My boat has 2 50A 120V system, tell me about it please...

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Mischief Managed

Mischief Managed

Guru
Joined
Oct 24, 2018
Messages
678
Location
USA
Vessel Name
Mischief Managed II
Vessel Make
1992 Tollycraft 44 CPMY
I was told my new-to-me 1992 Tollycraft 44 is equipped with a "2 50A 120V" shore power system and that it's a standard that was not used long and never caught on. My boat is in storage a long way from home so I can't look at it right now.



Are the two 120V inputs tied together on the boat side? It seems like everything was powered with only one connected when I looked at the boat. Guessing there's a switch to connect the two inputs when only using one inlet and a way to disconnect them when using both inlets. Can anyone confirm that that's the normal way they are wired?



If the two inlets can be disconnected from each other, I think it would be possible to connect the boat to a 240V 50 amp outlet, but my gut says the neutral wire in the cable and the dock wiring could potentially carry 100 amps so that would be a no no. Is there an adapter for such a connection? Any thoughts on this?



My guess is that I could connect to a 50A 240 volt outlet, but I could only make use of one phase (120V) of the 240V and I'd be limited to 50 amps at 120V on the boat. Assuming I have two cords, I could also connect to 2 30A 120 outlets and get 60 amps total power.
 
Mischief Managed said:
I was told my new-to-me 1992 Tollycraft 44 is equipped with a "2 50A 120V" shore power system and that it's a standard that was not used long and never caught on. My boat is in storage a long way from home so I can't look at it right now.



Are the two 120V inputs tied together on the boat side? It seems like everything was powered with only one connected when I looked at the boat. Guessing there's a switch to connect the two inputs when only using one inlet and a way to disconnect them when using both inlets. Can anyone confirm that that's the normal way they are wired?



If the two inlets can be disconnected from each other, I think it would be possible to connect the boat to a 240V 50 amp outlet, but my gut says the neutral wire in the cable and the dock wiring could potentially carry 100 amps so that would be a no no. Is there an adapter for such a connection? Any thoughts on this?



My guess is that I could connect to a 50A 240 volt outlet, but I could only make use of one phase (120V) of the 240V and I'd be limited to 50 amps at 120V on the boat. Assuming I have two cords, I could also connect to 2 30A 120 outlets and get 60 amps total power.
Click to expand...

I had something similar and one of the options we often did was this...
- take a 50/120 "Y" boatside adapter to 50/250 pedestal side and plugged into 2 two 50/120 boat inlets
- the 50/240 side of the adapter went to a 50/240 cord
- the 50/240 cord went to a 50/240 dockside pedestal
That gives both 50 amp lines full power or a total of 100 amps at 120 volts boat side.
 
I suspect that your so called 2 120V 50A shore power system is almost the same as a 240V 50A system the only difference being that the split occurs at the shore power inlet rather than at the electrical panel.


If so that means that each shore power inlet powers one side of a dual buss panel and these sometimes have a switch that combines all loads on one buss so you can power it with one cord.


If all of this is true then just get a 240V 50A to 2 120V 50A splitter and use that to plug into the much more common 240V 50A socket at the dock.


David
 
Mischief Managed said:
I was told my new-to-me 1992 Tollycraft 44 is equipped with a "2 50A 120V" shore power system and that it's a standard that was not used long and never caught on. My boat is in storage a long way from home so I can't look at it right now.



Are the two 120V inputs tied together on the boat side? It seems like everything was powered with only one connected when I looked at the boat. Guessing there's a switch to connect the two inputs when only using one inlet and a way to disconnect them when using both inlets. Can anyone confirm that that's the normal way they are wired?



If the two inlets can be disconnected from each other, I think it would be possible to connect the boat to a 240V 50 amp outlet, but my gut says the neutral wire in the cable and the dock wiring could potentially carry 100 amps so that would be a no no. Is there an adapter for such a connection? Any thoughts on this?



My guess is that I could connect to a 50A 240 volt outlet, but I could only make use of one phase (120V) of the 240V and I'd be limited to 50 amps at 120V on the boat. Assuming I have two cords, I could also connect to 2 30A 120 outlets and get 60 amps total power.
Click to expand...


Are you telling me that you have 2 sockets that are 50a 120v?

Here in the PNW the standard is becoming 30a 120v and 50a 120/240v. 50a 120v plugs are disappearing as well as anything less than 30a. The importance of this is determining what way to go. If in your area the most common plug is 50a 120v. Then you will want to stick with that set up. If 50a 120/240v is the norm then you will want to make some changes.

The system could be tied together using lock out switches or breakers. It is possible to run the whole boat on either, or, or both. We are missing some vital information to advise further.

With a 50a 120/240v plug, you only have 1 neutral as the two power leads are out of phase with each other. Now if you added a splitter and went to 2 50a 120v sockets on the dock and both sockets were in phase then you would have the potential of having 100a on your neutral. All the splitters I am familiar with have circuitry to prevent this.
 
I really appreciate the replies, I think I get it now. Helps that I have a strong background in electrical stuff...



I imagine the needed adapters to connect to 50A 240V or 30A 120V are already on the boat, I just did not think to look for them on the inspection I did. We are planning to drive back out to MI in a couple of weeks to take inventory of everything, get all the manuals, figure out all the electrical system, and take a bunch of measurements, and load some stuff on it for the trip home in the Spring.
 
It may be that there is a 50amp plug on either side of the boat... the input is selected by port and starboard... That was the set up on our similar vintage Defever.
 
After a discussion with someone with w similar boat, I've concluded that the most likely scenario is that one 50A service is for the 3 reverse cycle air conditioners on the boat and the other 50A service is for everything else on the boat.
 
That is how my boat was set up. ACs on one 50A 120 circuit and everything else on the other. I used a 4 wire 250V 50A to 3 wire 120v Y. With the two 120s connected to the boat and the single end connected to the dock cord.
 
Mischief Managed said:
After a discussion with someone with w similar boat, I've concluded that the most likely scenario is that one 50A service is for the 3 reverse cycle air conditioners on the boat and the other 50A service is for everything else on the boat.
Click to expand...


Easy load balancing that way. Its not really balanced so to speak, but you dont have to stress when the breakers are going to throw on hot days. :)


Probably want to measure the line voltage between the 2 hot leads on the pedestal to determine if its 240V or 120V... (opposite phases vs. same phase) it could make a difference in genny configuration.
 
what_barnacles said:
...


Probably want to measure the line voltage between the 2 hot leads on the pedestal to determine if its 240V or 120V... (opposite phases vs. same phase) it could make a difference in genny configuration.
Click to expand...

Then again, you might read 208 Volts. Of course, the 120V appliances won't care.
 
i ave a 240 splitter that splits to 2 50 amp 120 volts its for sale it is like new 150$ new it was 450$ it is a Hubble and not Marine co junk
 
And if you can use a new 50A 120 socket , I have one listed on this board.
 
Thanks for the offers of hardware. I need to inventory what the boat comes with before I start making (possibly redundant) purchases. The boat is in MI, and I am in NH, so it may be awhile before I make the trip to take inventory...
 
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