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.

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).

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.

Get a certified electrician aboard.

Chances are that's who wired it like that in the first place.

Bob

BobH said:

Chances are that's who wired it like that in the first place.

Bob

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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.

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

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?

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.

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.

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.

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.

psneeld said:

I even think my upgrade to 50A 125/250 service won't be enough for my lowly 40 foot trawler.

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With that set up you'll have 100 amps of 125v. Do you have all 125v appliances like your oven and stove?

henryj2 said:

Would appreciate any thoughts.

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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.

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.

The numbers above the circuit breaker switch on the panel actually reads "50 amps 230 volts"

kulas44 said:

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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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.

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.

N4712 said:

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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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.

kulas44 said:

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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No. If you split the legs of the 50a 125/250 cord like many boats do you have 2 50a 125v incoming lines. So you have 100a of 125v available total, 50a on each leg.

psneeld said:

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...

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While you have 100a of 125v to play with total. You don't have 100a of surge capacity. You only have 50a per leg.

psneeld said:

Correct on the math...not so on the "stupid" part.

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Actually he's not wrong on the stupid part either. While you have 100a of 125v available on a 50a 125/250 cord, 50a on each 125v line, if you try to pull all those amps off the two lines for any length of time you will most likely end up burning out the cord ends or frying the receptacles in doing so.

psneeld said:

A lot of people on here have been questioning my wisdom on my 50A 125/250 upgrade...

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Am I mistaken, my recollection of walking the docks along the Atlantic ICW is that many of the 40ft+ newer trawlers had 50 amp 120/420 service. I am aware of a couple of older Krogen 42s which upgraded from two 30 amp 120v service to a 50 amp 120/240 volt service. In the US southeast with the demand for airconditioning in a marina I think it would be beneficial.

psneeld said:

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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The wasn't directed at you. But you and me both know if you continuously try to get 100A's out of your cord you have 99% chance of meltdown somewhere on shore or on one end of the cord.

Are you going with a true 50A 125/250v or are you splitting the legs up?

All of our AC's running (64k BTU's) run 24 amps 240. With all them running I usually don't like to run the water heater, but small loads like the microwave aren't a big deal. In the Bahamas we run off two 50A cords, one dedicated to HVAC and one for ship loads that's generally enough for us and we're pretty power hungry. Our problem is the genny isn't big enough. Anyways, if ones not enough you can always add a second and dedicate it to HVAC.

My last boat had a separate 30 amp circuit dedicated to the A/C. If it wasn't plugged in, it wouldn't work. I needed 2 power cords or a splitter. I felt 2 cords was better. I would plug in 1 30 amp circuit at a time and check to see if yours is set up that way. But, I agree, get someone in there that knows what he/she is doing, and get an analysis.

I'm not sure why you guys think things melt at rated capacity.....

Things go wrong with high resistance...but I've never had any issue except at the ends with running full amps through shore power cords...and the 30's suffer much greater end burning than the 50's based on just the design which is 1/2 the reason I'm switching...

I've had way more marina CBs pop when at capacity than meltdowns...well...never had a meltdown except with a bad shore power power post.

When I discussed surge...I was just saying that if I was and probably will continure to run at 60-75 amps normal loads...then I still have about 30 amps in reserve for the surges on some appliances and the times I add a heat gun or ceramic heater to an outlet circuit.

Don't worry guys...I've researched this so much that I have found I had to go way beyond the normal sources of info around here including the marina electricians, the large marine electronics outfit here, Paneltronics tech help etc..... I'm pretty sure I have a good handle on it...to the point that I'm scared that the "pros" have so little.

henryj2 said:

The numbers above the circuit breaker switch on the panel actually reads "50 amps 230 volts"

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I'm still leery to say for sure what's going on with your boat.

You should also have a panel with something that says 110V or 115V.

If you don't something is definitely a bit strange...unless the 50A inlet is wired directly to a 230V panel and then one or several of your appliances must be 220.

And again..with a used boat...looking at just the front of panels is a bit dangerous...you really need to understand what is going on behind them.

As a boat owner you have 2 choices in my way of thinking....know everything about your boat yourself and know enough to know what is going on isn't dangerous...or hire experts that you trust with your boat/life to certify that the boat checks out and then they write up a basic operating and systems diagram so you understand at least the basics and the next owner/tech doesn't have to reinvent the wheel.

kulas44 said:

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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50 amps is 50 amps.......unless you have two of them. 50 plus 50 is 100.

I have a 50 amp 125/250 service cord and its two 50 amp split phase leads give me 100 amps on my 40 foot boat. I will take you downtown Miami and give you an hour to draw a crowd and kiss your you know what if I don't have a 100 amps.

I did something very similar for the new owner of my old Mainship Sedan Bridge. I had added 6 DC circuit breaker sub panels to various areas of the boat, installed a Xantrex 2500 invert/ charger with a Link 2000R controller, added an extensive NMEA2000 buss. I ended up using a Word document with embedded PDF's on every piece of equipment and instructions for what each DC panel controlled. I also included an updated AC and DC schematic showing the power distribution. I found it less expensive to run heavy gauge wire to various DC sub panels than to run home runs to a single large DC breaker panel. The boat also had 2 stand alone Xantrex battery chargers, one for the starting batteries that could also charge the house bank if the 2500 failed and a stand alone 40 amp charger in the front of the boat to charge the bow thruster, windlass and wash down pumps battery bank. I could get the boat ready in a few minutes with my eyes closed but not the new owner. I hear he's having fun with the boat and he uses it for cruising much more than I ever did.
Bill