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Old 10-26-2014, 11:24 AM   #1
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electrical circuit question

Our 44' trawler has 3 electrical inlets for shore power: 30 amp, 50 amp, a/c. We have only used 30 amp which sometimes leaves us a little short and the main circuit snaps off. We have been told that if we get the bigger cord and kick up to use the 50 amp inlet we will have more available juice but it will not operate the a/c. We have also been told that the only way we can run a/c from shore power is by using a 50 amp source (available at our marina) and getting a splitter and an additional 30 amp cord and run one cord from the splitter to the 30 amp inlet and the other to the a/c inlet. We are told this will allow us to run the a/c but it will be a separate circuit and will add no more available power for the rest of the vessel. Would appreciate any thoughts.
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Old 10-26-2014, 12:41 PM   #2
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That is the first I have heard of a setup like that...without seeing it and how it is wired into your panels....I would be very hesitant to answer and you should be very cautious of advice without pictures and a better explanation of where the power goes from those outlets (in particular...is it a 50A 125/250V inlet or just a 50A 125V inlet...which is my guess but as I said...different).
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Old 10-26-2014, 01:11 PM   #3
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Whoever wired it like this was a moron. I can understand splitting off the aircon circuit from the main behind an inverter but to run a seperate 30 amp line just for the aircon is a little wierd. It should be fairly easy to convert to 50 amp 125/250 volt. Personally I use a pair of 30 amp cords with a 50 amp plug and splitter (built by me) and have two 50 amp receptacles on the boat. All plug ends and receptacles are 50 amp 125 volt. I just got tired of burnt plugs. No more probs.
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Old 10-26-2014, 01:18 PM   #4
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electrical circuit question

Get a certified electrician aboard.
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Old 10-26-2014, 02:04 PM   #5
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Chances are that's who wired it like that in the first place.

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Old 10-26-2014, 02:34 PM   #6
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Chances are that's who wired it like that in the first place.

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Old 10-26-2014, 02:44 PM   #7
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I thought I had heard/seen it all. This is crazy, unless the 50 amp was put in last. Important issue is whether the 50 amp is 120 or 120/240. If it is 120/240 have an electrician connect the a/c to one of the 50 amp legs. 50 amp 120/240 will power almost any North American boat of less than 55 feet.
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Old 10-26-2014, 02:52 PM   #8
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You are most likely correct. My dock neighbor once told me that after having contacted a ABYC certified electrician and telling him he needed his genny fixed, the guy did a "boat analysis" after which he told the owner that he probably wouldnt need to rewire "the whole boat" and still couldnt fix the gen. He was one of those morons. It was fairly easy to see that no water was coming out of the exhaust and it was overheating. New impellor and he was good. I didnt even rewire his boat. Caveat Emptor
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Old 10-26-2014, 04:59 PM   #9
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I have a 30 amp inlet and a 50 amp inlet. When I bought the boat you had to run a 30 amp cable and a 50 amp cable to run AC. The compressors and air handles were on the 50 amp circuit and the AC water pump was over on the 30 amp panel. I did some load checks and determined that the total boat loads could easily be handled by 50 amps so I tied the panels together and now only use the 50 amp. I think the 30 amp was original equipment and the 50 amp inlet and panel was an add on when someone switched to an electric stove. Pretty hosed up.

Your problem sound a little like mine was. I don't know what your loads are but most boats can run everything they need on a 50amp. Maybe you could send post some pictures of your AC panels. Do you have more than one?
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Old 10-26-2014, 07:16 PM   #10
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Too much tossing around of 50 amps. For 50 amps to be understood it needs to be described by the voltage. 50 amps 125 or 50 amps 250 are completely different. No one is going to be able to understand the problem much less solve it if if it is not described properly.
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Old 10-26-2014, 07:29 PM   #11
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Way too many assumptions being made here.

Is the 50a inlet 120v or 120/240v? Is the HVAC 120v or 240?

What's the HVAC inlet. 30a120v? 50a120v? 50a120/240v?

Can the HVAC be switched to run off any of the other inlets, or just the HVAC inlet?

A wiring diagram is really what's needed.
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Old 10-26-2014, 07:55 PM   #12
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Not really...the same wattage can be brought into the boat 50 amps 250 or 100 amps 125.

Plus for live-aboards...it' just like a house...no one in the US would think a 50 amp service to their house would be enough...in fact, many homes have 150-200 amp service and rightfully so.

I even think my upgrade to 50A 125/250 service won't be enough for my lowly 40 foot trawler.
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Old 10-26-2014, 08:59 PM   #13
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Do You have a AMP meter to monitor your systems draw ?? If you have a temp. gun measure your power cable temps both at the dock outlet and the vessels inlet. Take a reading 6" to the side of the power inlet then look at the plug itself. No more then 10 degree rise in surface temp. Resistance builds heat, which you do not want. When coffee makers, AC motors and aircondion compressors first start the AMP draw is at its greatest. If you smell heat shut it off rite now at the dock.
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Old 10-26-2014, 10:45 PM   #14
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I even think my upgrade to 50A 125/250 service won't be enough for my lowly 40 foot trawler.
With that set up you'll have 100 amps of 125v. Do you have all 125v appliances like your oven and stove?
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Old 10-26-2014, 10:53 PM   #15
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Would appreciate any thoughts.
As has been pointed out no one can answer that question with out a lot more information about how your electrical system set up. Perhaps you should find some one who can at least map it out for you.
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Old 10-26-2014, 11:07 PM   #16
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You will never have 100 amps anywhere no matter what. The service is not cumulative. 50 amp 125 or 50 amp 125/250 is still just 50 amps.
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Old 10-27-2014, 12:53 AM   #17
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The numbers above the circuit breaker switch on the panel actually reads "50 amps 230 volts"
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Old 10-27-2014, 01:15 AM   #18
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You will never have 100 amps anywhere no matter what. The service is not cumulative. 50 amp 125 or 50 amp 125/250 is still just 50 amps.

How so?

50A 125v brings one leg of 120v rated at 50A's.
50A 125/250 brings two legs of 120v rated at 50A's.
They are different. Not the same.

And theoretically you can 100A's of 125v if you split the legs up.


Of course if anyone tries to get 100A's out of their cord, they are plain stupid.
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Old 10-27-2014, 05:30 AM   #19
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100 amps 220 volt is something seen at the megayacht docks. The plug and the cord are massive. Even if a 40+ ft boat had two 50 amp 220 volt shore power inlets the chance of finding a dock which could provide two 50 amp outlets for the same slip would be small. Of course anything could be wired for the home slip, but out cruising one 50 amp outlet would be normal.
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Old 10-27-2014, 06:48 AM   #20
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How so?

50A 125v brings one leg of 120v rated at 50A's.
50A 125/250 brings two legs of 120v rated at 50A's.
They are different. Not the same.

And theoretically you can 100A's of 125v if you split the legs up.


Of course if anyone tries to get 100A's out of their cord, they are plain stupid.
Correct on the math...not so on the "stupid" part...especially when you have 2 or 3 air conditioners that may kick o at the same time.

A lot of people on here have been questioning my wisdom on my 50A 125/250 upgrade...seems to me after 3 times and over 10 years living aboard, lot's of burnt 30 amp connectors and chasing popped CBs all the time because normal living shouldn't have too much load shedding involved...

I'm not sure it's my decision that should be in question...

Sure a boat can live off 12V and use renewable power to supplement a charger....mine just isn't set up that way yet and having 100 amp surge capacity for ACs or a Microwave or any other short term surge is nice in my book with not having to dash to the panel and load shed...

Yes yes Fred, I could have it done automatically...but I'm just gonna live with my 50A 125/250 service, enjoy my 100 amps when I need them and work the boat towards more 12V so eventually I can be free from marina power to a point and happier at anchor.
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