakers in the boats will trip. If the boat tries to draw more than 30 amps  total between the two inlets  the dock 30 amps circuit breaker will  trip.  Example 25 amps from one inlet and 10 amps from the other inlet  25 amps  + 10 amps = 35 amps.  The 30 amp circuit breaker will trip  at 30 amps.

Next lets look at a  50 amp 125 volt dock receptacle and a boat with two 30 amp 125 volt inlets.

In this scenario the dock now has a pool of 50 amps  with the docks  limiting factor being 50 amp circuit breaker on the dock.  The boat  still has only two 30 amp inlets  with the boats limiting factor being  the 30 amp  circuit breakers in the boat. The Y again will allow you to pull a combination of amps totaling now 50 amps  from the pool; However the circuit breakers  on the boat will only allow you  to pull 30 amps per inlet.  So you can have many combinations of amps  all adding up to 50 amps or less  So you could end up pulling 30 amps to one inlet and 20 to the other or 25 and 25 etc.…… If the boat tries to draw more than 30 amps from either  inlet the  30 amp circuit breakers in the boats will trip. If the boat tries to draw more than 50 amps total  between the two inlets  the dock breaker will  trip.  Example 30 amps to one inlet and 30 to the other inlet.  30 amps  +30 amps  = 60 amps  the  50 amp circuit breaker on the dock will trip at 50 amps .

Another scenario is the  50 amp 125/250 dock receptacle on the dock and a boat with  two 30 amp 125 inlets on the boat.

This scenario is a little different. The  50 amp 125/250 contains two hot wires each containing 50 amp 125 volts.  So in essence two pools of 50 amp. The dock will have a dual circuit breaker  each rated 50 amp 125 volts. Again the boat  still has only two 30 amp 125 inlets  with the boats limiting factor being  the 30 amp circuit  breakers in the boat.   In this case you have two pools of 50 amps . The Y adaptor  will allow each 30 amp inlet to pull from one of the pools. The limiting factor being  the  30 amp circuit breakers on the boat. . So in this case you  can draw 30 amps per inlet or less,  but no more than 30 amps as the 30 amp circuit breakers on the boat will trip.  With the 2 breakers on the dock being rated 50 amps the main limiting factor falls on to the boats breakers.  This set up will allow for the most  power to your boat.

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