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Old 18-06-2021, 06:49   #1
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Shore Power Upgrade - 30 to 50 Amp

I am looking to upgrade my shore power connection from dual 30 amp feeds to a single 50 amp. The dock connection is a single 50 amp, which I am currently using a splitter pigtail to give me the two 30 amp feeds running to the boat's inlets. I purchased the Marinco 50 amp cord, 240 volt 50 amp inlet, and two 50 amp breakers. My panel has two 30 amp main breakers.

I plan to install the inlet and shore power cord, then wire the inlet to the breaker panel, with one of two hots from the 50 amp feed going to each main breaker. Swapping out the 30 amp main breakers for 50 amp mains.

I wanted to make sure there isn't anything else I am missing here?
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Old 18-06-2021, 06:53   #2
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Re: Shore Power Upgrade - 30 to 50 Amp

How large is the boat? How frequently will you connect to other marina's with 50amp service? If everywhere you go is dual 30 amp, then you're back to a splitter ((2x 30) -> 50). What problem is the (50amp -> (2x30amp)) splitter presenting that you're trying to solve?
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Old 18-06-2021, 06:59   #3
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Re: Shore Power Upgrade - 30 to 50 Amp

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How large is the boat? How frequently will you connect to other marina's with 50amp service? If everywhere you go is dual 30 amp, then you're back to a splitter ((2x 30) -> 50). What problem is the (50amp -> (2x30amp)) splitter presenting that you're trying to solve?
It is an older 57' motor cruiser in a liveaboard marina. At times the mains are tripped when using multiple appliances and AC etc, so looking to provide more power. I wouldn't often be going to other marinas but will carry a splitter for that purpose.
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Old 18-06-2021, 12:05   #4
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Re: Shore Power Upgrade - 30 to 50 Amp

You would also want to be sure that the busswork and any metering equipment can handle the additional current. You should be using #6 wire. Be sure there is enough room considering terminals and bend radius, and that any openings you have to go through are large enough.
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Old 18-06-2021, 12:12   #5
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Re: Shore Power Upgrade - 30 to 50 Amp

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You would also want to be sure that the busswork and any metering equipment can handle the additional current. You should be using #6 wire. Be sure there is enough room considering terminals and bend radius, and that any openings you have to go through are large enough.
Yep, using #6 wire, forgot to mention I did already replace the wiring from the shore power switch to the main breakers and from the main breakers to the buss with #6. There is a metal buss across all of the branch circuit breakers, how would I determine if that can handle the 50 amps?
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Old 18-06-2021, 13:13   #6
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Re: Shore Power Upgrade - 30 to 50 Amp

I fail to understand how going from a (50A cord split to 2x30A inlets) to a (50A cord going to 1 50A inlet) is going to increase your power. It's still limited to 50A total.

You say the "mains" are tripped. Is that the 30A breakers on the boat or the 50A breaker on the pedestal? If the former, the problem is either a tired breaker, or too many of your loads are on one breaker.
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Old 18-06-2021, 13:27   #7
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Re: Shore Power Upgrade - 30 to 50 Amp

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I fail to understand how going from a (50A cord split to 2x30A inlets) to a (50A cord going to 1 50A inlet) is going to increase your power. It's still limited to 50A total.

You say the "mains" are tripped. Is that the 30A breakers on the boat or the 50A breaker on the pedestal? If the former, the problem is either a tired breaker, or too many of your loads are on one breaker.
The dock service is 240 volt 50 amp (two 50 amp breakers). Currently we have 120 volt 30 amp connections coming in. By going to the single 240 volt 50 amp cable and inlet, it provides two hots, which are 120 volt 50 amp each. So currently we can only utilize 30 amps on each 50 amp dock pedestal breaker.

At times we overload the 30 amp mains in the boat, not the 50 amp pedestal. There are many 15 amp branch circuits that are fed from the 30 amp main. So giving up 50 amp mains will allow more breathing room for the branch circuits.
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Old 18-06-2021, 13:30   #8
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Re: Shore Power Upgrade - 30 to 50 Amp

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I fail to understand how going from a (50A cord split to 2x30A inlets) to a (50A cord going to 1 50A inlet) is going to increase your power. It's still limited to 50A total.

You say the "mains" are tripped. Is that the 30A breakers on the boat or the 50A breaker on the pedestal? If the former, the problem is either a tired breaker, or too many of your loads are on one breaker.


Two 30 amp cords will provide 60 amps @ 120v

One 50 amp 125/250 cord is capable of supplying 100 amps @ 120v.

I see this a lot of times on older motor yachts (especially Jeffersons). Where they installed twin 30s for some reason.
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Old 18-06-2021, 13:44   #9
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Re: Shore Power Upgrade - 30 to 50 Amp

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Two 30 amp cords will provide 60 amps @ 120v

One 50 amp 125/250 cord is capable of supplying 100 amps @ 120v.

I see this a lot of times on older motor yachts (especially Jeffersons). Where they installed twin 30s for some reason.
Exactly. A marine engineer that was onboard once mentioned for this size boat it should have been designed with a single 50amp connection.
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Old 18-06-2021, 15:22   #10
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Re: Shore Power Upgrade - 30 to 50 Amp

I'm interested in this thread and had a question and an observation. The observation may not apply directly given it sounds like the live aboard marina may be a semi permanent home for the vessel.
Comment: we have used 20+ marinas this year in Florida, the Bahamas and the us East coast and they all seem to be 120v, either fifty or twin thirty. Which leads to my question.
Question: if you rewire a yacht to use single 50a 240v with two legs of 50a is it compatible with a marina that only has 120v?
Is there a down converter? Also we are parked in super yacht basins all the time that I am sure are this 50/240 configuration but we haven't had an issue with twin 30/120 except for being at the max they can handle both in paper and in actual usage. Did we just not ever dock by a 240 pedestal?
Sorry if I am asking a dumb question here but appreciate the original poster opening this discussion.
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Old 18-06-2021, 15:31   #11
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Re: Shore Power Upgrade - 30 to 50 Amp

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I'm interested in this thread and had a question and an observation. The observation may not apply directly given it sounds like the live aboard marina may be a semi permanent home for the vessel.

Comment: we have used 20+ marinas this year in Florida, the Bahamas and the us East coast and they all seem to be 120v, either fifty or twin thirty. Which leads to my question.

Question: if you rewire a yacht to use single 50a 240v with two legs of 50a is it compatible with a marina that only has 120v?

Is there a down converter? Also we are parked in super yacht basins all the time that I am sure are this 50/240 configuration but we haven't had an issue with twin 30/120 except for being at the max they can handle both in paper and in actual usage. Did we just not ever dock by a 240 pedestal?

Sorry if I am asking a dumb question here but appreciate the original poster opening this discussion.


I find it vanishingly rare to see a marina with 50a125v service. Almost every 50a pedestal I run into is 125/250, with a 30a thrown n for good measure.
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Old 18-06-2021, 15:54   #12
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Re: Shore Power Upgrade - 30 to 50 Amp

Ok, so you are stating when we hook up twin 30a 120v we are actually plugged into 240v and just using a single leg per 30? This is where I think I have the mental disconnect bc I don't have 50/240 but that would be optimal given the house load at times.
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Old 18-06-2021, 16:07   #13
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Re: Shore Power Upgrade - 30 to 50 Amp

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Ok, so you are stating when we hook up twin 30a 120v we are actually plugged into 240v and just using a single leg per 30? This is where I think I have the mental disconnect bc I don't have 50/240 but that would be optimal given the house load at times.


If your at a dock with twin 30a outlets, the dock can be wired solely with 120, or can be wired 240v. The quick way to tell is measure voltage between the two hot legs.

Although I’m not sure what this gains you.
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Old 18-06-2021, 16:38   #14
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Re: Shore Power Upgrade - 30 to 50 Amp

you need a single 50a triple pole main breaker. you can't just split the 50a 240v inlet to run to 2 seperate double poles at each panel. by current code it should also be an ELCI / rcd breaker within 10' of the inlet.

so you should put a 50a triple pole ELCI breaker $$$$ near then inlet then split each hot off and the shared netrual to each DP breaker on each existing ac panel. (assuming you have 2 panels now for each 30a inlet) then you could replace the panel ones with standard double pole 50s to feed each panel.
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Old 18-06-2021, 16:40   #15
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Re: Shore Power Upgrade - 30 to 50 Amp

If your dock is wired for 249, there are 4 wires with the green, safety ground, normally carries no current.

When a 3 wire 240 volt (red to black) is split down to 2 120 volt circuits, the neutral (white) carries the difference in current of the red and black).

If the same 3 wires, ignore green) ate fed by a splitter with 2 plugs, 30 or 50 amp, the white,neutral, carries the sum of Ref plus Black.

If you feed from 50 amp circuits on the same leg, the may carry up to 100 Amps without tripping a breaker and will melt.
If you. Split at the dock end use a single .50 or twin 30 amp plugs. Do not use twin 50s.
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